A Celestron X-Cel LX 7mm in the Sky-Watcher Evostar 100ED gives 129x, a 0.47 degree true field and a 0.8 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 7mm in the Sky-Watcher Evostar 100ED: magnification and field

What the Celestron X-Cel LX 7mm does in the Sky-Watcher Evostar 100ED, worked from the published focal lengths and apparent field.

Field of view

ring = 0.47 degrees true
dot = 0.8 mm exit pupil

Computed optics

Magnification
129x900 mm / 7 mm
True field
0.47 degrees60 deg / 129x
Exit pupil
0.8 mm100 mm / 129x
Max useful mag
236xpublished
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Evostar 100ED the Celestron X-Cel LX 7mm gives 129x with a 0.47 degree true field and a 0.8 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 900 mm divided by 7 mm is 129x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.47 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 100 mm over 129x, which is 0.8 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

Shop Celestron X-Cel LX 7mm on AmazonaffiliateFind Celestron X-Cel LX 7mm on eBayaffiliate

Related

Sky-Watcher Evostar 100ED100 mm f/9
Celestron X-Cel LX 7mm7 mm, 60 deg
Best eyepiece for the Sky-Watcher Evostar 100EDexit-pupil match

Questions and answers

Celestron X-Cel LX 7mm in the Sky-Watcher Evostar 100ED: magnification and field?

Good fit. In the Sky-Watcher Evostar 100ED the Celestron X-Cel LX 7mm gives 129x with a 0.47 degree true field and a 0.8 mm exit pupil, inside the telescope's useful range.