George A. Carroll
30-inch (.76M)
Reflector
Optical Properties
Two Telescopes in One
The primary instrument at SRO is a 30-inch (0.76-m) reflecting telescope that can be configured as either a wide-field Newtonian operating at f/6 or a high magnification Cassegrain at f/25. This superb, dual-use scope was designed and built by George A. Carroll with considerable help from the founding members of Stony Ridge Observatory. As with other telescopes so christened after the driving force behind their construction, this one bears Carroll’s name.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman.
As received, the raw glass blank weighed over 400 pounds (181 kg) and was too thick, forcing the recasting of a new blank which was then fashioned. Much of the surface material was removed during coarse grinding, an otherwise laborious exercise if not for a mirror grinding machine constructed by Ensign. As finished, the 300 pound (136 kg) mirror is 5-inches (12.5 cm) thick, a typical proportion for an objective of 30-inch diameter.
Ensign did the final polishing, figuring and testing of the optic. Although the availability of large mirrors is now much more common, even among amateurs, what the SRO group was able to produce in the early 60s, was, and still is, quite remarkable.
When completed in 1963, Stony Ridge’s prized telescope was the eighth largest telescope in California and quite possibly, the largest amateur telescope in the world.
One Tube, Three Mirrors
SRO member Dr. Milan Mijic, Associate Professor of Physics at California State University, Los Angeles (CSULA) is readying the telescope for a night of observing with a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA.
The main mirror, which rests inside the tailpiece shown here, gathers starlight but where that light is focused depends upon an additional reflecting surface (the "secondary") near the top of the tube.
If a flat mirror is installed there, angled at 45 degrees, light is redirected out the side of the tube. This is known as the Newtonian configuration, first perfected by Isaac Newton in 1668.
Alternatively, if the secondary is convex, the light is reflected back toward the primary, escaping the tube through concentric holes in the main mirror and the tailpiece. This optical arrangement is referred to as a "Cassegrain."
The back of the primary mirror is visible through the three cutouts in the tube's rear bulkhead. As the telescope is moved, the heavy glass disk is subject to sagging and thus distortion of the precise curve on its front surface. To prevent this from happening, the mirror must be supported at several strategic points from the back. This is provided by the white pads that can be clearly seen.
One Tube, Three Mirrors
SRO member Dr. Milan Mijic, Associate Professor of Physics at California State University, Los Angeles (CSULA) is readying the telescope for a night of observing with a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA.
The main mirror, which rests inside the tailpiece shown here, gathers starlight but where that light is focused depends upon an additional reflecting surface (the "secondary") near the top of the tube.
If a flat mirror is installed there, angled at 45 degrees, light is redirected out the side of the tube. This is known as the Newtonian configuration, first perfected by Isaac Newton in 1668.
Alternatively, if the secondary is convex, the light is reflected back toward the primary, escaping the tube through concentric holes in the main mirror and the tailpiece. This optical arrangement is referred to as a "Cassegrain."
The back of the primary mirror is visible through the three cutouts in the tube's rear bulkhead. As the telescope is moved, the heavy glass disk is subject to sagging and thus distortion of the precise curve on its front surface. To prevent this from happening, the mirror must be supported at several strategic points from the back. This is provided by the white pads that can be clearly seen.
courtesy Elizabeth Erin Crossman, CSLA
As a Newtonian...
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A secondary mirror is computer controlled (a recent upgrade) to align itself with the desired observing port.
Such provision allows semi-permanent fixturing of cameras, spectrographs, or eyepieces for handy access. In the case of visual observing, this mitigates one of the disadvantages of the Newtonian design in a non-rotating tube: inconvenient orientation of the eyepiece when the scope is pointed to certain locations in the sky.
As a Cassegrain...
A fifth port is located at the back of the telescope tube, at the Cassegrain focus, but using it requires the optical path to be reconfigured.
The Newtonian’s oval, flat-mirror secondary must be replaced with a round, convex-mirror that sends the image from the primary mirror back through a hole at its center.
Swapping out the smaller mirrors necessitates recollimation – realignment – of the main mirror with that newly installed secondary. For this reason, the Newtonian (general-purpose) secondary is most often installed and is only replaced when the Cassegrain focus is required for a specific observing program.
Mechanical
The Mount
The telescope is held within a “fork” mount, in which the tube is suspended by two large tines. The castings for such support are decidedly massive but fork-style mounts offer several substantial advantages over other designs:
- compactness
- allow the telescope to access to all parts of the sky
- continuous tracking of objects through the meridian (local North/South line)
- elimination of large counterweights to balance the tube
A Compact, Robust Mount for a Massive Telescope
Fork mounts are harder to fabricate than other designs, requiring precision on a scale that isn't easy to achieve. Yet telescopes of a size like the Carroll reflector have few other good options.
Notice the hand holds on the periphery of the tube's tail piece. The telescope is so well accommodated in the fork mount that moving it by hand takes surprisingly little effort, though the motor engagment clutches must be loosened first.
A Compact, Robust Mount for a Massive Telescope
Fork mounts are harder to fabricate than other designs, requiring precision on a scale that isn't easy to achieve. Yet telescopes of a size like the Carroll reflector have few other good options.
Notice the hand holds on the periphery of the tube's tail piece. The telescope is so well accommodated in the fork mount that moving it by hand takes surprisingly little effort, though the motor engagment clutches must be loosened first.
Right Ascension Drive
The advantage of “equatorial” mounts over those offering simple left-right, up-down motion (“Altitude and Azimuth,” or Alt-Az) is their ability to track the stars with a single movement of the mount. This motion, around the Right Ascension (RA) axis, is motorized such that one complete turn is made in 23 hours and 56 minutes – the time it takes a star to make one circuit of the sky. (It’s not 24 hours, because motion of the earth in its orbit around the sun reduces the time by around 4 minutes per day.)
No motor spins that slowly, so a means of reduction must be devised. This is most often is achieved by incorporating a worm gear system which is fairly difficult to accurately machine, especially at large scale. As originally outfitted, the Carroll telescope used an ingenious system designed by Carroll himself in which a dual chain, friction drive supplied rotation commands to the polar (RA) axis.
A Novel Approach to Stopping Earth's Rotation
Any research-grade telescope must be able to effectively counteract the effects of Earth's rotation. Typically, this starts by first aligning the polar axis of an equatorial mount to the place in the sky about which the stars appear to "spin." This is a point quite near Polaris, the North Star. Pictured above, the cone of the Carroll telescope's polar axis is so-oriented.
Having done that, the polar axis can then be driven at a rate which follows an object's march across the sky. For most targets, like stars, galaxies, and the planets, this roughly equates to 1 revolution per day. But for the Moon, some asteroids and comets, variable rates of rotation may be necessary. The Carroll telescope has such a range of motor speeds on both axes.
For the 30-inch telescope's RA axis, this was provided by an elaborate and handsomely constructed system based on 28v DC components and a friction drive. In this photo, undoubtedly taken when the telescope was new, they are ready to begin two decades of work of faithfully "freezing" the Earth's eastward rotation as observers locked in on various targets in the skies above Charlton Flats.
A Novel Approach to Stopping Earth's Rotation
Any research-grade telescope must be able to effectively counteract the effects of Earth's rotation. Typically, this starts by first aligning the polar axis of an equatorial mount to the place in the sky about which the stars appear to "spin." This is a point quite near Polaris, the North Star. Pictured above, the cone of the Carroll telescope's polar axis is so-oriented.
Having done that, the polar axis can then be driven at a rate which follows an object's march across the sky. For most targets, like stars, galaxies, and the planets, this roughly equates to 1 revolution per day. But for the Moon, some asteroids and comets, variable rates of rotation may be necessary. The Carroll telescope has such a range of motor speeds on both axes.
For the 30-inch telescope's RA axis, this was provided by an elaborate and handsomely constructed system based on 28v DC components and a friction drive. In this photo, undoubtedly taken when the telescope was new, they are ready to begin two decades of work of faithfully "freezing" the Earth's eastward rotation as observers locked in on various targets in the skies above Charlton Flats.
The original drive system was based on 28v DC, a standard in the the aviation industry and one with which George Carroll was quite familiar. In the 1980s, Associate Member Tim Cann converted the power source to 110v AC which required replacing most of the electronic components of the drive mechanism pictured above.
Upgrades
Beginning in the 1980s, significant changes to the mount's subsystems were made. One of the first was to adopt 110v as the source standard, this to replace the 28v system (that had been transformed and rectified from 110) that powered components of the original drive system.
The "new" spur gear set and small driving motor as well as the dual chains from that earlier era are pictured here as they appeared in 1982. Advanced technologies offer the promise of an improved experience but don't always translate for a variety of reasons. This modification did not prove successful and was later removed.
The brass plate with silver handles has a nautical look but isn't used to steer - it is the RA friction clutch. When released, it allows the telescope's polar axis to be rotated manually for gross positioning or maintenance.
Upgrades
Beginning in the 1980s, significant changes to the mount's subsystems were made. One of the first was to adopt 110v as the source standard, this to replace the 28v system (that had been transformed and rectified from 110) that powered components of the original drive system.
The "new" spur gear set and small driving motor as well as the dual chains from that earlier era are pictured here as they appeared in 1982. Advanced technologies offer the promise of an improved experience but don't always translate for a variety of reasons. This modification did not prove successful and was later removed.
The brass plate with silver handles has a nautical look but isn't used to steer - it is the RA friction clutch. When released, it allows the telescope's polar axis to be rotated manually for gross positioning or maintenance.
Auxiliary Telescopes
Six-inch "Guide" Telescope
Mounted on the tube of the 30-inch is long focus (f/15), six-inch (15.2 cm) refractor designed and built by George Carroll. It serves as a companion optic mainly for fine guiding of the telescope during long exposure astrophotography.
Traditionally this was done by visually sighting a star and keeping it centered on the crosshairs of a high-magnification eyepiece via a hand-paddle that controlled the RA and Dec motors.
Modern means employ a sensitive CMOS or CCD digital camera to monitor the star and provide automatic correction commands to the mount.
Even if a perfectly accurate driving mechanism could exactly “cancel” the earth’s rotation, guiding corrections would still be required due to the effects of atmospheric refraction on the star. This is most pronounced near the horizon and generally diminishes as the star gains altitude.
To assist in finding a suitably bright star upon which to guide, the telescope is fitted with a movable stage that holds the guiding eyepiece. It allows the observer to center the guiding camera or eyepiece at a suitable location in the focal plane while still keeping the guide scope aligned with the main tube and pointed straight ahead.
This feature is of lesser importance if a digital camera is used to guide, as the guiding software can choose any star it “sees,” even if that star isn’t centered on the sensor.
Five-inch "Finder"
Another refractor (and Carroll creation) is attached for wide field target acquisition.
The five-inch (12.7 cm) glass operating at f/5 is best used for centering the telescope on bright targets when it’s not in the usual “go-to” mode under computer control. Like the six-inch, it can be used for visual enjoyment, especially on objects of extended size.
Six-inch "Guide" Telescope
Mounted on the tube of the 30-inch is long focus (f/15), six-inch (15.2 cm) refractor designed and built by George Carroll. It serves as a companion optic mainly for finely guiding the telescope during long exposure photography. Traditionally this was done by visually sighting a star and keeping it centered on the crosshairs of a high-magnification eyepiece via a hand-paddle that controlled the RA and Dec (Declination axis) motors.
Modern means employ a sensitive CMOS or CCD camera to monitor the star and provide automatic correction commands to the mount.
Even if a perfect driving mechanism could exactly counteract the earth’s rotation, guiding corrections would still be required. This is due to the effects of atmospheric refraction which slightly displaces objects from where the driving mechanism expects them to be. This is most pronounced near the horizon and generally diminishes as an object gains altitude.
To assist in finding a suitably bright star upon which to guide, the telescope is fitted with a movable stage that holds the guiding eyepiece or camera. This allows the astrophotographer to frame the object in the main scope first and then align the guiding eyepiece to the desired star. (Without this provision, the astronomer would have to center the guide star in the six-inch first and accept the resultant framing in the main scope.)
Guide cameras and their controlling software now provide the same functionality as the moveable stage. They can electronically choose any suitable star seen by camera and guide on it, even if it isn’t centered in the field of view.
Five-inch "Finder"
Another refractor (and Carroll creation) is installed for wide field target acquisition. The five-inch (12.7 cm) glass operating at f/5 is best used for manually locating bright targets when the telescope isn’t being used in the usual “go-to” mode under computer control. Like the six-inch, it can be used for visual enjoyment, especially on objects of extended size.
Optical Properties
section_heading_P
Two Telescopes in One
Finding an Asteroid...before it finds us
Two Telescopes in One
Two Telescopes in One
The primary instrument at SRO is a 30-inch (0.76-m) reflecting telescope that can be configured as either a wide-field Newtonian operating at f/6 or as a high magnification Cassegrain at f/25. This superb, dual-use scope was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory. As with other telescopes so christened after the driving force behind their construction, this one bears Carroll’s name.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman.
As received, the raw glass blank weighed over 400 pounds (181 kg) and required much of the material to be removed during coarse grinding, an otherwise laborious exercise if not for a mirror grinding machine constructed by Ensign. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror of that era.
Ensign did the final polishing, figuring and testing of the optic. Although the availability of large mirrors is now much more common, even among amateurs, what the SRO group was able to produce in the early 60s, was, and still is, remarkable.
Two Telescopes in One
The primary instrument at SRO is a 30-inch (0.76-m) reflecting telescope that can be configured as either a wide-field Newtonian operating at f/6 or as a high magnification Cassegrain at f/25. This superb, dual-use scope was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory. As with other telescopes so christened after the driving force behind their construction, this one bears Carroll’s name.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman.
As received, the raw glass blank weighed over 400 pounds (181 kg) and required much of the material to be removed during coarse grinding, an otherwise laborious exercise if not for a mirror grinding machine constructed by Ensign. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror of that era.
Ensign did the final polishing, figuring and testing of the optic. Although the availability of large mirrors is now much more common, even among amateurs, what the SRO group was able to produce in the early 60s, was, and still is, remarkable.
Photography is at the heart of
"Don't Blink and You'll Miss It...?!"
This machine, called a "Blink Comparator," was used to find new solar system objects, including asteroids. https://creativecommons.org/licenses/by/2.0/
Pretzelpaws with a Casio Exilim EX-Z750 camera. Cropped 8/16/05 using the GIMP
CC BY-SA 3.0, via Wikimedia Commons
"Don't Blink and You'll Miss It...?!"
This machine, called a "Blink Comparator," was used to find new solar system objects, including asteroids. https://creativecommons.org/licenses/by/2.0/
Media Credit:<br>Pretzelpaws with a Casio Exilim EX-Z750 camera. Cropped 8/16/05 using the GIMP<br>CC BY-SA 3.0, via Wikimedia Commons
The George A. Carroll 30-inch Telescope at Stony Ridge
The primary instrument at SRO is a 30-inch (0.76-m) reflecting telescope that can be configured as either a wide-field Newtonian operating at f/6 or as a high magnification Cassegrain at f/25. This superb, dual-use scope was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory. As with other telescopes so christened after the driving force behind their construction, this one bears Carroll’s name.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman.
As received, the raw glass blank weighed over 400 pounds (181 kg) and required much of the material to be removed during coarse grinding, an otherwise laborious exercise if not for a mirror grinding machine constructed by Ensign. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror of that era.
Ensign did the final polishing, figuring and testing of the optic. Although the availability of large mirrors is now much more common, even among amateurs, what the SRO group was able to produce in the early 60s, was, and still is, remarkable.
In Memoriam...
The individuals who founded SRO comprised a range of talent and of age. Youthful in spirit and determination, all, for nothing less could have crossed a finish line that sometimes seemed as distant as the stars themselves.
None of the founding members are still alive. The last of them, John Sousa, was a young man when they began their journey of dreams and toil, and the last to set foot inside the dome. Perhaps when nearing the doorway on that final visit he paused to see his name clustered with the others as shown here, and thought back to a day of satisfaction and triumph when they posed for the photo on this page.
They gathered just steps away from where this plaque is permanently installed, each man having taken a leap of faith in the others and landing, shoulder to shoulder, at the mountaintop
temple of their making.
The George A. Carroll 30-inch Telescope at Stony Ridge
Optical Properties: Two Telescopes in One
The primary instrument at SRO is a 30-inch (0.76-m) reflecting telescope that can be configured as either a wide-field Newtonian operating at f/6 or as a high magnification Cassegrain at f/25. This superb, dual-use scope was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory. As with other telescopes so christened after the driving force behind their construction, this one bears Carroll’s name.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman.
As received, the raw glass blank weighed over 400 pounds (181 kg) and required much of the material to be removed during coarse grinding, an otherwise laborious exercise if not for a mirror grinding machine constructed by Ensign. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror of that era.
Ensign did the final polishing, figuring and testing of the optic. Although the availability of large mirrors is now much more common, even among amateurs, what the SRO group was able to produce in the early 60s, was, and still is, remarkable.
One Tube, Three Mirrors
Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) is readying the telescope for a night of observing with a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA.
The main mirror, which rests inside the tailpiece shown here, gathers starlight but where that light is focused depends upon a second reflecting surface near the top of the tube.
If a flat mirror is used, angled at 45 degrees to the light path, light is reflected out the side of the tube. This is known as the Newtonian configuration, first perfected by Isaac Newton in 1668.
Alternatively, if a convex mirror is used instead, the light is reflected back toward the primary, escaping the tube through concentric holes in the mirror and the tailpiece. This optical arrangement is referred to as a "Cassegrain."
The back of the primary mirror is seen through the three cutouts in the tube's tailpiece. To prevent sagging and preserve the precise curve on the glass's surface as the telescope moves, the mirror must be supported at several strategic points from the back. This is provided by the white pads that can be clearly seen.
Media Credit: Elizabeth Erin Crossman, CSULA
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port. Such provision allows semi-permanent fixturing of cameras, spectrographs, or eyepieces for handy access. In the case of visual observing, this mitigates one of the disadvantages of the Newtonian design in a non-rotating tube: inconvenient placement of the eyepiece in when the scope is pointed at certain locations in the sky.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
Swapping out the secondary mirrors necessitates recollimation – realignment – of the main mirror with that newly installed secondary. For this reason, the Newtonian (flat) secondary is most often installed and is only replaced when the specialized need of the Cassegrain focus is needed to support a specialized observing program.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
The primary instrument at SRO is a fork-mounted, 30-inch (0.76-m) reflecting telescope having two configurations (ratios): Newtonian (f/6) or Cassegrain (f/25). This superb instrument was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The Mount
The telescope is supported by a “fork” mount, in which the tube is suspended by two large tines. The castings for such support are decidedly massive but fork-style mounts offer several substantial advantages over other equatorial mounts: compactness, access to all parts of the sky, the ability to continuously track an object as it passes from east to west across the local meridian, the elimination of large counterweights to balance the tube.
A Compact, Robust Mount for a Massive Telescope
Fork mounts are harder to fabricate than other designs, requiring precision on a scale that isn't easy to achieve. Yet telescopes of a size like the Carroll reflector have few other good choices.
Notice the hand holds on the tail piece of the tube. The telescope is so well accommodated in the fork mount that moving it by hand takes suprisingly little effort.
As received, the raw glass blank weighed over 400 pounds (181 kg) and much thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror. (A 6:1 ratio was typical for that era.)
Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of material that had to be worn away. But thanks to Roy’s motorized grinding machine, the removal was only endlessly noisy and nerve racking, not laborious.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The primary instrument at SRO is a fork-mounted, 30-inch (0.76-m) reflecting telescope having two configurations (ratios): Newtonian (f/6) or Cassegrain (f/25). This superb instrument was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The Right Ascension Drive
The advantage of “equatorial” mounts over simple left-right, up-down (“Altitude and Azimuth,” or Alt-Az) is the ability to track the stars with a single movement of the mount. This motion, around the Right Ascension axis, is motorized such that one complete turn is made in 23 hours and 56 minutes – the time it takes a star to make one circuit of the sky. (It’s not 24 hours, because motion of the earth in its orbit around the sun reduces the time by around 4 minutes per day.)
No motor spins that slowly, so a means of reduction must be devised. Often times this is achieved by employing a worm gear driving system which is notoriously difficult to accurately machine. As originally outfitted, the Carroll telescope used an ingenious alternative designed by Carroll himself in which a dual chain, friction drive provided the rotation of the polar (RA) axis.
A Novel Approach to Stopping Earth's Rotation
Any research-grade telescope must be able to counteract the effects of Earth's rotation. Typically, this is done by first aligning the polar axis of an equatorial mount to the place in the sky about which the stars appear to "spin." This is a point quite near Polaris, the North Star. Pictured above, the cone of the Carroll telescope's polar axis is so-oriented.
Having done that, the polar axis can then be driven at a rate which matches an object's march across the sky. For most objects like stars, galaxies, and the planets, this roughly equates to 1 revolution per day. But for the moon, some asteroids and comets, higher rates of rotation are necessary to keep pace with their motion. The Carroll telescope has such a range of tracking speeds.
As received, the raw glass blank weighed over 400 pounds (181 kg) and much thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror. (A 6:1 ratio was typical for that era.)
Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of material that had to be worn away. But thanks to Roy’s motorized grinding machine, the removal was only endlessly noisy and nerve racking, not laborious.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The primary instrument at SRO is a fork-mounted, 30-inch (0.76-m) reflecting telescope having two configurations (ratios): Newtonian (f/6) or Cassegrain (f/25). This superb instrument was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
Six-inch Guide Scope and Five-inch “Finder”
Mounted on the tube of the 30-inch are two refracting telescopes, each designed and built by George Carroll. The larger features a six-inch (15.2 cm) lens operating at f/15 while the other is a “faster” 5-inch glass (12.5cm) having an f/5 focal ratio. This smaller telescope, with its wide field of view, helps visually locate targets and is handy for quickly acquiring brighter targets for the main telescope.
The long focus, narrow-field optic of the larger telescope provides the means to guide the main telescope during long-exposure photographs.
Traditionally, this was done by visually sighting a star and keeping it centered on the crosshairs of a high-magnification eyepiece. Modern means employ a sensitive CMOS or CCD camera to monitor the star and provide automatic correction commands to the mount’s RA and Dec motors.
Even if a perfectly accurate driving mechanism could counteract the earth’s rotation, guiding corrections would still be required due to the effects of atmospheric refraction on the star. This is most pronounced near the horizon and generally diminishes as the star gains altitude.
To assist in finding a suitably bright star upon which to guide, the telescope is fitted with a movable stage. This allows the observer to move the camera or eyepiece over the focal plane while still keeping the guide scope pointed straight ahead.
Subordinate Telescopes, Each One Important
The long, bluish tube of the six-inch guide telescope is well seen in this photograph showing the telescope as it appeared c1964. It's primary use was to provide corrections to the main driving motors during long-duration photography, a tedious, demanding necessity owing to several mechanical and atmospheric factors.
The short, squat tube atop the 30-inch tailpiece is a wide field "finder" telescope which can be used to help aim the large scope which has a much narrower field of view. The lens of the finder is 5 inches in diameter and could suffice as a fine amateur telescope in its own right, as could the larger guide telescope.
As received, the raw glass blank weighed over 400 pounds (181 kg) and much thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror. (A 6:1 ratio was typical for that era.)
Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of material that had to be worn away. But thanks to Roy’s motorized grinding machine, the removal was only endlessly noisy and nerve racking, not laborious.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The primary instrument at SRO is a fork-mounted, 30-inch (0.76-m) reflecting telescope having two configurations (ratios): Newtonian (f/6) or Cassegrain (f/25). This superb instrument was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
Upgrades
Mounted on the tube of the 30-inch is a six-inch refracting telescope operating at f/15. This high-magnification, narrow field of view optic provides the means to guide the main telescope during long-exposure photographs.
Traditionally, this was done by visually sighting a star and keeping it centered on the crosshairs of a high-magnification eyepiece. Modern means employ a sensitive CMOS or CCD to follow the star and provide automatic commands to the mount’s RA and Dec motors.
Even if a perfectly accurate driving mechanism could counteract the earth’s rotation, guiding corrections would still be required due to the effects of atmospheric refraction on the star. This is most pronounced near the horizon and generally diminishes as the star gains altitude.
To assist in finding a suitably bright star upon which to guide, the telescope is fitted with a movable stage. This allows the observer to move the camera or eyepiece over the focal plane while still keeping the guide scope pointed straight ahead.
Subordinate Telescopes, Each One Important
The long, bluish tube of the six-inch guide telescope is well seen in this photograph showing the telescope as it appeared c1964. It's primary use was to provide corrections to the main driving motors during long-duration photography, a tedious, demanding necessity owing to several mechanical and atmospheric factors.
The short, squat tube atop the 30-inch tailpiece is a wide field "finder" telescope which can be used to help aim the large scope which has a much narrower field of view. The lens of the finder is 5 inches in diameter and could suffice as a fine amateur telescope in its own right, as could the larger guide telescope.
As received, the raw glass blank weighed over 400 pounds (181 kg) and much thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick, a typical proportion for a 30 inch diameter mirror. (A 6:1 ratio was typical for that era.)
Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of material that had to be worn away. But thanks to Roy’s motorized grinding machine, the removal was only endlessly noisy and nerve racking, not laborious.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
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Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.
The primary instrument at SRO is a fork-mounted, 30-inch (0.76-m) reflecting telescope having two configurations (ratios): Newtonian (f/6) or Cassegrain (f/25). This superb instrument was designed and built by George A. Carroll with considerable help from the members of Stony Ridge Observatory.
When completed in 1963, Stony Ridge’s 30-inch telescope was the eighth-largest telescope in California, and most likely the largest amateur telescope in the world.
Between 1957 and 1963, SRO members produced a film that documented the progress of the construction of the telescope and observatory – from the delivery of the mirror blank for grinding and polishing in Altadena, CA, to the opening of the dome and celebration of first-light in 1963. You may view or download a digital version here.
One unique design feature of the telescope was the use of a dual-chain, friction drive system that did not rely on expensive, high-precision gears to accurately move the telescope to follow the stars in the sky. This system has worked with accuracy and precision for 47 years.
The primary mirror, made from a disk of Hayward C-3 glass, was ground and polished by members of SRO under the direction of Roy Ensign and Easy Sloman. Roy did the final polishing,figuring and testing of the mirror.
The raw glass blank started out weighing over 400 pounds(181 kg) and was several inches thicker than it is now. The finished mirror tips the scale at about 300 pounds (136 kg) and is 5-inches (12.5 cm) thick (a thickness ratio of 6:1 was typical for astronomical mirrors of that time). Any amateur telescope maker who has “pushed glass” will certainly wince at that amount of glass worn away. But thanks to Roy’s motorized grinding machine, the grinding was only endlessly noisy and nerve racking, not muscle stressing.
Four eyepiece/instrument ports, located near the top end of the telescope tube at the Newtonian focus, are positioned at each of the 4 cardinal points. A rotating secondary mirror is computer controlled (a recent upgrade) to position itself to reflect the image path to the desired observing port.
A fifth port is located at the back of the telescope tube, at the Cassegrain focus.
The Newtonian secondary flat-mirror is switched out with a round convex-mirror that reflects the image from the primary mirror, returning it back to the primary and through a hole in the center of that mirror, to the Cassegrain focus, located outside the back of the tube.
The main telescope tube has two refractor telescopes mounted to it, a 5-inch (12.5 cm) f/5, and a 6-inch (15.2 cm) f/15 telescope. These instruments, including the optical glass lens elements, were both designed and built by George Carroll.
The 6-inch telescope has an movable x/y stage in front of the eyepiece which allows the observer to reposition the image in relation to the image being observed through the 30-inch. This feature is particularly useful when selecting guide stars when imaging through the main telescope.
Upgrades to the telescope
As new technologies have been developed through the years, Stony Ridge Observatory has endeavored to keep pace.
As a longtime SRO member, Timothy Cann has been Stony Ridge’s guiding light through these years of paradigm shifts. A professional IT consultant by trade, with the passion and skills to produce high-precision machine work, Tim has continued to keep the parts of the mechanism called Stony Ridge Observatory repaired, greased, maintained and moving forward for many years.
During the 1980’s, one of Tim’s first upgrades was to convert the telescope’s electrical system, a 28-volt DC system borrowed from George Carroll‘s professional occupation as an aircraft designer, to a “modern-day” 110-volt AC system. This upgrade required a complete rebuild of the original drive motors.
The photo above (courtesy Elizabeth Erin Crossman, CSULA) shows Dr. Milan Mijic, Associate-member at SRO and Associate Professor of Physics at California State University, Los Angeles (CSULA) readying the telescope for a group of students and faculty visiting from the Science Visualization Laboratory at CalState LA for a night of observing. Click on the image for a high-res, 800KB version.
***************************
Later, the remote servos, devices that connected to clock faces that were used to tell the observer where the telescope was pointed on the sky, were replaced by digital encoders and digital position readout displays.
After that came the addition of a digital computer interface that allowed off-the-shelf telescope control software to read the telescope’s position.
The stage had been set for the latest upgrade. The computer could understand where the telescope was pointing, but the telescope couldn’t understand anything the computer was saying to it, a situation called an open-loop. Closing this loop would require the retirement of the original 2-chain drive system.
A new harmonic-drive system was recently designed and installed by Tim Cann, replacing the original chain drive, and closing the loop. The telescope is now “smart” enough to understand what the computer tells it to do, how fast to move and where to go. The new drive system is operational and currently undergoing engineering tests.
The Station Fire, which nearly destroyed the observatory in the summer of 2009, has delayed the continued use of the telescope, the engineering tests, and the astronomical and outreach projects that were in progress.
scb 5/7/2010
The photo below shows Dave Thomas adjusting the RA clutch. The original drive motor can be seen in the taller of 2 plexiglass cabinets. Relays and gearing are housed in the shorter cabinet.