A Tele Vue 8mm Ethos in the Sky-Watcher Classic 200P (8-inch Dobsonian) gives 150x, a 0.67 degree true field and a 1.4 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 Classic 200P (8-inch Dobsonian): magnification and field

What the Tele Vue 8mm Ethos does in the Sky-Watcher Classic 200P (8-inch Dobsonian), worked from the published focal lengths and apparent field.

Field of view

ring = 0.67 degrees true
dot = 1.4 mm exit pupil

Computed optics

Magnification
150x1200 mm / 8 mm
True field
0.67 degrees100 deg / 150x
Exit pupil
1.4 mm203 mm / 150x
Max useful mag
about 406x2x aperture
Barrel match
1.25 in eyepiece in a 2 in focuser
Fits

Good fit. In the Sky-Watcher Classic 200P (8-inch Dobsonian) the Tele Vue 8mm Ethos gives 150x with a 0.67 degree true field and a 1.4 mm exit pupil, inside the telescope's useful range.

Magnification is the telescope focal length divided by the eyepiece focal length: 1200 mm divided by 8 mm is 150x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 0.67 degrees.

The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 203 mm over 150x, which is 1.4 mm. That makes this a high-power lunar, planetary and double-star setting.

The eyepiece to buy

Shop Tele Vue 8mm Ethos on AmazonaffiliateFind Tele Vue 8mm Ethos on eBayaffiliate

Related

Sky-Watcher Classic 200P (8-inch Dobsonian)203 mm f/5.9
Tele Vue 8mm Ethos8 mm, 100 deg
Best eyepiece for the Sky-Watcher Classic 200P (8-inch Dobsonian)exit-pupil match

Questions and answers

Tele Vue 8mm Ethos in the Sky-Watcher Classic 200P (8-inch Dobsonian): magnification and field?

Good fit. In the Sky-Watcher Classic 200P (8-inch Dobsonian) the Tele Vue 8mm Ethos gives 150x with a 0.67 degree true field and a 1.4 mm exit pupil, inside the telescope's useful range.