The Sky Rover 90 GPS continues the premium legacy of the GPS lineup. Ninety millimeters of Super ED triplet glass at f/6, delivering 540mm of focal length with the aperture to capture serious deep-sky detail. The SR90GPSFF 1× field flattener is the final piece of your system — the accessory that completes the 90 GPS's optical and mechanical design.
For owners of the 90 GPS, the flattener is the natural complement. It threads directly onto the scope's integrated CAA, maintaining the native 540mm focal length and f/6 ratio. Nothing about the scope's speed or working distance changes. What does change is that the curved focal plane becomes flat, matching the flat silicon of your full-frame sensor. The result: sharp, round, precisely rendered stars from the center of the frame to the corners. For a 90mm f/6 triplet optimized for large-scale deep-sky imaging, the matched flattener transforms a capable scope into a complete, flat-field professional system.
If you’re imaging with the 90 GPS and want clean, usable stars across your frame without cropping the edges, this is the correct flattener for the system.
Flattener, Not Reducer
This is a 1× flattener — it preserves the native focal length and focal ratio of the 90 GPS. You maintain the full 540mm f/6, unchanged. The field of view, exposure times, and image scale all remain the same as the uncorrected scope — you gain what matters: flat, well-corrected stars across the entire sensor from center to corners.
Direct CAA Threading
The 90 GPS's integrated CAA threads the flattener directly to the scope — no adapters, no intermediate accessories, just a clean mechanical connection optimized for optical alignment and stability. This integrated design is part of what makes the 90 GPS a complete system.
Camera Connection
The camera side of the flattener connects to your imaging equipment via standard 48mm T-threads. DSLR and mirrorless cameras 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.
What's Included
- Sky Rover SR90GPSFF 1× field flattener for 90 GPS
Features
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1× field flattener — no focal reduction. Maintains the 90 GPS's native 540mm f/6. Corrects field curvature for flat, sharp stars across the sensor without changing focal length, speed, or working distance.
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Dedicated design for the Sky Rover 90 GPS triplet. Matched to the 90 GPS's optical prescription.
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Direct CAA threading. The flattener threads directly onto the 90 GPS's integrated correcting atmospheric adaptation. No intermediate adapters — just a solid mechanical connection that maintains optical alignment and stability.
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Designed to support full-frame imaging with strong edge performance. The 90mm f/6 triplet is designed for serious deep-sky astrophotography. Adding the matched flattener gives you flat-field performance across full-frame sensors and the image scale needed to capture structure in extended objects.
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Standard camera-side threading. 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.
Frequently Asked Questions
Do I need this flattener for visual observing?
No. Field curvature only affects imaging — your eye naturally accommodates the curved focal plane during visual observation. The flattener is specifically for camera work.
How does this flattener differ from Sky Rover's GPA flatteners?
The GPS flatteners thread directly onto the integrated CAA, giving you a dedicated, mechanically optimized system. GPA flatteners use different connection threads. Each Sky Rover model has a matched flattener designed for its specific optical and mechanical design.
I own a 90 GPS. Is this the right flattener for my scope?
Yes. The SR90GPSFF is designed specifically for the 90 GPS's 540mm focal length, CAA threading, and optical prescription. It's the matched corrector for your system.
What cameras does this work with?
DSLR and mirrorless cameras 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. The flattener is optimized for full-frame sensors but works equally well with APS-C.
What's the back focus distance?
Confirm with Lonnie Wege. The critical measurement is the distance from the flattener's rear threads to the focal plane — ensure adequate spacing for your camera's back-focus design.
Final Thoughts
If you own a Sky Rover 90 GPS, the SR90GPSFF flattener completes the system. You get the triplet's sharpness and light-gathering, the integrated CAA's precision, and now a perfectly flat focal plane matched to your sensor. The 90 GPS was designed as a complete imaging platform, and the matched flattener is the final piece. It's the accessory that turns a very good scope into a professional-grade, field-proven imaging system.
