Eyepiece and telescope pairing
Tele Vue 6mm Ethos in the Sky-Watcher Skymax 180: magnification and field
What the Tele Vue 6mm Ethos does in the Sky-Watcher Skymax 180, worked from the published focal lengths and apparent field.
Field of view
ring = 0.22 degrees true
dot = 0.4 mm exit pupil
- Magnification
- 450x2700 mm / 6 mm
- True field
- 0.22 degrees100 deg / 450x
- Exit pupil
- 0.4 mm180 mm / 450x
- Max useful mag
- about 360x2x aperture
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Over-powered. At 450x this pair exceeds the highest useful magnification of about 360x for the Sky-Watcher Skymax 180, 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: 2700 mm divided by 6 mm is 450x. The true field of view is the eyepiece's 100 degree apparent field divided by that magnification, 0.22 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 180 mm over 450x, which is 0.4 mm. That makes this a high-power lunar, planetary and double-star setting.
The eyepiece to buy
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