A Tele Vue 40mm Plossl in the Sky-Watcher Skymax 180 gives 68x, a 0.74 degree true field and a 2.7 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Tele Vue 40mm Plossl in the Sky-Watcher Skymax 180: magnification and field

What the Tele Vue 40mm Plossl does in the Sky-Watcher Skymax 180, worked from the published focal lengths and apparent field.

Field of view

ring = 0.74 degrees true
dot = 2.7 mm exit pupil

Computed optics

Magnification
68x2700 mm / 40 mm
True field
0.74 degrees50 deg / 68x
Exit pupil
2.7 mm180 mm / 68x
Max useful mag
about 360x2x aperture
Barrel match
2 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Skymax 180 the Tele Vue 40mm Plossl gives 68x with a 0.74 degree true field and a 2.7 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 2700 mm divided by 40 mm is 68x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 0.74 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 180 mm over 68x, which is 2.7 mm. That makes this a medium-power general setting.

The eyepiece to buy

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Questions and answers

Tele Vue 40mm Plossl in the Sky-Watcher Skymax 180: magnification and field?

Good fit. In the Sky-Watcher Skymax 180 the Tele Vue 40mm Plossl gives 68x with a 0.74 degree true field and a 2.7 mm exit pupil, inside the telescope's useful range.