Eyepiece and telescope pairing
Tele Vue 4.5mm Delos in the Sky-Watcher Skymax 102: magnification and field
What the Tele Vue 4.5mm Delos does in the Sky-Watcher Skymax 102, worked from the published focal lengths and apparent field.
Field of view
ring = 0.25 degrees true
dot = 0.4 mm exit pupil
- Magnification
- 289x1300 mm / 4.5 mm
- True field
- 0.25 degrees72 deg / 289x
- Exit pupil
- 0.4 mm102 mm / 289x
- Max useful mag
- about 204x2x aperture
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Over-powered. At 289x this pair exceeds the highest useful magnification of about 204x for the Sky-Watcher Skymax 102, 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: 1300 mm divided by 4.5 mm is 289x. The true field of view is the eyepiece's 72 degree apparent field divided by that magnification, 0.25 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 102 mm over 289x, 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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