One of the best articles I’ve ever read concerning the calculation of “everything” involving telescope eyepieces….as following:

https://skyandtelescope.org/astronomy-equipment/choosing-your-telescopes-magnification/

I was fortunate to meet Al Nagler a few years ago at the Southern Star Astronomy Convention in Little Switzerland, North Carolina.

Al gave a great presentation concerning eyepiece designs and calculations, based in-part on the above link.

The story:

There was a cancellation by a scheduled Southern Star participant, the last minute. I knew Sue French and Alan were at NEAF. So I called Sue via telephone, asking if Al Nagler was there, and if so would he be interested in giving a presentation for the convention.

Sue called back and said Al was “indeed” interested. I got things worked out with the Charlotte Amateurs and plane tickets for both Al and his wife…and the rest is history.