Celestron EdgeHD 9.25"

Worth knowing before you buy

How critical is back-focus distance for imaging, and will my camera work without an external focuser?

EdgeHD requires precise back-focus spacing (within a few millimeters) for proper field correction across large sensors, unlike the Meade ACF which is less sensitive to this. The primary focuser works well for autofocus with proper technique, but many users add external focusers for additional flexibility and to allow a fully rigid imaging train attachment.

Will the EdgeHD give me a flat, well-corrected field edge-to-edge for full-frame imaging?

The EdgeHD is corrected to a 42mm image circle and delivers consistent sharpness across that field, but shows vignetting (40-50% light fall-off) at the very edge on full-frame sensors. For APS-C sensors it performs excellently; for full-frame work you'll need to either accept vignetting or use the Celestron EdgeHD focal reducer, which is expensive but maintains the back-focus distance.

How does the EdgeHD compare optically to the Meade ACF?

Both are excellent scopes with very good optics. The EdgeHD has a slight edge in contrast and field flatness due to correction for both coma and field curvature, while the ACF corrects only coma but is less sensitive to back-focus errors.

Are there any issues with the corrector plate or internal baffles?

One user reported corrector lenses falling out of an 11-inch EdgeHD, which raised concerns about internal design. Members also note that the baffle tube is positioned very close to the visual back threads, requiring precise component spacing for optimal correction.

Can I use generic focal reducers, or do I need the Celestron EdgeHD reducer?

A generic focal reducer will work but introduces aberrations specific to the EdgeHD design that may not be optimally corrected. The Celestron EdgeHD focal reducer is specifically designed for the scope's aberrations but is expensive; however, it preserves back-focus distance and image circle unlike generic reducers.

How does this scope compare for visual observation of planets and deep-sky objects?

Members report excellent contrast, sharpness, and a vibrant 'pop' to views through the EdgeHD, with a very flat field that benefits visual observers. The nearly flat field is praised as being comparable to high-end binoculars; for planets specifically, the smaller secondary mirror gives a slight brightness advantage over the ACF.