Eyepiece and telescope pairing
Tele Vue 2.5mm Nagler Type 6 in the Sky-Watcher Evostar 100ED: magnification and field
What the Tele Vue 2.5mm Nagler Type 6 does in the Sky-Watcher Evostar 100ED, worked from the published focal lengths and apparent field.
Field of view
ring = 0.23 degrees true
dot = 0.3 mm exit pupil
- Magnification
- 360x900 mm / 2.5 mm
- True field
- 0.23 degrees82 deg / 360x
- Exit pupil
- 0.3 mm100 mm / 360x
- Max useful mag
- 236xpublished
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Over-powered. At 360x this pair exceeds the published highest useful magnification of about 236x for the Sky-Watcher Evostar 100ED, so the image dims and softens without showing more real detail. Use a longer eyepiece.
Magnification is the telescope focal length divided by the eyepiece focal length: 900 mm divided by 2.5 mm is 360x. The true field of view is the eyepiece's 82 degree apparent field divided by that magnification, 0.23 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 100 mm over 360x, which is 0.3 mm. That makes this a high-power lunar, planetary and double-star setting.
The eyepiece to buy
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