Choosing the right size binoculars

Size counts: Choosing the best binoculars

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. 

Most of my hunting is in mountain country for goats and deer and I’m glassing across wide gullies and open mountainsides. 

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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Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.