Eyepiece and telescope pairing
Tele Vue 3.5mm Delos in the Celestron NexStar Evolution 9.25: magnification and field
What the Tele Vue 3.5mm Delos does in the Celestron NexStar Evolution 9.25, worked from the published focal lengths and apparent field.
Field of view
ring = 0.11 degrees true
dot = 0.3 mm exit pupil
- Magnification
- 671x2350 mm / 3.5 mm
- True field
- 0.11 degrees72 deg / 671x
- Exit pupil
- 0.3 mm235 mm / 671x
- Max useful mag
- 555xpublished
Computed optics
- Barrel match
- 1.25 in eyepiece in a 2 in focuser
Over-powered. At 671x this pair exceeds the published highest useful magnification of about 555x for the Celestron NexStar Evolution 9.25, 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: 2350 mm divided by 3.5 mm is 671x. The true field of view is the eyepiece's 72 degree apparent field divided by that magnification, 0.11 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 235 mm over 671x, 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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