This Astro-Tech AT90CFT refractor has:
• 90mm f/6 apochromatic triplet optics using an FCD-100 ED element
• 2.5" dual-speed rotating rack and pinion focuser
• ultra-short 18" length for travel
• 2" and 1.25" compression ring eyepiece holders
• retractable dew shield, dust covers, and 21"x11"x10" padded soft case
• CNC tube rings with a handle and a Vixen dovetail
In the November 2023 issue of Sky & Telescope, Alan Dyer had this to say.
1. Alan had actually reviewed the TMB92SS when we brought it out in 2009, so he is familiar with what we were trying to accomplish.
2. Optically he said, "this is a telescope that should please even the most discerning apo lover."
3. Photographic wise he said, "there is no sign of longitudinal chromatic aberration" and "The AT90CFT is certainly capable of superb images with full-frame cameras."
4. Mechanically, "The telescope's fittings are first-class"
5. In the end he said, "The AT90CFT would be a good candidate for a desert-island telescope." and "I can conclude that it does indeed perform as well as the original TMB92, if not better." and finally "It is certainly a worthy successor to Thomas Back's classic Signature Series TMB-92."
The AT90CFT 90mm f/6 triplet apo is a very compact refractor for the serious observer and traveler. Measuring only about 18" long with the focuser and dewshield retracted for storage and travel, the AT90 optically and mechanically fills the void left by the discontinued AT92, TMB-92, and 90mm f/5 Astro-Physics Stowaway (a legendary scope that sells for up to $6000 on the used market).
The AT90CFT puts exceptionally high optical and mechanical quality in a truly tiny package. It is ideal for the serious observer who will accept nothing less than unsurpassed imaging and visual observing performance in a supremely portable body you can take with you anywhere in the world.
The AT90CFT is a continuation of the legendary TMB92 and AT92. Thomas laid the foundation for this scope when we had him design his ultimate refractor, the TMB-92 Signature Series. The design has set dormant in our "vault" for many years until we thought it was time to dust it off. We sent the design to Roger Ceragioli to give it a once over and make sure that it was performing as it should with advances in glass and coatings over the last decade. He studied it, and made some changes to try and get every ounce of performance possible out of 92mm of glass. The AT92 is a great scope, but we ran into an issue getting a dedicated focal reducer made for it. So we went to the optical designer at the manufacturer that produced the AT92 and started working with the design parameters laid out by Tom and tweaked by Roger. We were able to get fantastic performance, a guaranteed .95 strehl ratio, and have a dedicated .8x reducer field flattener made for the scope as well. We did have to make the scope an f/6 system in its latest incarnation however.
The AT90CFT is an exceptional grab and go scope for observing and imaging - both within the solar system and out to the furthest reaches of infinity. Its images of subtle low-contrast lunar and planetary details are razor-sharp, with realistic and highly saturated color. Those images are free from chromatic aberration of any type, thanks to the ED element in the scope's triplet optics.
The latest antireflection multicoatings and knife-edge internal baffles assure the maximum image contrast possible. Image excellence is limited only by the seeing conditions, not by any aberration or short-coming in the telescope.
This Telescope's Optical and Mechanical Systems . . .
Apochromatic triplet ED refractor optics: 3.5" (90mm) aperture, 540mm focal length, f/6 triplet lens. It uses an FCD-100 ED (Extra-low Dispersion) glass center element in combination with two mating elements for sharp images that are high in contrast and free from spurious color (chromatic aberration).
Multicoated optics: Fully multicoated on all surfaces with the latest antireflection materials for exceptionally high light transmission and excellent contrast. Light transmission is so high that the optics seem to virtually disappear when viewed from head on.
OTA Construction: The optical tube is constructed out of black carbon fiber with matte black metal trim and focuser body.
Internal light baffles: Contrast-enhancing knife-edge light baffles in the optical tube and focuser provide truly dark sky backgrounds and high terrestrial contrast. In addition, the edges of the objective lens are blackened to eliminate contrast-reducing stray internal reflections.
Retractable dew shield: The self-storing retractable dew shield/lens shade slows the formation of dew on the lens to extend your undisturbed observing time. It also improves visual and photographic contrast by shielding the lens from off-axis ambient light (the neighbor's yard light, moonlight, etc.)
Dual-speed 2.5" rotating rack and pinion focuser: The precision-made 2.5" focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with a 10:1 reduction gear microfine focusing ratio. This provides exceptionally precise image control during very high magnification visual observing, and during critical 35mm or CCD imaging. All focus knobs are ribbed, so they are easy to operate, even while wearing gloves or mittens in cold weather. Multiple internal baffles in the focuser drawtube assure high contrast. The focuser comes standard with a vixen style finder shoe. The focuser also comes with a built in Camera Angle Adjuster to really help you frame your images.
Compression ring eyepiece holders: The focuser drawtube ends in a 2" eyepiece holder that uses a non-marring twist lock compression ring to hold a 2" star diagonal and accessories in place. The compression ring won't scratch the barrel of your star diagonal and accessories as an ordinary thumbscrew can. Also supplied is a 1.25" twist lock eyepiece holder that slips into the 2" compression ring holder to let you use a 1.25" star diagonal or image erecting diagonal. Like the 2" eyepiece holder on the eyepiece holder rotation mechanism, the 1.25" adapter also uses a non-marring twist lock compression ring to hold 1.25" star diagonals and accessories in place.
Shipping/storage case: The AT90CFT comes standard in a 21"x11"x10" padded soft case with a carry handle and shoulder strap for transportation and general protection purposes. The soft case has ample padding to protect your scope and has five cutout spaces for various accessories like a diagonal or the optional .8x reducer/field flattener.
Full Dimensions: 19.5" long with dew shield extended. 18" long with dew shield retracted. Dew Shield diameter 4.75". 108mm tube diameter. 11.45 pounds ota weight with rings.
Other supplied accessories: A slip-on metal dust cap is standard. As well as a set of hinged tube rings with a handle and a Vixen dovetail. A vixen style finder shoe is installed on the focuser body.
