A Celestron X-Cel LX 18mm in the Celestron C14 optical tube gives 217x, a 0.28 degree true field and a 1.6 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 Celestron C14 optical tube: magnification and field

What the Celestron X-Cel LX 18mm does in the Celestron C14 optical tube, worked from the published focal lengths and apparent field.

Field of view

ring = 0.28 degrees true
dot = 1.6 mm exit pupil

Computed optics

Magnification
217x3910 mm / 18 mm
True field
0.28 degrees60 deg / 217x
Exit pupil
1.6 mm356 mm / 217x
Max useful mag
840xpublished
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Celestron C14 optical tube the Celestron X-Cel LX 18mm gives 217x with a 0.28 degree true field and a 1.6 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 3910 mm divided by 18 mm is 217x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.28 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 356 mm over 217x, which is 1.6 mm. That makes this a medium-power general setting.

The eyepiece to buy

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

Related

Celestron C14 optical tube356 mm f/11
Celestron X-Cel LX 18mm18 mm, 60 deg
Best eyepiece for the Celestron C14 optical tubeexit-pupil match

Questions and answers

Celestron X-Cel LX 18mm in the Celestron C14 optical tube: magnification and field?

Good fit. In the Celestron C14 optical tube the Celestron X-Cel LX 18mm gives 217x with a 0.28 degree true field and a 1.6 mm exit pupil, inside the telescope's useful range.