Proving power question.

[jpsmith1]

I bought a cheap pair of 8x binos at Wal-mart for dashboard use.  They will ride around a lot and be used a little.  Anyway, I used them this evening to check out a small herd of deer in a field at about 200-300 yards.  It was a little dark, but it still didn't seem like they provided the 8x as advertised.  My Nikon 10x50s give a much better image, of course, but more importantly, seem to provide a heck of a lot more magnification.

Basically, is there any way to 'prove' the power of a optics?  Would comparing them to a riflescope set on 8x be a valid comparison?

[Dave in WV]

To Prove the power question you really need to compare optics of equal quality. $50 10x50 vs. $300 8x42 or vice versa doesn't really prove a thing. Greater magnification (with an exit pupil to equal at leat 4mm) does help IF the optics are of equal quality.

[Graybeard]

Exactly. Once many years ago when I was building binoculars for a living I made a pair for myself. I used only the best B&L glass and matched it all up perfectly. The binocular was only a 6x30 but to me that's one of the most useful glasses there is for woods hunting such as I do.

Way back in those days some 35+ years ago I still went to a few local high school football games. One night I was sitting next to a lady who's kid was in the band and she really wanted to be able to watch them up close and personal at half time. The cheap 7x35s she had were really pathetic and she wasn't seeing the kid very clearly. I handed her mine to use during half time. Her immediate comment to me was wow your binoculars are so much more powerful than mine. Not really as hers were 7X compared to mine at 6X. I got that same comment from others with cheap binos up to 8X and even 10X.

It's NOT really the magnification nearly so much as the optical quality of the glass that makes the difference in what you see and that fools the eyes into thinking one is more powerful than the other when all you're really experiencing is a clear bright image vs. a dim fuzzy one.

[jpsmith1]

I suppose that that's why they looked a whole lot better under the bright light of day this morning.  I compared them side by side at maybe 30 yards today.  The images were comparable as far as magnification was concerned.  Theres no way that the cheap  8x21s can compare to my Nikon 10x50s for brightness.  Oh well, you get what you pay for, I guess.

[Dave in WV]

8x21 binoculars can't compete with 10x50 binoculars even if of same quality. I'd rather have $350 10x50s than $1000 8x21s. When you have less than a 4mm exit pupil the light transmission and clarity are inferior. The 8x21 has an exit pupil of 2.6mm and the 10x50 5mm. No contest.

[jpsmith1]

I knew that they'd never compare quality wise to my Nikons, but I needed a pair of binoculars to get knocked around and still be able to show me something at some range.  Size was also a consideration, something that fits in a cupholder is great.  It appears that an upgrade is already in order, though.

[Graybeard]

It appears that an upgrade is already in order, though.

It ALWAYS is when you start out really cheap. Optics is one place that dirt cheap has no place in my mind. You can get by with cheaper rifle scopes than you can binoculars or spotting scopes in my experience. Those are the last two places to scrimp on the budget.