Quote:
Originally Posted by Robh
This is not too say you can't have a longer focal length eyepiece but the extra light it sends to your eye will be wasted. Of course, if you have a night-time pupil size of 7mm, you can use focal ratio x7.
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And further on this point, just because you will loose light due to a too large exit pupil, it doesn't mean that you can't get a splendid view from an eyepiece outside the normal range.
Peter Brooks did a nice spreadsheet of eyepieces, and I modified it to include the use of a paracor. I can't add it here, so I will upload it to the SDM Telescopes website shortly and post a link.