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Message: <blockquote data-quote="WJC" data-source="post: 3151599" data-attributes="member: 25191">:cat:Apologies to all:I tried hard to stay away from this thread; I just wasn’t man enough. Sorry!As most folks in astronomy and telescope making know, “A longer focal ratio can hide a multitude of sins,” and, whether we like it or not, our eyes (with all their faults*), are part of our binocular system.In low light, the average eye is working at about f/4. That is, in the vernacular of UAs Optical Sciences Center, “bad Ju Ju.” When our pupils are stopped down in bright daylight, they may reach f/11 or . . . “good Ju Ju.”A wide-angle has little to do with brightness. For more optical scripture: “The objective giveth, and the eyepiece taketh away.”The larger the objective, the more light can enter the instrument, and the brighter the image can be at a given opening for our biological pupils. Because, as magnification increases image brightness decreases, a bino with a bright, crisp image at 7-8 power, will be dimmer and somewhat fuzzier at 16-20 power, although the binoculars have exactly the same clear aperture. The attached photo illustrates how this works. At a distance of 1 foot, a light source has a brightness of X, but when the distance is only doubled, the brightness is only ¼ X. Thus, it is easy to see how you can quickly get into “diminishing returns,” without even considering any number of mechanical considerations.Bill* This is one of the reasons why trying to compare two binos with the same aperture, magnification, and nearly the same quality is senseless—it’s kinda like trying to ice skate UPHILL! There are just TOO MANY VARIABLES. And although much has been written about the differences in coatings, it’s just not so—observably so, anyway.Sure there are differences. But trying to evaluate coatings for companies of similar experience in optics, is like trying to split hairs with an axe. Baffling, blackening, absorption of light by the glass in the elements, size and position of the field stop, knife-edge on the field stop, and other considerations take a toll. It’s like the 5th engine on a 747 (the APU). Just because most people are not familiar with it doesn’t mean it doesn’t exist.</blockquote>

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