Date: 3/20/17 5:06 pm
From: Warblerick <ricksussman1955...>
Subject: Re: [MDBirding] Re: Binoculars, Good selection of 12x
12x25? Wow, I've never heard of anyone using that for birding. The image can't be very bright. The exit pupil on 12x25's is about 2mm, or roughly half what your open pupil is (4-5 mm for most adults in regular light). So you're only getting about half the available light. Most recommended birding binoculars have numbers like 7x35 or 8x40, with an exit pupil of 5, which just about matches your own pupil, allowing all the light coming through the eyepiece to be used, giving a nice bright image. 12x25 must be like looking through a keyhole, I would think.

Rick Sussman
Woodbine, MD

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