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What possible harm would there be to anyone in having the manufacturers report the RFOV? Why does Baader feel it is important to report the RFOV? It is a simple, practical, and quite useful tool.

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And as the original poster ascertained, AFOV's do not tell anyone what they will actually see, but rather only how far the eye will have to glance from side to side to see the REAL field that the eyepiece and telescope are presenting to the viewer. In his actual example, as regards the true field that he expected to see based on the apparent field, the AFOV was off by 12.7% in one direction for one eyepiece, and 4.9% in the other direction for another eyepiece, for a combined error of 17.6% in his simple yet futile attempt to use AFOV's to compare one eyepiece against another. With RFOV this error would be reduced to near zero.

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Ah, not quite. He didn't get the true field expected because he used the approximation TFOV = AFOV/Mag and did not understand that it *is* an approximation. Had he used the field stop method, he would have been considerably closer to reality. As for apparent field, it shows the angular width that the eye sees when looking into the eyepiece (from field stop edge to field stop edge usually). Thus, it *does* show what the observer will see, not in terms of true field of view, but in the width of what is presented to the eye. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org

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