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29 Nov

Binocular light transmission percentages

Posted by Joannie K on

Customers frequently ask the light transmission percentage on various models of binoculars, since this is a spec rarely specified by the manufacturers. I suspect there are several reasons for light transmission percentages not often being posted as a spec for a binoculars. One, there is no standardized way of measuring light transmission, so even if posted, it means relatively little unless it is the result of a test where there was a direct comparison with other models. However, the percentage means little outside of this test since no one has devised a test that is universally used by all manufacturers. Another reason, I suspect, is that numbers can be misleading and often suggest a significance they do not have. For instance, I read somewhere that the human eye cannot detect differences in light smaller than 3%. That suggests that a difference between a binocular with a 94% light transmission and one with a 96% transmission means very little, if anything. Lastly, no one test can duplicate the actual conditions where a binocular will be used. May not be very scientific, but I have seen wide variations in image brightness performance for a specific model of binocular under the lights of a store, out in the field at dusk and, finally, under conditions of full darkness. Awfully hard to predict this aspect of binocular performance until you get the binocular out and test it for a specific situation and, again, the only real test is a side by side comparison. Specs like exit pupil, lens coatings and even light transmission, when posted, can only take you so far.

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