A Celestron Omni 56mm Plossl in the Sky-Watcher Evostar 80ED gives 11x, a 4.39 degree true field and a 7.5 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Celestron Omni 56mm Plossl in the Sky-Watcher Evostar 80ED: magnification and field

What the Celestron Omni 56mm Plossl does in the Sky-Watcher Evostar 80ED, worked from the published focal lengths and apparent field.

Field of view

ring = 4.39 degrees true
dot = 7.5 mm exit pupil

Computed optics

Magnification
11x600 mm / 56 mm
True field
4.39 degrees47 deg / 11x
Exit pupil
7.5 mm80 mm / 11x
Max useful mag
189xpublished
Barrel match
2 in eyepiece in a 2 in focuser
Needs adapter

Works, but the 7.5 mm exit pupil is wider than a dark-adapted pupil of about 7 mm, so the outer light is wasted and the sky background looks brighter. Fine for framing, but a slightly shorter eyepiece uses the aperture better.

Magnification is the telescope focal length divided by the eyepiece focal length: 600 mm divided by 56 mm is 11x. The true field of view is the eyepiece's 47 degree apparent field divided by that magnification, 4.39 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 80 mm over 11x, which is 7.5 mm. That makes this a low-power, wide-field and deep-sky setting.

The eyepiece to buy

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Related

Sky-Watcher Evostar 80ED80 mm f/7.5
Celestron Omni 56mm Plossl56 mm, 47 deg
Best eyepiece for the Sky-Watcher Evostar 80EDexit-pupil match

Questions and answers

Celestron Omni 56mm Plossl in the Sky-Watcher Evostar 80ED: magnification and field?

Works, but the 7.5 mm exit pupil is wider than a dark-adapted pupil of about 7 mm, so the outer light is wasted and the sky background looks brighter. Fine for framing, but a slightly shorter eyepiece uses the aperture better.