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."
There's a telescope problem that no amount of aperture solves: the one where you leave it at home because it's too heavy, too long, or too much trouble to set up at a dark site three hours away. You own a beautiful instrument, and it sits in a closet because the logistics won out. The AT90CFT was built for people who got tired of that tradeoff.
At 90mm f/6, the AT90CFT packs a triplet apochromatic refractor with FCD-100 ED glass into an 18-inch carbon fiber tube that weighs under 12 pounds with rings and dovetail. It fits in a padded soft case you can carry on your shoulder. You can set it up on a lightweight mount in minutes, observe or image for hours, and pack it out without needing a hand truck. And the views through it will make you forget you're looking through a 90mm scope.
The Design
Thomas Back laid the foundation for this telescope when he designed the TMB-92 Signature Series — a scope that still commands serious money on the used market. The design sat in our vault for years until we sent it to Roger Ceragioli, who studied it, updated it for current glass and coatings, and worked with our manufacturer to squeeze every fraction of performance out of the triplet configuration. The result is a guaranteed 0.95 Strehl ratio — meaning these optics are performing at 95% or better of theoretical perfection. Alan Dyer, reviewing the AT90CFT in Sky & Telescope, called it a worthy successor to the TMB-92 and a desert-island telescope.
The Optics
The triplet objective uses an FCD-100 ED center element flanked by two mating elements, fully multicoated on all surfaces. Chromatic aberration is essentially absent — Alan Dyer reported no sign of longitudinal CA in his testing, and the color correction holds from visual observing through full-frame astrophotography. Contrast is exceptional, aided by knife-edge internal baffles and blackened lens edges that kill stray reflections before they reach your eye or sensor. This is a scope that shows you the sky, not the optics.
Built to Travel
The carbon fiber tube keeps the weight down and looks sharp doing it — matte black metal trim and red CNC-machined rings give the AT90CFT a fit and finish that punches well above its price class. The retractable dew shield collapses the scope to just 18 inches for storage and transport. The included padded soft case (21" × 11" × 10") has a carry handle, shoulder strap, and five cutout spaces for the diagonal, reducer, and other accessories. You pack the scope, grab the case, and go.
The Focuser
The 2.5-inch dual-speed rack and pinion focuser has two coarse knobs and a concentric 10:1 fine-focus knob — ribbed for cold-weather use with gloves. The precision is good enough for high-magnification planetary work and critical imaging focus with a Bahtinov mask. A built-in Camera Angle Adjuster lets you rotate your camera's framing without removing anything from the optical train. The focuser drawtube ends in a 2-inch compression ring eyepiece holder (non-marring twist lock), and a 1.25-inch adapter is included. A Vixen finder shoe is pre-installed on the focuser body.
What's Included
- AT90CFT optical tube assembly with retractable dew shield
- CNC tube rings with integrated carry handle
- Vixen-style dovetail plate
- 2" compression ring eyepiece holder
- 1.25" compression ring adapter
- Slip-on metal dust cap
- Vixen finder shoe (installed on focuser)
- 21" × 11" × 10" padded soft case with carry handle and shoulder strap
Features
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FCD-100 Triplet APO Optics: ED center element with two mating elements delivers color-free, high-contrast views across the visual and photographic spectrum. Guaranteed 0.95 Strehl ratio.
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Carbon Fiber Tube: Lightweight, thermally stable, and strikingly finished in black carbon fiber with matte black metal trim. Keeps the OTA under 12 pounds fully rigged.
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18-Inch Travel Length: Retractable dew shield collapses the tube to just 18 inches — small enough to fit carry-on overhead or slip into a backpack case.
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2.5" Dual-Speed Focuser: Rack and pinion with 10:1 fine-focus knob. Ribbed knobs work with gloves. Smooth, precise, and backlash-free for critical planetary and imaging focus.
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Built-In Camera Angle Adjuster: Rotate your camera's framing without removing the imaging train from the focuser. One less thing to fuss with on a cold night.
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Compression Ring Holders: Non-marring twist-lock compression rings on both 2" and 1.25" holders protect your diagonals and accessories from thumbscrew scratches.
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Knife-Edge Internal Baffles: Combined with blackened lens edges, these baffles suppress stray light and maximize contrast on both planetary detail and faint deep-sky structure.
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Fully Multicoated Optics: Latest antireflection coatings on all glass-to-air surfaces. Light transmission is high enough that the optics practically disappear when viewed from the front.
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CNC Tube Rings with Handle: Hinged rings for quick setup, integrated carry handle on top, Vixen dovetail on the bottom. Solid, well-machined, and ready to go.
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Padded Soft Case: Custom-fit 21" × 11" × 10" case with foam cutouts for the OTA and accessories, carry handle, and shoulder strap. The scope ships in this case.
Under the Night Sky
Ninety millimeters of triplet APO will show you more than most people expect. On the Moon, this scope delivers razor-sharp views of craters, rilles, and the subtle shadow play along the terminator — the kind of detail that makes you lean in and forget you're looking through glass at all. Jupiter shows defined cloud belts with hints of festoon detail on a steady night at 135–180x. Saturn's rings are cleanly separated from the disk with the Cassini Division visible at 150x under good seeing. Mars at opposition will show the dark surface markings and a polar cap. None of it will show a trace of false color.
For deep sky, the 540mm focal length and f/6 speed put you in a versatile sweet spot. With a 28mm wide-field eyepiece, you get roughly a 2.9-degree true field — wide enough to frame the Pleiades with room to spare or sweep through the Sagittarius Milky Way. With the dedicated 0.8x reducer (sold separately), the system drops to 432mm at f/4.8 — fast enough for serious one-shot-color imaging of extended nebulae and galaxy groups. M81 and M82 will pop cleanly in the same field. The Veil Nebula is a rewarding target with a narrowband filter. And the North America Nebula fills the frame on an APS-C sensor at the reduced focal length.
This is a scope that doesn't ask you to choose between visual and imaging, or between planetary and deep sky. It does all of it well, in a package you can actually take with you.
Community Says
"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 20–30 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
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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.
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Astro-Tech 2" 99% Reflectivity Dielectric Mirror Diagonal — high-reflectivity diagonal for visual observing. 99% dielectric coatings preserve maximum light transmission.
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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.
