A Celestron X-Cel LX 18mm in the Sky-Watcher Skymax 102 gives 72x, a 0.83 degree true field and a 1.4 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 18mm in the Sky-Watcher Skymax 102: magnification and field

What the Celestron X-Cel LX 18mm does in the Sky-Watcher Skymax 102, worked from the published focal lengths and apparent field.

Field of view

ring = 0.83 degrees true
dot = 1.4 mm exit pupil

Computed optics

Magnification
72x1300 mm / 18 mm
True field
0.83 degrees60 deg / 72x
Exit pupil
1.4 mm102 mm / 72x
Max useful mag
about 204x2x aperture
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Skymax 102 the Celestron X-Cel LX 18mm gives 72x with a 0.83 degree true field and a 1.4 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1300 mm divided by 18 mm is 72x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.83 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 102 mm over 72x, which is 1.4 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

Shop Celestron X-Cel LX 18mm on AmazonaffiliateFind Celestron X-Cel LX 18mm on eBayaffiliate

Related

Sky-Watcher Skymax 102102 mm f/12.7
Celestron X-Cel LX 18mm18 mm, 60 deg
Best eyepiece for the Sky-Watcher Skymax 102exit-pupil match

Questions and answers

Celestron X-Cel LX 18mm in the Sky-Watcher Skymax 102: magnification and field?

Good fit. In the Sky-Watcher Skymax 102 the Celestron X-Cel LX 18mm gives 72x with a 0.83 degree true field and a 1.4 mm exit pupil, inside the telescope's useful range.