Eyepiece and telescope pairing
Explore Scientific 30mm 82 Degree in the Celestron C9.25 optical tube: magnification and field
What the Explore Scientific 30mm 82 Degree does in the Celestron C9.25 optical tube, worked from the published focal lengths and apparent field.
Field of view
ring = 1.05 degrees true
dot = 3 mm exit pupil
- Magnification
- 78x2350 mm / 30 mm
- True field
- 1.05 degrees82 deg / 78x
- Exit pupil
- 3 mm235 mm / 78x
- Max useful mag
- 555xpublished
Computed optics
- Barrel match
- 2 in eyepiece in a 2 in focuser
Good fit. In the Celestron C9.25 optical tube the Explore Scientific 30mm 82 Degree gives 78x with a 1.05 degree true field and a 3 mm exit pupil, inside the telescope's useful range.
Magnification is the telescope focal length divided by the eyepiece focal length: 2350 mm divided by 30 mm is 78x. The true field of view is the eyepiece's 82 degree apparent field divided by that magnification, 1.05 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 235 mm over 78x, which is 3 mm. That makes this a medium-power general setting.
The eyepiece to buy
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