GSO 10" f/12 Classical Cassegrain Reflector Telescope - Truss Tube OTA
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- Classical Cassegrain telescope with 250mm aperture and focal ratio of f/12, ideal for visual observation and imaging of the Moon, planets, double stars, planetary nebulae, and other compact celestial objects
- Fully and rigorously tested on site for cosmetics, mechanical operation, and optical performance by a master optician to ensure excellent overall telescope operation and customer satisfaction (an Agena exclusive service)
- Folded optical design packs a focal length of 3000mm into an optical tube only 690mm long, with a weight of 38lbs with all included accessories
- Lightweight Serrurier truss tube for stable mechanics over a wide range of temperature and observing conditions and orientations
- No glass corrector plate means fast temperature equalization and resistance to dew formation; ideal for IR planetary imaging
- Linear bearing 3.25” 10:1 rotatable Crayford focuser with 50mm focus travel and tension and locking knobs to hold heavy loads
- Updated focuser now terminates in an M56x0.75 male thread and is EAF-compatible out of the box. Focuser also includes a built-in removable camera rotator
- Includes 1.25” adapter and two 1” and one 2” M117 extension rings to enable focus with a wide range of cameras and accessories
- Features two Losmandy dovetail mounting rails, two Vixen-style finder bases for guidescope or finderscope, and dust caps for primary and secondary mirrors
1. A Modern Take on a Classic Telescope Design
First conceived in 1672, the classical Cassegrain telescope uses a parabolic primary mirror and a hyperbolic secondary mirror to fold a long focal length into a relatively compact open optical tube. This simple design is ideal for visual observations of the Moon, planets, double stars, planetary nebula, and other objects that are well framed in the tighter fields of view that result from a long focal length.
This 250mm (9.8") f/12 truss-tube Cassegrain from GSO is a modern take on the classical Cassegrain design. With a focal length of 3000mm, it's ideal for serious lunar and planetary imaging and razor-sharp visual observation. This telescope offers views and images that rival and exceed those of large Schmidt-Cassegrain and premium apochromatic refractors.
Because there's no corrector plate on this classical Cassegrain design, the optics are far less susceptible to dewing, and they exhibit much faster temperature equalization because of the open optical tube. The absence of a corrector plate also means this telescope is ideal for imaging planets in the IR to pick up additional detail not seen at visible wavelengths.
These classical Cassegrains come with precisely figured optics, center dot marked secondary mirror, light-weight Serrurier truss tubes for superior image quality, and rugged and precise dual-speed focusers to securely hold your camera and accessories. Unlike compound telescopes like Maksutov or Schmidt-Cassegrains, these classical Casses have fixed mirrors so there's no image shift during focusing, even at very high magnifications. And the 690mm long Serrurier truss tube, which weighs just 38lbs, matches well with nearly any mid-to-high capacity equatorial mount.
2. Full Optical and Mechanical Testing and Quality Control - An Agena Exclusive!
Agena does much more than simply move the telescope boxes from GSO to you. Each GSO Cassegrain (and Ritchey-Chretien and Newtonian) telescope at Agena undergoes a thorough physical, mechanical, and optical evaluation at our shop upon arrival - all at no extra cost to you.
Every GSO telescope is inspected to ensure good cosmetics, collimation, smooth focuser operation, and to make sure all parts are included by the manufacturer. Most importantly, we also check each telescope using a rigorous three-point on-site optical evaluation consisting of the following optical bench tests to ensure that your telescope delivers excellent optical performance:
Foucault Test: This knife-edge test is performed at the center of curvature of the primary mirror to evaluate the quality of the mirror's conic shape.
Ronchi Test: We then perform a Ronchi grating test at the center of curvature at inside focus, at focus, and outside focus. This is a qualitative method to evaluate primary mirror smoothness and figure.
Star test: Finally, we collimate the complete telescope and perform an autocollimation test with an artificial star to examine the overall system's image performance at the focus point.
This testing is performed and certified by a master optician to make sure each GSO instrument sold by Agena has excellent optical performance before it ships. Note that these tests are qualitative and no detailed test reports are included. The telescope will be in perfect collimation when it leaves our warehouse but may require some adjustment after delivery.
3. Diffraction Limited Quartz Primary and Secondary Mirrors for Razor-Sharp Views
Both the parabolic primary and hyperbolic secondary mirrors are made from quartz and ground and polished to a surface accuracy that's diffraction limited or better. Each mirror has enhanced aluminum coatings overcoated with a protective layer of quartz for long life. And each has a reflectivity of better than 96%, similar to Ritchey-Chretien, Schmidt-Cassegrain, and other scopes that cost far more. The secondary mirror is mounted in a four-vane spider, and the central obstruction is about 33%, comparable to most Schmidt-Cassegrain telescopes.
These telescopes are ideal for serious imaging of the Moon and planets, but they can also be used for visual observation. While these telescopes do not exhibit spherical aberration, like Newtonians they will have some coma especially at the lowest magnifications or with astronomy cameras with large chips.
4. EAF-compatible Linear Bearing Focuser with Camera Rotator and Accessories
The solid 10:1 rotatable dual-speed 3.25" Crayford-style linear bearing focuser handles DSLR's, mirrorless cameras, astronomy video cameras, and large sensor CCD and CMOS cameras for astrophotography. It also has a tension knob and a locking knob to allow you to secure heavier loads. The ridged focus knobs give you a good feel and grip, even with gloved hands in cold weather, and the 10:1 fine focus knob lets you snap your image into perfect focus. The drawtube of the focuser is engineered to have minimal wear and very little flexure with most cameras. It offers 50mm of focus travel and includes a focusing scale on the top of the drawtube to make it easy to return to the correct focus position during each observing session.
The linear bearing focuser on this telescope is compatible with the ZWO EAF out of the box without the need for other 3rd party brackets. The bottom of the focuser now incorporates a flat surface with additional screw holes to allow users to easily and directly mount the ZWO EAF using the standard mounting bracket that the EAF comes with. The housing in this version is also made of aluminum for a secure, robust fit. Imagers can now use the EAF to precisely control the focuser's movement for visual or critical imaging applications. Note that the EAF is not included.
This latest incarnation of focusers from GSO also has two more major feature upgrades: 1) The focuser drawtube now terminates in an M56x0.75 male thread. This allows you to directly mate other optional M56x0.75 threaded adapters and accessories (such as a Baader clicklock visual back) for a more secure connection. 2) The focuser now includes a built-in, removable camera rotator with its standard 2" holder. A large thumbscrew lets you lock the rotator at the desired angle to perfectly frame your imaged targets. The camera rotator features M56x0.75 threads on both sides (female on the telescope end and male on the camera side). You can adjust the stiffness of the rotation by tweaking the 3 small screws provided for this with a small flat-head screwdriver.
The focuser on this telescope is decoupled from the primary mirror cell and baffle. It attaches to its own collimating cell on the OTA's backplate so that you can tweak the primary mirror or the focuser alignment independently.
The telescope includes two 1" and one 2" extension rings for situations when you need further backfocus, or when you want to reduce the extension of the focuser's drawtube to minimize its deflection under heavier loads. It also comes with a 1.25"-2" adapter with compression ring so you can use cameras with 1.25" nose pieces.
To enable you to solidly and securely mount the telescope and any other equipment, two 9.8" (250mm) long Losmandy D-plates are included. There are also two Vixen-style bases for mounting a mini guide scope or red-dot or magnifying finders. A primary mirror dust cover and a secondary mirror dust cover are included with the telescope.
With all accessories, the total weight of the tube is 38lbs. For astronomical imaging applications, this RC scope should be paired with an equatorial mount that has sufficient capacity for this weight, along with cameras and other accessories.
5. Carbon-Fiber Serrurier Truss Tube Fast Temperature Equalization Minimal Flexure
The Serrurier truss tube components are made of a strong, light-weight carbon fiber composite material that exhibits extremely low thermal expansion to prevent changes in tube length during temperature changes. The tube design is based on two sets of opposing trusses to resist flexure as the tube orientation changes, even as it passes through the meridian. As a result, the optical elements remain in their optimum position to help achieve the sharpest possible images. The scope also includes a cooling fan for fast temperature equalization.
The scope includes dust caps for the primary and secondary mirrors, Losmandy and Vixen-style dovetail rails for mounting, and M117 extension rings.
6. Specifications
- Optical design: Classical Cassegrain Reflector
- Aperture: 250mm (9.84")
- Illuminated primary mirror diameter: 248.0mm (9.76")
- Focal ratio: f/12
- Focal length: 3000mm
- Primary mirror: Parabolic primary mirror; minimum 96% reflectivity; protective quartz layer
- Secondary mirror: Minimum 96% reflectivity; protective quartz layer; center dot marked for collimation
- Secondary mirror holder: 4-vane all metal spider, 3 collimation screws for alignment of secondary mirror
- Secondary mirror diameter: 78mm
- Secondary mirror holder diameter: 86.5mm
- Secondary obstruction (by diameter / by area): 34.9% / 12.2%
- Available back focus (distance of focal plane from surface of 1.25" eyepiece adapter, with focuser full racked in): 103.3mm. Add 10mm if 1.25" eyepiece adapter is removed.
- Tube outside diameter: 400mm (15.75)" at end ring
- Tube length (without focuser) = 690mm (27.2)". Add 137mm for focuser.
- Tube Material: Carbon Fiber Serrurier Truss
- Focuser: 3.25" dual-speed linear bearing Crayford # DW403
- Tube weight (with all included accessories): 38lbs
- Shipped size / weight = 36"x20"x22" / 48lbs 14oz
- Inspected for collimation and focuser operation at Agena AstroProducts
- Warranty: 2 years
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| Free Shipping Graphic | Free Contiguous US Shipping |
|---|---|
| Telescope Focal Length | 2501 - 3000m |
| Hide Found a better Shipped Price on Frontend? | Yes |
- Classical Cassegrain telescope with 250mm aperture and focal ratio of f/12, ideal for visual observation and imaging of the Moon, planets, double stars, planetary nebulae, and other compact celestial objects
- Fully and rigorously tested on site for cosmetics, mechanical operation, and optical performance by a master optician to ensure excellent overall telescope operation and customer satisfaction (an Agena exclusive service)
- Folded optical design packs a focal length of 3000mm into an optical tube only 690mm long, with a weight of 38lbs with all included accessories
- Lightweight Serrurier truss tube for stable mechanics over a wide range of temperature and observing conditions and orientations
- No glass corrector plate means fast temperature equalization and resistance to dew formation; ideal for IR planetary imaging
- Linear bearing 3.25” 10:1 rotatable Crayford focuser with 50mm focus travel and tension and locking knobs to hold heavy loads
- Updated focuser now terminates in an M56x0.75 male thread and is EAF-compatible out of the box. Focuser also includes a built-in removable camera rotator
- Includes 1.25” adapter and two 1” and one 2” M117 extension rings to enable focus with a wide range of cameras and accessories
- Features two Losmandy dovetail mounting rails, two Vixen-style finder bases for guidescope or finderscope, and dust caps for primary and secondary mirrors
1. A Modern Take on a Classic Telescope Design
First conceived in 1672, the classical Cassegrain telescope uses a parabolic primary mirror and a hyperbolic secondary mirror to fold a long focal length into a relatively compact open optical tube. This simple design is ideal for visual observations of the Moon, planets, double stars, planetary nebula, and other objects that are well framed in the tighter fields of view that result from a long focal length.
This 250mm (9.8") f/12 truss-tube Cassegrain from GSO is a modern take on the classical Cassegrain design. With a focal length of 3000mm, it's ideal for serious lunar and planetary imaging and razor-sharp visual observation. This telescope offers views and images that rival and exceed those of large Schmidt-Cassegrain and premium apochromatic refractors.
Because there's no corrector plate on this classical Cassegrain design, the optics are far less susceptible to dewing, and they exhibit much faster temperature equalization because of the open optical tube. The absence of a corrector plate also means this telescope is ideal for imaging planets in the IR to pick up additional detail not seen at visible wavelengths.
These classical Cassegrains come with precisely figured optics, center dot marked secondary mirror, light-weight Serrurier truss tubes for superior image quality, and rugged and precise dual-speed focusers to securely hold your camera and accessories. Unlike compound telescopes like Maksutov or Schmidt-Cassegrains, these classical Casses have fixed mirrors so there's no image shift during focusing, even at very high magnifications. And the 690mm long Serrurier truss tube, which weighs just 38lbs, matches well with nearly any mid-to-high capacity equatorial mount.
2. Full Optical and Mechanical Testing and Quality Control - An Agena Exclusive!
Agena does much more than simply move the telescope boxes from GSO to you. Each GSO Cassegrain (and Ritchey-Chretien and Newtonian) telescope at Agena undergoes a thorough physical, mechanical, and optical evaluation at our shop upon arrival - all at no extra cost to you.
Every GSO telescope is inspected to ensure good cosmetics, collimation, smooth focuser operation, and to make sure all parts are included by the manufacturer. Most importantly, we also check each telescope using a rigorous three-point on-site optical evaluation consisting of the following optical bench tests to ensure that your telescope delivers excellent optical performance:
Foucault Test: This knife-edge test is performed at the center of curvature of the primary mirror to evaluate the quality of the mirror's conic shape.
Ronchi Test: We then perform a Ronchi grating test at the center of curvature at inside focus, at focus, and outside focus. This is a qualitative method to evaluate primary mirror smoothness and figure.
Star test: Finally, we collimate the complete telescope and perform an autocollimation test with an artificial star to examine the overall system's image performance at the focus point.
This testing is performed and certified by a master optician to make sure each GSO instrument sold by Agena has excellent optical performance before it ships. Note that these tests are qualitative and no detailed test reports are included. The telescope will be in perfect collimation when it leaves our warehouse but may require some adjustment after delivery.
3. Diffraction Limited Quartz Primary and Secondary Mirrors for Razor-Sharp Views
Both the parabolic primary and hyperbolic secondary mirrors are made from quartz and ground and polished to a surface accuracy that's diffraction limited or better. Each mirror has enhanced aluminum coatings overcoated with a protective layer of quartz for long life. And each has a reflectivity of better than 96%, similar to Ritchey-Chretien, Schmidt-Cassegrain, and other scopes that cost far more. The secondary mirror is mounted in a four-vane spider, and the central obstruction is about 33%, comparable to most Schmidt-Cassegrain telescopes.
These telescopes are ideal for serious imaging of the Moon and planets, but they can also be used for visual observation. While these telescopes do not exhibit spherical aberration, like Newtonians they will have some coma especially at the lowest magnifications or with astronomy cameras with large chips.
4. EAF-compatible Linear Bearing Focuser with Camera Rotator and Accessories
The solid 10:1 rotatable dual-speed 3.25" Crayford-style linear bearing focuser handles DSLR's, mirrorless cameras, astronomy video cameras, and large sensor CCD and CMOS cameras for astrophotography. It also has a tension knob and a locking knob to allow you to secure heavier loads. The ridged focus knobs give you a good feel and grip, even with gloved hands in cold weather, and the 10:1 fine focus knob lets you snap your image into perfect focus. The drawtube of the focuser is engineered to have minimal wear and very little flexure with most cameras. It offers 50mm of focus travel and includes a focusing scale on the top of the drawtube to make it easy to return to the correct focus position during each observing session.
The linear bearing focuser on this telescope is compatible with the ZWO EAF out of the box without the need for other 3rd party brackets. The bottom of the focuser now incorporates a flat surface with additional screw holes to allow users to easily and directly mount the ZWO EAF using the standard mounting bracket that the EAF comes with. The housing in this version is also made of aluminum for a secure, robust fit. Imagers can now use the EAF to precisely control the focuser's movement for visual or critical imaging applications. Note that the EAF is not included.
This latest incarnation of focusers from GSO also has two more major feature upgrades: 1) The focuser drawtube now terminates in an M56x0.75 male thread. This allows you to directly mate other optional M56x0.75 threaded adapters and accessories (such as a Baader clicklock visual back) for a more secure connection. 2) The focuser now includes a built-in, removable camera rotator with its standard 2" holder. A large thumbscrew lets you lock the rotator at the desired angle to perfectly frame your imaged targets. The camera rotator features M56x0.75 threads on both sides (female on the telescope end and male on the camera side). You can adjust the stiffness of the rotation by tweaking the 3 small screws provided for this with a small flat-head screwdriver.
The focuser on this telescope is decoupled from the primary mirror cell and baffle. It attaches to its own collimating cell on the OTA's backplate so that you can tweak the primary mirror or the focuser alignment independently.
The telescope includes two 1" and one 2" extension rings for situations when you need further backfocus, or when you want to reduce the extension of the focuser's drawtube to minimize its deflection under heavier loads. It also comes with a 1.25"-2" adapter with compression ring so you can use cameras with 1.25" nose pieces.
To enable you to solidly and securely mount the telescope and any other equipment, two 9.8" (250mm) long Losmandy D-plates are included. There are also two Vixen-style bases for mounting a mini guide scope or red-dot or magnifying finders. A primary mirror dust cover and a secondary mirror dust cover are included with the telescope.
With all accessories, the total weight of the tube is 38lbs. For astronomical imaging applications, this RC scope should be paired with an equatorial mount that has sufficient capacity for this weight, along with cameras and other accessories.
5. Carbon-Fiber Serrurier Truss Tube Fast Temperature Equalization Minimal Flexure
The Serrurier truss tube components are made of a strong, light-weight carbon fiber composite material that exhibits extremely low thermal expansion to prevent changes in tube length during temperature changes. The tube design is based on two sets of opposing trusses to resist flexure as the tube orientation changes, even as it passes through the meridian. As a result, the optical elements remain in their optimum position to help achieve the sharpest possible images. The scope also includes a cooling fan for fast temperature equalization.
The scope includes dust caps for the primary and secondary mirrors, Losmandy and Vixen-style dovetail rails for mounting, and M117 extension rings.
6. Specifications
- Optical design: Classical Cassegrain Reflector
- Aperture: 250mm (9.84")
- Illuminated primary mirror diameter: 248.0mm (9.76")
- Focal ratio: f/12
- Focal length: 3000mm
- Primary mirror: Parabolic primary mirror; minimum 96% reflectivity; protective quartz layer
- Secondary mirror: Minimum 96% reflectivity; protective quartz layer; center dot marked for collimation
- Secondary mirror holder: 4-vane all metal spider, 3 collimation screws for alignment of secondary mirror
- Secondary mirror diameter: 78mm
- Secondary mirror holder diameter: 86.5mm
- Secondary obstruction (by diameter / by area): 34.9% / 12.2%
- Available back focus (distance of focal plane from surface of 1.25" eyepiece adapter, with focuser full racked in): 103.3mm. Add 10mm if 1.25" eyepiece adapter is removed.
- Tube outside diameter: 400mm (15.75)" at end ring
- Tube length (without focuser) = 690mm (27.2)". Add 137mm for focuser.
- Tube Material: Carbon Fiber Serrurier Truss
- Focuser: 3.25" dual-speed linear bearing Crayford # DW403
- Tube weight (with all included accessories): 38lbs
- Shipped size / weight = 36"x20"x22" / 48lbs 14oz
- Inspected for collimation and focuser operation at Agena AstroProducts
- Warranty: 2 years
Â
| Free Shipping Graphic | Free Contiguous US Shipping |
|---|---|
| Telescope Focal Length | 2501 - 3000m |
| Hide Found a better Shipped Price on Frontend? | Yes |
GSO 10" f/12 Classical Cassegrain Reflector Telescope - Truss Tube OTA