42mm vs. 50mm Objective

[CiK01]

How much morning or evening time do you gain with the 50mm objective over the 42mm objective? The difference appears to be light transmission in low light......how much time does that equate to? Say you can start effectively glassing with a 42mm binocular at 7am, will a 50mm binocular allow you to start glassing effectively at 6am?

In my research, I always here the 50mm gets you better low light ability. How is that quantified in time?

Tony

 

[5MilesBack]

Say you can start effectively glassing with a 42mm binocular at 7am, will a 50mm binocular allow you to start glassing effectively at 6am?

If you can start glassing at 7am with the 42mm, it will be pitch dark at 6am. We're talking a few minutes here, not an hour. There still has to be some sort of light available.......unless you're using night vision. But those few minutes could be critical to actually spotting animals that are on the move that won't be there a few minutes later.

It also depends on which bino's you're talking about. If you are comparing two of the same bino's, just the difference between their 42 and 50, you'll gain a few minutes. But if you're comparing something like Swaro 42's to a Viper 50.......the Swaro 42's will still be better.

 

[CiK01]

If you can start glassing at 7am with the 42mm, it will be pitch dark at 6am. We're talking a few minutes here, not an hour.

Understood and helpful. I am trying to figure out if that extra length and weight of a 50mm objective vs the 42mm is worth the extra time it allows.

I am not settled on what brand, but I would compare the objective size against the same brand to keep as much consistency as I can.

 

[5MilesBack]

The other thing you need to understand is exit pupil. A 15x56 has an exit pupil of 3.73 (56 divided by 15). A 10x42 has an exit pupil of 4.2. The higher the exit pupil, the more your eyes will be able to use the available light. So you have to look at both the objective size and the power. So if you're comparing the same powers with different objectives that's going to be a fair comparison. So a 10x50 versus a 10x42. But a 12x50 and 10x42 would probably be comparable as far as ability to transfer that light.

The best way to see this in action is with a variable spotting scope. A 20-60x80mm scope has an exit pupil of 1.33 on 60 power, but an EP of 4 on 20 power. In very low light you're going to see a lot better at 20 power than 60 power.

 

[elkguide]

Minutes is what you gain along with weight and size. I have settled on 10X42 Swarovskis and am fine with what time I am able to see what's there. The only extra issue is that if you are rifle hunting, you will also have to step up that glass too in order to make things effective.

 

[GotDraw?]

I know your question asks how many minutes shooting time that larger objectives give you, but I think the way to frame it is to look at it in terms of how much max magnification you plan to need to take a shot at dusk vs. your pupil size. Elkguide posted above that his effective 4.2MM exit pupil works at 10x with his Swaros. If feel you'll need 12x or 15x to take longer shots, then read on... I'm not an eye doc, but my understanding is:

Exit pupil size of your optics is important because on average, the human eye pupil opens to a max average diameter of approx. 5MM when your eye is trying to adapt to darkening environments (varies from person to person). Younger folks perhaps 4-9mm max in total darkness, but the older you are, the smaller your max pupil and this is partially why older folks often don't see as well at night. Therefore, in order to maximize the actual potential amount of light transmitted to your pupil and then your retina, your optics need to gather and deliver as much light as possible. Optics should optimally deliver an exit pupil of light matched to your eye for best dark vision, most folks will be about 5mm. If your variable magnification optics can deliver 5.6 mm of light at 10x (ie 56mm objective divided by 10 power), then most folks should be able to zoom in further until the exit pupil is about 5mm or a little smaller and still be able to see well in a very dark environment. The smaller the exit pupil of your optics, the less light transmitted to your eye and the more the image will degrade.

The above poster, elkguide, uses 10x Swaro binoculars w/42mm objectives, this delivers 4.2mm exit pupil and will work well during most archery hunting/scouting conditions since the eye is not fully dilated because it's not pitch black yet. But, if rifle hunting and wanting 15x magnification to take a longer shot at the darker side of dusk, then a larger 50 to 56mm objective will deliver closer to that exit pupil diameter. The trade off of course is that larger objectives and better glass cost more, weigh more and take more space. You'd better plan for at least a 4mm exit pupil at your magnification requirement in order to be able to shoot at the darker side of dusk.

Unfortunately, "trying out" or "testing" optics in a store is useless. Can you afford to buy two scopes at one time? If so, perhaps you could go to a store w/a good return policy, buy two scopes you're interested in, bring them to a wide open area at dusk, do not mount them, If you can, set up and scope known targets at long range as the sun sets. Compare the scopes and keep the better scope and return the lesser scope, buy another, compare it the next evening to the last winner and keep the new winner. Take notes of the ranges and zooms they worked at and at what distances they were acceptable. Run through this process with several scopes and you will reach an answer that satisfies you rather than trying to determine it from 3rd parties who probably have different eyes and needs than you may. When you're done w/your testing, buy the scope that best intersects your budget vs. needs and return all others.

Best of luck!
JL

 

[camping1601]

Went through this a couple years ago with a Leupold 3.5-10. I decided on the 40mm for weight and all I can say is I can hunt way past legal shooting hours with it. Only benefit of a 50mm to me would be field of view.

Edit- looks like I should have read this better. Missed the part about it being binos. Sorry my bad.

 

[Pontius]

A set of 50mm binos around your neck/on your chest all day gets old quickly. My hunting partner was over it this year - 10x42s next season.

 

[mgebs311]

Great thread! I’m surprised this question did not receive more traction. This is the exact question I have had recently as I’ve been researching binoculars to upgrade to. I currently have 10x50 Vortex Viper HD’s. I am leaning towards 10x42 Swarovski SLC‘s. I really like the idea of a more compact binocular on my chest while hunting, and also having a lot more quality glass that I’m sure will still perform better than my current 10x50’s. I am curious about how many guys using alpha glass feel it is still worth going to a 10x50 over the 10x42? In my case I will most likely choose the 10x42 still instead of the 10x50 because I am looking at the SLC’s and those don’t come in a 10x50. Saving for the EL’s is a pretty far reach for me at this point as I am a poor Fireman lol.

 

[bruceleroy]

If its to dark to see an animal with your 42s then its most likely to dark to shoot at them.