A Tele Vue 13mm Ethos in the Sky-Watcher Skymax 127 gives 118x, a 0.84 degree true field and a 1.1 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 Skymax 127: magnification and field

What the Tele Vue 13mm Ethos does in the Sky-Watcher Skymax 127, worked from the published focal lengths and apparent field.

Field of view

ring = 0.84 degrees true
dot = 1.1 mm exit pupil

Computed optics

Magnification
118x1540 mm / 13 mm
True field
0.84 degrees100 deg / 118x
Exit pupil
1.1 mm127 mm / 118x
Max useful mag
about 254x2x aperture
Barrel match
2 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Skymax 127 the Tele Vue 13mm Ethos gives 118x with a 0.84 degree true field and a 1.1 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1540 mm divided by 13 mm is 118x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 0.84 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 127 mm over 118x, which is 1.1 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

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Related

Sky-Watcher Skymax 127127 mm f/12.1
Tele Vue 13mm Ethos13 mm, 100 deg
Best eyepiece for the Sky-Watcher Skymax 127exit-pupil match

Questions and answers

Tele Vue 13mm Ethos in the Sky-Watcher Skymax 127: magnification and field?

Good fit. In the Sky-Watcher Skymax 127 the Tele Vue 13mm Ethos gives 118x with a 0.84 degree true field and a 1.1 mm exit pupil, inside the telescope's useful range.