A Celestron X-Cel LX 12mm in the Sky-Watcher Classic 250P (10-inch Dobsonian) gives 100x, a 0.6 degree true field and a 2.5 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Celestron X-Cel LX 12mm in the Sky-Watcher Classic 250P (10-inch Dobsonian): magnification and field

What the Celestron X-Cel LX 12mm does in the Sky-Watcher Classic 250P (10-inch Dobsonian), worked from the published focal lengths and apparent field.

Field of view

ring = 0.6 degrees true
dot = 2.5 mm exit pupil

Computed optics

Magnification
100x1200 mm / 12 mm
True field
0.6 degrees60 deg / 100x
Exit pupil
2.5 mm254 mm / 100x
Max useful mag
about 508x2x aperture
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Classic 250P (10-inch Dobsonian) the Celestron X-Cel LX 12mm gives 100x with a 0.6 degree true field and a 2.5 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1200 mm divided by 12 mm is 100x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.6 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 254 mm over 100x, which is 2.5 mm. That makes this a medium-power general setting.

The eyepiece to buy

Shop Celestron X-Cel LX 12mm on AmazonaffiliateFind Celestron X-Cel LX 12mm on eBayaffiliate

Related

Sky-Watcher Classic 250P (10-inch Dobsonian)254 mm f/4.7
Celestron X-Cel LX 12mm12 mm, 60 deg
Best eyepiece for the Sky-Watcher Classic 250P (10-inch Dobsonian)exit-pupil match

Questions and answers

Celestron X-Cel LX 12mm in the Sky-Watcher Classic 250P (10-inch Dobsonian): magnification and field?

Good fit. In the Sky-Watcher Classic 250P (10-inch Dobsonian) the Celestron X-Cel LX 12mm gives 100x with a 0.6 degree true field and a 2.5 mm exit pupil, inside the telescope's useful range.