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On Sun, 16 Feb 2003, Brian Skiff wrote: > (which he admits to). This page contains Roger's threshold vs detection- > probability table from the 1994 S&T article. The 50 percent detection > limit for 10cm (4-inches) aperture is indeed 13.7, as Mike quoted. Its good to see that my figure came quite close to theirs. I started from the flux of Vega (gives mag 0 star of B-V=0 is 3.68e-20 ergs/cm^2/s/hz) and derived the quantum count from it (assuming peak visual at 510nm and BW of 250nm) > Party some years ago. Both the latter indicate reasonable limits of V=8.2 > or so for typical eyes (Nash says his vision is not particularly sharp). Well, I really have doubts about these tests. Personally, I cant seem to do much better than about 6.8 from Mauna Kea, and I think my sensitivity is pretty good even though my acuity is about 20/30, which is probably the limiting factor. But, I can estimate down to about 16.3 with my 37cm under ideal conditions, since I can then focus precisely, which is right at my 50% threshold as I calculated, so I feel pretty good about this. Most observers I personally met are about that same level. It seems to me some kind of bias is going on in selecting particularly sensitive individuals for these tests, or they are not being 100% honest? > instead physio- and psychological factors weigh heavily. Basically, the > experienced old observers with 4-5mm pupils see just as faint as younger > folks with 7-8mm pupils. And of course telescopically pupil size doesn't This seems odd. One of the key factors in naked eye, and it is in the formula I used to derive it as well, is the aperture of the eye. The difference between 4.5mm and 7.5mm is 1.1 magnitudes. But there may be some compensatory effect going on with the older eyes, that is as the pupil size decreases slowly, the retina develops a lower throshold of signal detection? Dont know if anyone has studied this in detail. Mike Linnolt
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