A Celestron Omni 9mm Plossl in the Celestron Astro Fi 102 gives 147x, a 0.34 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 Omni 9mm Plossl in the Celestron Astro Fi 102: magnification and field

What the Celestron Omni 9mm Plossl does in the Celestron Astro Fi 102, worked from the published focal lengths and apparent field.

Field of view

ring = 0.34 degrees true
dot = 0.7 mm exit pupil

Computed optics

Magnification
147x1325 mm / 9 mm
True field
0.34 degrees50 deg / 147x
Exit pupil
0.7 mm102 mm / 147x
Max useful mag
241xpublished
Barrel match
1.25 in eyepiece in a 1.25 in focuser
Fits

Good fit. In the Celestron Astro Fi 102 the Celestron Omni 9mm Plossl gives 147x with a 0.34 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: 1325 mm divided by 9 mm is 147x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.34 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 102 mm over 147x, which is 0.7 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

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Related

Celestron Astro Fi 102102 mm f/13
Celestron Omni 9mm Plossl9 mm, 50 deg
Best eyepiece for the Celestron Astro Fi 102exit-pupil match

Questions and answers

Celestron Omni 9mm Plossl in the Celestron Astro Fi 102: magnification and field?

Good fit. In the Celestron Astro Fi 102 the Celestron Omni 9mm Plossl gives 147x with a 0.34 degree true field and a 0.7 mm exit pupil, inside the telescope's useful range.