A Tele Vue 21mm Ethos in the Celestron NexStar Evolution 6 gives 71x, a 1.4 degree true field and a 2.1 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Tele Vue 21mm Ethos in the Celestron NexStar Evolution 6: magnification and field

What the Tele Vue 21mm Ethos does in the Celestron NexStar Evolution 6, worked from the published focal lengths and apparent field.

Field of view

ring = 1.4 degrees true
dot = 2.1 mm exit pupil

Computed optics

Magnification
71x1500 mm / 21 mm
True field
1.4 degrees100 deg / 71x
Exit pupil
2.1 mm150 mm / 71x
Max useful mag
354xpublished
Barrel match
2 in eyepiece in a 2 in focuser
Fits

Good fit. In the Celestron NexStar Evolution 6 the Tele Vue 21mm Ethos gives 71x with a 1.4 degree true field and a 2.1 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1500 mm divided by 21 mm is 71x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 1.4 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 150 mm over 71x, which is 2.1 mm. That makes this a medium-power general setting.

The eyepiece to buy

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Related

Celestron NexStar Evolution 6150 mm f/10
Tele Vue 21mm Ethos21 mm, 100 deg
Best eyepiece for the Celestron NexStar Evolution 6exit-pupil match

Questions and answers

Tele Vue 21mm Ethos in the Celestron NexStar Evolution 6: magnification and field?

Good fit. In the Celestron NexStar Evolution 6 the Tele Vue 21mm Ethos gives 71x with a 1.4 degree true field and a 2.1 mm exit pupil, inside the telescope's useful range.