Speaking of binos

[charles m]

Is there any reason that a 30mm lens would be better than a 42mm lens?

Thanks in advance. 

[Bowguy67]

Size, 42 for woods type hunting can be large at times

[Ray Lyon]

Light is better with equal quality glass, however size is also bigger.  If I can’t see it with my 8x30 Swarovski I shouldn’t be on stand anymore

[charles m]

Thanks Ray, but I'm looking for an answer to the question about usage, not about ethics or stand time. 

[Trenton G.]

I hunt fairly thick stuff (cedar swamps, beech slash, etc.) where visibility is oftentimes 50 yards or less, but still don't have any issues with my 10x42. I've found them to be the perfect balance for both close range hunting here and hunting more open country out west.

[Wudstix]

It would depend on the magnification,  6x30 would gather more light than 10x42.
 

[MnFn]

Yup, size.  When I hunted more with a rifle I almost always had my binoculars hanging on my neck. I used a pair of 8x30 Swarovski for years. Then I thought I should have a pair of 10x40 Leicas for hunting out west.

You wouldn’t think it would make that much difference, but it did.  After trying it a few times, I went back to 8x30 and traded off the bigger binos. Literally they were a pain in my neck to carry all day.

[charles m]

Ok Whoa Whoa Whoa!!!

So sorry I didn't clarify.

 8 x 30 and an 8 x42

Is there any reason that a 30mm lens would be better than a 42mm lens?

And which one gathers more light?

Just looking for a TECH answer and not personal preference. Thanks again.

[Ray Lyon]

Let me say it a different way.  I like my binoculars on my chest in my bino harness. They are SMALL enough to stay compactly out of the way, and handy in one hand.  So the SIZE is perfect and it gives me plenty of magnification for my hunting needs (without sacrificing low light needs). Now, if I were hunting sheep or wide open country mule deer and wanted a 10x magnification I would want a 40 or 42 for better light gathering.  But a 30mm exit pupil is plenty for an 8x magnification.  Also, I haven’t priced binoculars for 10 years but I’m guessing there’s a higher cost to larger glass. 

Comment posted after you posted your clarification

[rastaman]

To answer your question Charles, an 8 x 42 gathers more light than an 8 x 30.  For stalking hogs in the thick stuff in south Georgia an 8 x 30 would be better based on size and weight.

[Wudstix]

8x42 gathers more light.  Divide magnification into objective size.  The closer you get to 5 without going over the better.  Has to do with the useable light your eye can take in, I believe the pupil is 5mm, so that is the max.  So, 6x30, 7x35, 8x40, etc....  Then it depends on size/weight of bino around your neck, that tolerance is personal.
 

[Firstlight]

Both will work well, with a little more light, magnification and filed of view with the 8x42.  For me personally, I want the eye pupil, always at least 5mm.  Magnification divided by objective lens.  Anything less is a sacrifice in “light” which is evident in low light situations.

30mm being better?  I guess it depends are how they are being used, what your goal is, and how much light they let in? What environments are you using them in, open areas or dense woods?

I have some great, lightweight binoculars at 7x35 which are fine for hunting but I’m getting a pair of 8x42 soon.  I want a little extra magnification and field of view. I think it comes down how you use them, the physical weight and how you need them to perform in low light. If hunting, given the low light and “shadow” conditions I experience in my area, I start with a 5mm exit pupil so the lenses gather better light.  Vortex viper HD or or diamond back HD, both in 8x42 get some great reviews.  I’m not a “birder”, but that group has done some serious testing on all things binocular related, the information therein lending itself well to the archer.