A Tele Vue 10mm Ethos in the Celestron C5 optical tube gives 125x, a 0.8 degree true field and a 1 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 C5 optical tube: magnification and field

What the Tele Vue 10mm Ethos does in the Celestron C5 optical tube, worked from the published focal lengths and apparent field.

Field of view

ring = 0.8 degrees true
dot = 1 mm exit pupil

Computed optics

Magnification
125x1250 mm / 10 mm
True field
0.8 degrees100 deg / 125x
Exit pupil
1 mm127 mm / 125x
Max useful mag
295xpublished
Barrel match
1.25 in eyepiece in a 1.25 in focuser
Fits

Good fit. In the Celestron C5 optical tube the Tele Vue 10mm Ethos gives 125x with a 0.8 degree true field and a 1 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1250 mm divided by 10 mm is 125x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 0.8 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 127 mm over 125x, which is 1 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

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Related

Celestron C5 optical tube127 mm f/10
Tele Vue 10mm Ethos10 mm, 100 deg
Best eyepiece for the Celestron C5 optical tubeexit-pupil match

Questions and answers

Tele Vue 10mm Ethos in the Celestron C5 optical tube: magnification and field?

Good fit. In the Celestron C5 optical tube the Tele Vue 10mm Ethos gives 125x with a 0.8 degree true field and a 1 mm exit pupil, inside the telescope's useful range.