The AT80EDT is one of our most popular grab-and-go imaging refractors — 80mm of FK-61 triplet glass at 480mm f/6, compact enough for airline travel and light enough for small mounts, but sharp enough for serious deep-sky work. At f/6, the field curves. Stars in the center are tight. Stars toward the edges stretch. That's not a flaw in the scope — it's what any uncorrected refractor does to a flat sensor. A dedicated field flattener fixes it.
The AT80EDTFF is a 1× flattener designed specifically for the AT80EDT. It doesn't reduce the focal length or change the focal ratio — you keep the full 480mm at f/6. What it does is flatten the field so stars are round and sharp across your sensor. The AT80EDT delivers the light. The flattener makes sure that light lands correctly on the chip.
Sensor Coverage — What to Expect
The AT80EDTFF delivers excellent correction across APS-C sensors (roughly 22×15mm) and smaller — round, tight stars from center to edge. On full-frame sensors (36×24mm), you may see some residual curvature at the extreme corners. This is an 80mm scope at f/6, and the corrected image circle has its limits. For most APS-C imaging — which is the sensor size most commonly paired with an 80mm refractor — the flattener does exactly what it needs to do. If you're planning to image full-frame with the AT80EDT, consider testing your specific camera to see if the corner performance meets your standards, or use cropping in processing.
Why 1× Instead of a Reducer?
We also make a 0.8× reducer/field flattener for the AT80EDT. That drops the focal length to 384mm at f/4.8 — faster exposures and a wider field, but a different image scale and a different set of targets that frame well. The 1× flattener is for imagers who want the AT80EDT's native 480mm focal length. At 480mm, mid-size targets — the Horsehead and Flame region, the Pleiades, the Orion Nebula complex, galaxy groups — have enough scale to show detail without being so large they clip the field. The flattener keeps the image scale and just fixes the field curvature.
Connection and Installation
The scope side of the AT80EDTFF has an M63 threaded connection that threads directly onto the AT80EDT focuser drawtube — or onto the Camera Angle Adjuster if you're using the rotation feature. No barrel insert. No adapter. Just threads — secure, repeatable, and square to the optical axis every time you set up.
The camera side terminates in 48mm T-threads. DSLR and mirrorless bodies connect via a T-ring for your specific camera mount (sold separately). Dedicated CMOS and CCD astronomy cameras typically have 48mm T-threads built in and connect directly without a T-ring.
Back focus is 55mm from the flattener's shoulder to the sensor. ZWO filter wheel + OAG + camera stacks are designed for 55mm and bolt together directly. A DSLR with a standard T-ring typically hits the spacing naturally. Dedicated cameras with different flange distances may need 48mm spacer rings to dial it in.
Inline Filter Thread
The top section of the flattener body unscrews, exposing a 2" filter thread on the lower section. Thread in a light pollution, UHC, or narrowband filter without adding a separate filter drawer or filter wheel. For one-shot color camera setups with a single broadband or dual-narrowband filter, this keeps the imaging train short and the back focus math simple.
Features
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1× dedicated field flattener — no focal reduction. Maintains the AT80EDT's native 480mm f/6. Flattens the field for round stars across your sensor without changing image scale or field of view.
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Excellent APS-C coverage. Corrects field curvature across APS-C (roughly 22×15mm) sensors and smaller with round stars from center to edge. Full-frame sensors may show some residual curvature at the extreme corners.
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Optically matched to the AT80EDT. Designed for the AT80EDT's specific focal length and field curvature. Delivers better correction than generic flatteners because the optics are tuned to this scope.
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M63 threaded scope-side connection. Threads directly to the AT80EDT focuser drawtube or Camera Angle Adjuster. No barrel insert, no adapter — secure, tilt-free positioning every session.
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48mm T-thread camera connection. DSLR and mirrorless bodies connect via a T-ring (sold separately); dedicated CMOS/CCD astronomy cameras attach directly — 48mm T-threads are standard on most.
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55mm back focus. From the flattener shoulder to the sensor. Standard DSLR T-ring spacing typically hits this naturally. ZWO filter wheel + OAG + camera stacks are designed for 55mm.
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2" inline filter thread. Unscrew the top section to expose a 2" filter thread for inline filter use without a filter drawer.
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Fully multi-coated optics. Maximizes light transmission and minimizes internal reflections.
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Lightweight at 9.5 oz. Minimal impact on balance or focuser load.
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Protective covers included. Threaded covers for both ends.
Observing Tip
The AT80EDT at 480mm f/6 is a natural widefield imaging scope, and one of its strengths is that it frames larger targets well at a fast focal ratio. With the 1× flattener and an APS-C camera, you've got a flat, corrected field at 480mm — enough focal length for the Rosette Nebula, the Heart and Soul pair, the Lagoon and Trifid region, and similar mid-size targets to fill the frame with detail. If you're running a one-shot color camera with a single broadband or dual-narrowband filter, thread the filter into the flattener's 2" thread and skip the filter drawer. Fewer connections, less tilt risk, simpler setup.
Frequently Asked Questions
What's the difference between this and the 0.8× reducer/flattener?
The AT80EDTFF is a 1× flattener — it corrects field curvature without changing focal length. You keep 480mm at f/6. The 0.8× reducer/flattener reduces to 384mm at f/4.8 — faster exposures (56% more light per pixel), wider field, but different image scale. Choose the 1× for more image scale on smaller targets. Choose the 0.8× for wider fields and shorter exposures.
Will this cover a full-frame sensor?
The flattener performs best with APS-C sensors and smaller. On full-frame chips, you may see some residual field curvature at the extreme corners. This is a function of the 80mm aperture — the corrected image circle is large enough for APS-C but reaches its limits on full frame. If you need guaranteed full-frame flat-field coverage, consider the AT115EDT or AT130EDT with their respective 1× flatteners.
Do I need a T-ring?
If you're using a DSLR or mirrorless camera, yes — you need a T-ring for your specific camera mount (sold separately). Dedicated CMOS and CCD astronomy cameras typically have 48mm T-threads built in and connect directly.
Can I use a filter wheel with this?
Yes. A ZWO filter wheel + OAG + camera stack is designed to hit 55mm back focus. Thread the flattener onto the scope, attach the filter wheel to the 48mm T-threads, and the system is at the correct spacing.
How critical is the 55mm back focus?
Very. If the spacing from the flattener's shoulder to your sensor is off by more than a couple of millimeters, you'll see elongated stars toward the edges. M48 spacer rings in 1mm, 2mm, and 5mm increments let you dial it in. Measure once, mark your configuration, and it stays consistent.
Final Thoughts
The AT80EDT is a compact, travel-friendly imaging refractor with a loyal following. The AT80EDTFF gives it a flat field at the full 480mm f/6 — round stars from center to edge across APS-C sensors, no compromise on focal length or image scale. If you're imaging with the AT80EDT and an APS-C camera, this is the flattener that was matched to your scope. Thread it on, set the spacing, and shoot.
