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Old 23-02-2018, 01:57 PM
AstroStudentUSQ (Mark)
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Join Date: Sep 2017
Location: Adelaide
Posts: 63
Excellent points and very useful info re-equation, thank you Don!

Cheers,
Mark


Quote:
Originally Posted by Don Pensack View Post
80° requires a minimum of 33.6mm of eye lens diameter for 20mm of eye relief
30mm of eye lens diameter and 20mm of eye relief means a maximum of 73.7° apparent field.
If these eyepieces do indeed have an apparent field of 80° then the eye relief is really 17.9mm. That's still pretty long for an 80° eyepiece.

If you want to work the math for yourself:
tan0.5ApparentField = 0.5lens diameter / eye relief

One adjustment to that: the depth of the concavity of the eye lens is added to the eye relief so calculated. If the LHD has an eye lens that is 1mm concave, then eye relief could be 18.9mm.
If the eye lens is convex, the convexity amount is subtracted from the calculated eye relief.
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