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Here are calculated "RFOVs" for the various Nagler eyepieces: 77.6, 77.1, 81.0, 78.5, 81.9, 79.1, 77.6, 81.6, 77.6, 78.9, 79.4, 80.2, 78.6, 77.9. How are these numbers easier to use in the field or elsewhere than the effective field stop diameters that Tele Vue quotes?

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They do have a significant advantage in that they speak directly to the observer, and they are directly valid and true in the equation:

TFOV = RFOV/Mag

The simplicity and intuitiveness of this trumps calculations and comparisons involving field stop numbers. Mike, you and I are in professions where complex calculations are a daily happening. Most others are not. We must attempt to see the world though their glasses.

Back to how the RFOV speaks to the observer directly and intuitively. I offer an example using the findings of the first poster to this thread. He observed that the RFOV of the 68 degree AFOV Hyperion and the RFOV of the 82 degree Nagler were virtually one and the same. He thereby intuitively knows that despite the markings on the eyepieces, they will in fact show him the exact same amount of the night sky, assuming only that their FL's are the same. Is this not immediately intuitive and simple?

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My philosophy, in essence, is the concept of man as a moral being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute.

Ayn Rand (in the appendix to 'Atlas Shrugged')

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