A Celestron Omni 9mm Plossl in the Sky-Watcher Skymax 150 gives 200x, a 0.25 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

Celestron Omni 9mm Plossl in the Sky-Watcher Skymax 150: magnification and field

What the Celestron Omni 9mm Plossl does in the Sky-Watcher Skymax 150, worked from the published focal lengths and apparent field.

Field of view

ring = 0.25 degrees true
dot = 0.8 mm exit pupil

Computed optics

Magnification
200x1800 mm / 9 mm
True field
0.25 degrees50 deg / 200x
Exit pupil
0.8 mm150 mm / 200x
Max useful mag
about 300x2x aperture
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Skymax 150 the Celestron Omni 9mm Plossl gives 200x with a 0.25 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: 1800 mm divided by 9 mm is 200x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.25 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 150 mm over 200x, 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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Questions and answers

Celestron Omni 9mm Plossl in the Sky-Watcher Skymax 150: magnification and field?

Good fit. In the Sky-Watcher Skymax 150 the Celestron Omni 9mm Plossl gives 200x with a 0.25 degree true field and a 0.8 mm exit pupil, inside the telescope's useful range.