A Tele Vue 13mm Ethos in the Sky-Watcher Evostar 80ED gives 46x, a 2.17 degree true field and a 1.7 mm exit pupil. The worked calculation and whether it sits in the useful range.

Updated 05 September 2026.

Eyepiece and telescope pairing

Tele Vue 13mm Ethos in the Sky-Watcher Evostar 80ED: magnification and field

What the Tele Vue 13mm Ethos does in the Sky-Watcher Evostar 80ED, worked from the published focal lengths and apparent field.

Field of view

ring = 2.17 degrees true
dot = 1.7 mm exit pupil

Computed optics

Magnification
46x600 mm / 13 mm
True field
2.17 degrees100 deg / 46x
Exit pupil
1.7 mm80 mm / 46x
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 13mm Ethos gives 46x with a 2.17 degree true field and a 1.7 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 13 mm is 46x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 2.17 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 80 mm over 46x, which is 1.7 mm. That makes this a medium-power general setting.

The eyepiece to buy

Shop Tele Vue 13mm Ethos on AmazonaffiliateFind Tele Vue 13mm Ethos on eBayaffiliate

Related

Sky-Watcher Evostar 80ED80 mm f/7.5
Tele Vue 13mm Ethos13 mm, 100 deg
Best eyepiece for the Sky-Watcher Evostar 80EDexit-pupil match

Questions and answers

Tele Vue 13mm Ethos in the Sky-Watcher Evostar 80ED: magnification and field?

Good fit. In the Sky-Watcher Evostar 80ED the Tele Vue 13mm Ethos gives 46x with a 2.17 degree true field and a 1.7 mm exit pupil, inside the telescope's useful range.