A Tele Vue 10mm Ethos in the Celestron Astro Fi 102 gives 132x, a 0.75 degree true field and a 0.8 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Tele Vue 10mm Ethos in the Celestron Astro Fi 102: magnification and field

What the Tele Vue 10mm Ethos does in the Celestron Astro Fi 102, worked from the published focal lengths and apparent field.

Field of view

ring = 0.75 degrees true
dot = 0.8 mm exit pupil

Computed optics

Magnification
132x1325 mm / 10 mm
True field
0.75 degrees100 deg / 132x
Exit pupil
0.8 mm102 mm / 132x
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 Tele Vue 10mm Ethos gives 132x with a 0.75 degree true field and a 0.8 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 10 mm is 132x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 0.75 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 102 mm over 132x, which is 0.8 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
Tele Vue 10mm Ethos10 mm, 100 deg
Best eyepiece for the Celestron Astro Fi 102exit-pupil match

Questions and answers

Tele Vue 10mm Ethos in the Celestron Astro Fi 102: magnification and field?

Good fit. In the Celestron Astro Fi 102 the Tele Vue 10mm Ethos gives 132x with a 0.75 degree true field and a 0.8 mm exit pupil, inside the telescope's useful range.