The AT102EDL is a versatile doublet APO at 714mm f/7 — plenty of focal length for mid-range targets and sharp enough for visual work on any given night. But when you attach a camera, the field curvature that's invisible at the eyepiece becomes obvious in your images. Stars that are tight in the center soften into small streaks near the corners. The AT102EDLRF corrects that curvature and reduces the focal length to 571mm f/5.6 — a 56% increase in photographic speed — so you get flat fields, round stars, and shorter exposures in one piece of glass.
Designed for One Scope
This reducer/flattener is computed specifically for the field curvature of the Astro-Tech AT102EDL 102mm f/7 doublet APO refractor. A generic 0.8x reducer will shorten the focal length, but it won't match the correction to your scope's specific optical profile. This one does. It may thread into other f/7 refractors with a 2.5-inch focuser, but optical performance outside the AT102EDL is not guaranteed.
How It Connects
The scope side threads into the focuser drawtube using M63×1 metric threads — a solid, repeatable connection with no compression ring and no play. The camera side has standard 48mm T-threads, connecting to a T-ring for DSLR and mirrorless bodies, or directly to dedicated CMOS and CCD astronomy cameras, which come with 48mm T-threads built in.
Back focus is 55mm from the shoulder of the reducer to the image plane. That's the standard DSLR spacing — a T-ring and camera body will put you at the correct distance without spacers. For dedicated astronomy cameras, measure your camera's back focus specification and add spacers if needed to reach 55mm.
What's Included
- Astro-Tech AT102EDLRF 0.8x reducer/field flattener
- Slip-on rubber dust cover for 48mm T-threads (camera side)
- Slip-on dust cover for 2" scope-side barrel
Features
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0.8x focal reduction — Converts the AT102EDL from 714mm f/7 to 571mm f/5.6. That's a 56% increase in photographic speed — the same signal-to-noise ratio in roughly two-thirds the exposure time.
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Field flattening — Corrects the native field curvature of the AT102EDL so stars stay round and sharp all the way to the corners of your imaging chip.
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Fully multi-coated optics — Minimizes reflections and maximizes light transmission through the reducer elements.
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M63×1 scope-side thread — Threads securely into the focuser drawtube. No set screws, no wobble, no shift between sessions.
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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 — Standard DSLR spacing. No spacers needed for most DSLR setups. Dedicated astronomy cameras may require spacers to reach the correct distance.
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Compact and lightweight — 8 ounces. Adds minimal weight to your imaging train.
Imaging Tip
When you first set up the AT102EDLRF, shoot a short test exposure of a star field and inspect the corners at 100% zoom. If stars are elongated radially (pointing away from center), you're too far from the reducer — remove a spacer or check your T-ring stack. If stars are elongated tangentially (perpendicular to the radial direction), you're too close. The 55mm specification is measured from the shoulder of the reducer, not the rear element — make sure you're measuring from the right reference point.
FAQ
Will this work with my AT125EDL or AT150EDL?
No. Each EDL scope has its own dedicated reducer matched to its specific field curvature. The AT125EDL uses the AT125EDLRF, and the AT150EDL uses the AT150EDLRF. They are not interchangeable.
Can I use this visually?
The reducer is designed for prime-focus astrophotography. It will not reach focus with an eyepiece and is not intended for visual use.
Do I need a T-ring?
DSLR and mirrorless cameras connect via a T-ring for your specific mount (sold separately). Dedicated CMOS and CCD astronomy cameras typically have 48mm T-threads built in and connect directly without a T-ring.
What sensors have been tested with this reducer?
Owners report sharp stars to the edges of 4/3-format sensors (like the ASI-294mc) at the specified 55mm back focus. Results on larger APS-C and full-frame sensors will depend on precise spacing — test and adjust before committing to long integration times.
Final Thoughts
If you're imaging through the AT102EDL, this is the reducer that was built for it. It flattens the field, speeds the system to f/5.6, and threads in with a secure M63 connection that holds position between sessions. At 8 ounces, it barely changes the balance of your imaging train. The AT102EDL is already one of the most capable doublets in its aperture class — the AT102EDLRF turns it into a proper imaging platform with flat fields and faster exposures.
