A Celestron X-Cel LX 7mm in the Celestron C8 optical tube gives 290x, a 0.21 degree true field and a 0.7 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 Celestron C8 optical tube: magnification and field

What the Celestron X-Cel LX 7mm does in the Celestron C8 optical tube, worked from the published focal lengths and apparent field.

Field of view

ring = 0.21 degrees true
dot = 0.7 mm exit pupil

Computed optics

Magnification
290x2032 mm / 7 mm
True field
0.21 degrees60 deg / 290x
Exit pupil
0.7 mm203 mm / 290x
Max useful mag
480xpublished
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Celestron C8 optical tube the Celestron X-Cel LX 7mm gives 290x with a 0.21 degree true field and a 0.7 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 2032 mm divided by 7 mm is 290x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.21 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 203 mm over 290x, which is 0.7 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

Celestron C8 optical tube203 mm f/10
Celestron X-Cel LX 7mm7 mm, 60 deg
Best eyepiece for the Celestron C8 optical tubeexit-pupil match

Questions and answers

Celestron X-Cel LX 7mm in the Celestron C8 optical tube: magnification and field?

Good fit. In the Celestron C8 optical tube the Celestron X-Cel LX 7mm gives 290x with a 0.21 degree true field and a 0.7 mm exit pupil, inside the telescope's useful range.