Optical reference
Sky-Watcher Classic 250P (10-inch Dobsonian): aperture, focal length and eyepiece fit
What the Sky-Watcher Classic 250P (10-inch Dobsonian) 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 |
|---|---|---|
| Tele Vue 3.5mm Nagler Type 6 in the Sky-Watcher Classic 250P (10-inch Dobsonian) | 343x | 0.24 deg |
| Celestron Omni 9mm Plossl in the Sky-Watcher Classic 250P (10-inch Dobsonian) | 133x | 0.38 deg |
The Classic 250P is a fast 254 mm f/4.7 Dobsonian: 10 in of aperture at a 1200 mm focal length. It gathers far more light than an 8 in for fainter deep-sky objects, and its fast focal ratio makes long eyepieces give very wide, low-power fields.
Because magnification is the telescope's 1200 mm focal length divided by the eyepiece focal length, a 25 mm eyepiece gives 48x here and a 10 mm eyepiece gives 120x. The highest useful magnification is about 508x (roughly twice the aperture in millimetres), 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.