Utilizing the same hyperbolic primary and secondary mirror design used in the Hubble Space Telescope, the Keck telescopes, and the ESO Very Large Telescope, the iOptron Photron 250mm f/8 Ritchey-Chrÿtien Catadioptric Telescope (RCT) represents the medium-aperture class in the series and is ideally suited for both stargazing and astrophotography. Despite its larger mirror and long focal length, it delivers views that are free from off-axis comas and spherical and chromatic aberrations, yet maintains a highly portable form factor. The low thermal-expansion quartz primary and secondary mirrors are treated with highly reflective dielectric coatings that, when combined with internal knife-edge baffles, limit distortion as the mirrors heat while limiting stray internal light and maximizing light transmission. All this translates to bright and sharp high-contrast images with accurate color fidelity across the entire distortion-free field of view.
Unlike other catadioptric designs, this RCT has a fixed primary mirror to eliminate the image shift that is common with conventional configurations that move the mirror forward and back to focus the image. With the primary mirror fixed in place, iOptron installed a precise two-speed Crayford-style focuser with a 10:1 reducer that allows for fast coarse and precise fine focusing without the backlash that occurs in the more common rack-and-pinion design—essential for astrophotography or splitting objects that are close together, like binary stars. To ensure complete coverage of today's imaging sensors, the focuser has a 2" drawtube and comes with three extension rings to help users achieve the proper back-focus distance. The larger drawtube also allows the use of large eyepieces, which generally have longer eye reliefs to make visual observations much more comfortable, and comes with a 1.25" reducer to enable the smaller and more common-sized eyepieces and accessories to be easily used.
Intended for those who have a reliable support system, iOptron offers the RCT here as an optical tube assembly (OTA)-only option. A long Losmandy-style dovetail plate is factory installed to make it compatible with a wide variety of heavier-duty alt-azimuth, equatorial, and GoTo mounts that can carry a minimum payload of at least 35 pounds. To make adding accessories, such as a smaller guide scope, or to piggyback imaging or DSLR cameras for wide-field photography, a smaller Vixen-style dovetail plate is also pre-installed on the top of the OT
- Large 250mm (9.8") clear aperture provides performance while keeping the OTA portable; 110mm secondary mirror
- Long 2000mm focal length provides a high magnification potential and moderate focal ratio for astrophotography
- Moderate f/8 focal ratio allows for shorter exposure times for imaging than slower OTAs
- Ritchey-Chrétien catadioptric design delivers views free from off-axis comas and spherical and chromatic aberrations
- Low thermal-expansion quartz primary and secondary mirrors limit distortion as the mirrors heat
- Highly reflective dielectric mirror coatings transmit more than 99% of incoming light to ensure bright and clear images
- 10 internal knife-edge baffles diminish stray light, improving contrast for visual and imaging applications
- Fixed-position primary mirror eliminates image shift common in other catadioptric designs
- Three integrated primary mirror cooling fans reduce acclimation time and help to eliminate distortion due to mirror heating; runs on eight user-supplied AA batteries
- Resolution: 0.46 arcsec
- 10:1 dual-speed linear-bearing Crayford focuser allows for fast coarse and precise fine focus without backlash for tack-sharp focusing; with tension-adjustment knob and drawtube lock knob
- Oversized 3.3" drawtube ensures complete coverage of imaging sensors to eliminate or limit vignetting and terminates in a 2" eyepiece holder that allows the use of larger eyepieces to make viewing easier and more comfortable; with etched scale in inches and millimeters for precise repeatability
- Factory-installed mounting plate for user-supplied finder
- Optical tube assembly only—mount and tripod required for proper use
- Long Losmandy-style dovetail plate is compatible with many alt-az, equatorial, and GoTo mounts
- Weight: 35 pounds
- Secondary upper Vixen-style dovetail plate enables easy mounting of smaller guide scopes or piggybacking imaging or DSLR cameras for wide-field astrophotography
- 2"-to-1.25" reducer allows the use of the smaller, more common-sized accessories and eyepieces in the larger focuser drawtube
- Three focuser rings allow for increased back-focus distance to ensure the focal plane properly lands on imaging sensors or specialized visual equipment
- Rings can be used one at a time or stacked as needed
- Simple screw-together design requires no tools or permanent modification
- Includes two (2) 1" tubes and one (1) 2" tube