A Tele Vue 20mm Plossl in the Sky-Watcher Skymax 102 gives 65x, a 0.77 degree true field and a 1.6 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Tele Vue 20mm Plossl in the Sky-Watcher Skymax 102: magnification and field

What the Tele Vue 20mm Plossl does in the Sky-Watcher Skymax 102, worked from the published focal lengths and apparent field.

Field of view

ring = 0.77 degrees true
dot = 1.6 mm exit pupil

Computed optics

Magnification
65x1300 mm / 20 mm
True field
0.77 degrees50 deg / 65x
Exit pupil
1.6 mm102 mm / 65x
Max useful mag
about 204x2x aperture
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Skymax 102 the Tele Vue 20mm Plossl gives 65x with a 0.77 degree true field and a 1.6 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1300 mm divided by 20 mm is 65x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.77 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 102 mm over 65x, which is 1.6 mm. That makes this a medium-power general setting.

The eyepiece to buy

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Related

Sky-Watcher Skymax 102102 mm f/12.7
Tele Vue 20mm Plossl20 mm, 50 deg
Best eyepiece for the Sky-Watcher Skymax 102exit-pupil match

Questions and answers

Tele Vue 20mm Plossl in the Sky-Watcher Skymax 102: magnification and field?

Good fit. In the Sky-Watcher Skymax 102 the Tele Vue 20mm Plossl gives 65x with a 0.77 degree true field and a 1.6 mm exit pupil, inside the telescope's useful range.