Q: I’m in the market for a binocular and have just about decided on a 10×25, which is light and handy and will fit in the pocket of my jacket.Â
Most of my hunting is in mountain country for goats and deer and I’m glassing across wide gullies and open mountainsides.Â
What do you think of my choice?
Roley Dean
A: I don’t think much of your choice! A basic optical principle is that the higher the magnification, the larger in diameter the objective lenses should be, both to allow sufficient light to reach your eyes and for optical sharpness (resolution).
While some pocket binoculars are well-made, objective lenses 20 to 28mm in diameter simply can’t provide the brightest, sharpest view.
A 10-power glass normally requires at least a 40mm objective, adding to the cost and size. Some hunters find a full-size 10×40 a little clumsy for all-round use, but dropping to 8x allows a smaller diameter objective and overall size and weight.
An 8×32 has as large an exit pupil as a 10×40 and plenty of magnification for most hunting. So instead of a handy but inadequate 10×25, or a more bulky, not so handy 10×40, you’d be better off with an 8×32.
Having said that, my hunting glass is a 10×42 Leica, but my mates show a preference for the 8×42.
Bear in mind that for a 4mm exit pupil you need a 28mm objective in a 7x binocular, 32mm in an 8x and 40mm in a 10x.
Anything smaller and viewing in anything but bright sunlight will be disappointing.
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