Optical reference
Celestron C11 optical tube: aperture, focal length and eyepiece fit
What the Celestron C11 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 C11 optical tube | 467x | 0.11 deg |
| Tele Vue 20mm Plossl in the Celestron C11 optical tube | 140x | 0.36 deg |
The C11 is a 280 mm f/10 SCT, a large-aperture tube that still fits on a good German equatorial. Its 2800 mm focal length is long, so a focal reducer is common for deep-sky imaging, while visual planetary detail is its natural strength.
Because magnification is the telescope's 2800 mm focal length divided by the eyepiece focal length, a 25 mm eyepiece gives 112x here and a 10 mm eyepiece gives 280x. The highest useful magnification is the published 660x, 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.