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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12785
Loc: Cumberland, R I , USA42N71.4W
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Re: Advantages of 10x50 over 8x42?
07/08/08 06:57 AM
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Well, about 10 years ago Alan Adler did some preliminary studies that showed Roy Bishop's Index (the index you refer to above) does not really give an accurate indication of how binoculars perform on stars. In fact, he claimed a better index would be magnification times square root of aperture.
So, about 6-7 years ago, I spent months of exhaustive testing and found that Alder is on the right track. Diameter of aperture is fairly meaningless for binocular performance and over-weights performance to aperture. And if you think about it a little further, there are no circumstances where diameter of aperture is a significant value for binocular viewing. Area of aperture is better. But finally, aperture has far less influence on binocular performance than magnification. So magnification needs to be weighted.
By both Adler's Index and my BPI, an equal quality 10x50 vs an 8x42 would give about a 35% increased performance, not nearly the 56% increae that would be predicted by Bishop's Index. You can find previous discussions in this forum that show smaller aperture binoculars with higher power perform at an advantage to larger binoculars at a lower power.
Of course the reason behind this is the fact that for most targets the optimum use of all the aperture is so drastically under-utilized at low powers that you never get the full benefit of the full aperture. But you do get an immediate and full benefit from added magnification. The tests that show this are repeatable and consistent.
See the "Best Of" thread for all the historical discussions in this forum regards Binocular Performance Index.
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