A Tele Vue 40mm Plossl in the Sky-Watcher Evostar 80ED gives 15x, a 3.33 degree true field and a 5.3 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 Evostar 80ED: magnification and field

What the Tele Vue 40mm Plossl does in the Sky-Watcher Evostar 80ED, worked from the published focal lengths and apparent field.

Field of view

ring = 3.33 degrees true
dot = 5.3 mm exit pupil

Computed optics

Magnification
15x600 mm / 40 mm
True field
3.33 degrees50 deg / 15x
Exit pupil
5.3 mm80 mm / 15x
Max useful mag
189xpublished
Barrel match
2 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Evostar 80ED the Tele Vue 40mm Plossl gives 15x with a 3.33 degree true field and a 5.3 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 40 mm is 15x. The true field of view is the eyepiece's 50 degree apparent field divided by that magnification, 3.33 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 80 mm over 15x, which is 5.3 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
Tele Vue 40mm Plossl40 mm, 50 deg
Best eyepiece for the Sky-Watcher Evostar 80EDexit-pupil match

Questions and answers

Tele Vue 40mm Plossl in the Sky-Watcher Evostar 80ED: magnification and field?

Good fit. In the Sky-Watcher Evostar 80ED the Tele Vue 40mm Plossl gives 15x with a 3.33 degree true field and a 5.3 mm exit pupil, inside the telescope's useful range.