A Tele Vue 8mm Ethos in the Sky-Watcher Heritage 130P gives 81x, a 1.23 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 8mm Ethos in the Sky-Watcher Heritage 130P: magnification and field

What the Tele Vue 8mm Ethos does in the Sky-Watcher Heritage 130P, worked from the published focal lengths and apparent field.

Field of view

ring = 1.23 degrees true
dot = 1.6 mm exit pupil

Computed optics

Magnification
81x650 mm / 8 mm
True field
1.23 degrees100 deg / 81x
Exit pupil
1.6 mm130 mm / 81x
Max useful mag
about 260x2x aperture
Barrel match
1.25 in eyepiece in a 1.25 in focuser
Fits

Good fit. In the Sky-Watcher Heritage 130P the Tele Vue 8mm Ethos gives 81x with a 1.23 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: 650 mm divided by 8 mm is 81x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 1.23 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 130 mm over 81x, which is 1.6 mm. That makes this a medium-power general setting.

The eyepiece to buy

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Related

Sky-Watcher Heritage 130P130 mm f/5
Tele Vue 8mm Ethos8 mm, 100 deg
Best eyepiece for the Sky-Watcher Heritage 130Pexit-pupil match

Questions and answers

Tele Vue 8mm Ethos in the Sky-Watcher Heritage 130P: magnification and field?

Good fit. In the Sky-Watcher Heritage 130P the Tele Vue 8mm Ethos gives 81x with a 1.23 degree true field and a 1.6 mm exit pupil, inside the telescope's useful range.