A Celestron Omni 9mm Plossl in the Sky-Watcher Evostar 80ED gives 67x, a 0.75 degree true field and a 1.2 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 Sky-Watcher Evostar 80ED: magnification and field

What the Celestron Omni 9mm Plossl does in the Sky-Watcher Evostar 80ED, worked from the published focal lengths and apparent field.

Field of view

ring = 0.75 degrees true
dot = 1.2 mm exit pupil

Computed optics

Magnification
67x600 mm / 9 mm
True field
0.75 degrees50 deg / 67x
Exit pupil
1.2 mm80 mm / 67x
Max useful mag
189xpublished
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Evostar 80ED the Celestron Omni 9mm Plossl gives 67x with a 0.75 degree true field and a 1.2 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 600 mm divided by 9 mm is 67x. The true field of view is the eyepiece's 50 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, 80 mm over 67x, which is 1.2 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

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Related

Sky-Watcher Evostar 80ED80 mm f/7.5
Celestron Omni 9mm Plossl9 mm, 50 deg
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Questions and answers

Celestron Omni 9mm Plossl in the Sky-Watcher Evostar 80ED: magnification and field?

Good fit. In the Sky-Watcher Evostar 80ED the Celestron Omni 9mm Plossl gives 67x with a 0.75 degree true field and a 1.2 mm exit pupil, inside the telescope's useful range.