Eyepiece and telescope pairing
Explore Scientific 18mm 82 Degree in the Celestron C5 optical tube: magnification and field
What the Explore Scientific 18mm 82 Degree does in the Celestron C5 optical tube, worked from the published focal lengths and apparent field.
Field of view
ring = 1.18 degrees true
dot = 1.8 mm exit pupil
- Magnification
- 69x1250 mm / 18 mm
- True field
- 1.18 degrees82 deg / 69x
- Exit pupil
- 1.8 mm127 mm / 69x
- Max useful mag
- 295xpublished
Computed optics
- Barrel match
- 1.25 in eyepiece in a 1.25 in focuser
Good fit. In the Celestron C5 optical tube the Explore Scientific 18mm 82 Degree gives 69x with a 1.18 degree true field and a 1.8 mm exit pupil, inside the telescope's useful range.
Magnification is the telescope focal length divided by the eyepiece focal length: 1250 mm divided by 18 mm is 69x. The true field of view is the eyepiece's 82 degree apparent field divided by that magnification, 1.18 degrees.
The exit pupil, the width of the light beam leaving the eyepiece, is the aperture divided by the magnification, 127 mm over 69x, which is 1.8 mm. That makes this a medium-power general setting.
The eyepiece to buy
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