A Celestron X-Cel LX 9mm in the Celestron C9.25 optical tube gives 261x, a 0.23 degree true field and a 0.9 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 9mm in the Celestron C9.25 optical tube: magnification and field

What the Celestron X-Cel LX 9mm does in the Celestron C9.25 optical tube, worked from the published focal lengths and apparent field.

Field of view

ring = 0.23 degrees true
dot = 0.9 mm exit pupil

Computed optics

Magnification
261x2350 mm / 9 mm
True field
0.23 degrees60 deg / 261x
Exit pupil
0.9 mm235 mm / 261x
Max useful mag
555xpublished
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Celestron C9.25 optical tube the Celestron X-Cel LX 9mm gives 261x with a 0.23 degree true field and a 0.9 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 2350 mm divided by 9 mm is 261x. The true field of view is the eyepiece's 60 degree apparent field divided by that magnification, 0.23 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 235 mm over 261x, which is 0.9 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

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Related

Celestron C9.25 optical tube235 mm f/10
Celestron X-Cel LX 9mm9 mm, 60 deg
Best eyepiece for the Celestron C9.25 optical tubeexit-pupil match

Questions and answers

Celestron X-Cel LX 9mm in the Celestron C9.25 optical tube: magnification and field?

Good fit. In the Celestron C9.25 optical tube the Celestron X-Cel LX 9mm gives 261x with a 0.23 degree true field and a 0.9 mm exit pupil, inside the telescope's useful range.