Optical reference
Celestron C9.25 optical tube: aperture, focal length and eyepiece fit
What the Celestron C9.25 optical tube measures, the magnification and true field each eyepiece produces in it, and the barrel, mount payload and camera adapter that fit.
Published specifications
Eyepiece ladder
2 pairings| Pairing | Magnification | True field |
|---|---|---|
| Celestron Omni 6mm Plossl in the Celestron C9.25 optical tube | 392x | 0.13 deg |
| Tele Vue 20mm Plossl in the Celestron C9.25 optical tube | 118x | 0.43 deg |
The C9.25 is a 235 mm f/10 SCT with a slightly slower primary than the rest of the line, which many observers credit for its sharp planetary images. Its 2350 mm focal length suits high-resolution lunar, planetary and double-star work.
Because magnification is the telescope's 2350 mm focal length divided by the eyepiece focal length, a 25 mm eyepiece gives 94x here and a 10 mm eyepiece gives 235x. The highest useful magnification is the published 555x, beyond which the image dims and softens without showing more detail.
The focuser takes 2 in eyepieces, so long 2 in wide-field eyepieces such as the Omni 56 mm fit as well as 1.25 in ones.