Optical reference

Sky-Watcher Classic 200P (8-inch Dobsonian): aperture, focal length and eyepiece fit

What the Sky-Watcher Classic 200P (8-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

Aperture
203 mm (7.99 in)
Focal length
1200 mm
Focal ratio
f/5.9
Optical design
Newtonian reflector (parabolic primary)
Focuser / eyepiece barrel
2 in Crayford focuser with a 1.25 in adapter
Mount
Manual Dobsonian base
Highest useful magnification (2x aperture rule)
about 406x

Eyepiece ladder

2 pairings

The Classic 200P is the archetypal 8 in f/5.9 Dobsonian: 203 mm of aperture at a 1200 mm focal length on a simple, stable base. Its 2 in focuser takes long 2 in eyepieces for the widest possible 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 406x (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.