Astro-Tech AT90CFT Limited Edition f/6 Triplet APO Refractor Carbon Fiber OTA

Description

“I originally purchased this scope with it intended to be my main smaller refractor imaging telescope, however after a night out visually observing with it, I am happy to say I might have some wrestling matches with my priorities in the future. It provided quite a pleasurable viewing experience… wonderfully crisp views of the craters and features along the terminator… M81 and M82 just really popped nicely in my 14mm eyepiece.”
Cloudy Nights AT90CFT First Light discussion. This owner bought the scope primarily for imaging but was surprised by the visual performance on first light.

“First light with my new Astro-Tech AT90CFT, using the AT 0.8x reducer/flattener… stars… round, all the way to the edge… it looks like everything is really well matched.”
Cloudy Nights AT90CFT first light imaging discussion. This owner imaged M31 with the 0.8x reducer and a ZWO 533MC Pro on their very first night with the scope.

Observing Tip

The AT90CFT cools down quickly the carbon fiber tube and compact triplet objective reach thermal equilibrium faster than most refractors this size. But if you’re chasing planetary detail at 150x+, give it 2030 minutes outside before pushing the magnification. Watch the diffraction pattern on a bright star: when the rings are concentric and steady, you’re there. For imaging, use the built-in Camera Angle Adjuster to frame your target before you start exposing it saves you from having to unthread and reclamp the camera to rotate the field.

FAQ

What glass does the AT90CFT use?
The triplet objective uses an FCD-100 ED center element with two mating elements. FCD-100 is an extra-low dispersion glass that provides excellent color correction across the visual and photographic spectrum on par with scopes using FPL-53. Every AT90CFT ships with a guaranteed Strehl ratio of 0.95 or better.

How does this compare to the AT90EDX?
The AT90EDX uses the same optical design and FCD-100 triplet as the AT90CFT, but in a conventional painted aluminum tube. The carbon fiber tube on the AT90CFT is lighter, thermally more stable, and honestly better looking. If weight and travel portability matter to you, the CFT is the one to get. If you want the same optics at a lower price point, the EDX delivers identical views.

Is this a good imaging scope?
Yes. With the dedicated AT90CFTRF 0.8x reducer/field flattener (sold separately), the system becomes a 432mm f/4.8 imaging platform with a flat, corrected field. That’s fast enough for one-shot-color deep-sky imaging with modern CMOS cameras, and the reducer eliminates the field curvature that shows up at the native f/6 ratio. Alan Dyer noted no sign of chromatic aberration in his photographic testing for Sky & Telescope.

What mount does it need?
At under 12 pounds fully loaded (with rings, dovetail, diagonal, and eyepiece), the AT90CFT works well on mid-range mounts like the iOptron CEM26, Sky-Watcher AZ-GTi in EQ mode, or Celestron AVX. For visual only, a sturdy alt-az like the Twilight II or Astro-Tech Voyager is more than enough. The scope’s light weight is one of its strongest selling points for travel imaging setups.

What’s the relationship to the TMB-92?
Thomas Back designed the original TMB-92 Signature Series, which became one of the most sought-after 90mm-class APOs ever made. The AT90CFT carries that design lineage forward Tom’s original design parameters were refined by Roger Ceragioli to take advantage of current glass and coatings. The change from 92mm to 90mm and from f/5.5 to f/6 was made to optimize the optical train for a dedicated 0.8x reducer/flattener. The result is a scope that, in Alan Dyer’s assessment, performs as well as or better than the original.

Optional Accessories

• AT90CFTRF 0.8x Reducer/Field Flattener converts the AT90CFT to 432mm f/4.8 for faster imaging with a flat, corrected field. Dedicated design for the AT90CFT and AT90EDX. 48mm T-thread camera connection.
• Astro-Tech 2″ 99% Reflectivity Dielectric Mirror Diagonal high-reflectivity diagonal for visual observing. 99% dielectric coatings preserve maximum light transmission.
• Astro-Tech Illuminated Multiple Reticle Finder red-dot finder with multiple reticle patterns. Lightweight, easy to align.

Final Thoughts

The AT90CFT exists because there are observers and imagers who want serious APO performance in a package they’ll actually take outside whether that’s the backyard on a Tuesday night or a dark-sky site they flew to with a carry-on. The TMB-92 lineage is real. The 0.95 Strehl guarantee is real. The carbon fiber tube, the dual-speed focuser with Camera Angle Adjuster, the compression ring holders, the padded case all of it is built to make the gap between “wanting to observe” and “actually observing” as small as possible. If you’ve been holding out for a 90mm triplet that performs like a premium APO without the premium-APO weight penalty, this is the one.

Tech Details: