Objective Lens: How Large is Large Enough?

[Thirteenth Star]

I recently purchased an 8x42 pair of binoculars. This is the first large pair of binocs I've purchased and I'm very happy with the image clarity, particularly at night. It seems as though so little light is lost traveling through the binoculars, that objects viewed with my naked eyes appear just as bright as they are when viewing them through the binoculars.

These binoculars have objective lenses of 42mm, at a magnification of 8x, which gives us an exit pupil of 5.25mm. There are binoculars, though, with exit pupils as wide as 7mm. However, images viewed through the binoculars can't appear brighter than the imges are perceived without the binoculars, since that would imply the creation of light. So then, what is the purpose of binoculars with large enough objective lenses and low enough magnifications to yield an exit pupil width as high as 7mm?

 

[maximus otter]

If you are under 30 years of age, your pupils can dilate to 6mm or even more. This is where exit pupils of >5mm come into their own. I own and enjoy a pair of Zeiss (East) 7 x 50mm. I just can't exploit their abilities to the full.

If, like me, 30 is a distant memory ( ), 5.25mm is just fine.

maximus otter

 

[faramir]

As MO said is presumeably the maximum for majority of the population, hence new 8x56 (7 mm exit pupil diameter) sizes. Your binoculars should be just fine and the quality of the glass and coatings can quickly outweigh the additional aperture. Note that binoculars manufacturers specify light transmission of their elements ranging from as low as 75% to as high as 99+% - so technically 10% loss due to smaller aperture, even if your eye pupil could dillate that far, can be more than compensated by decent optics and materials.

BTW, I've got 8x50 binoculars and they work like a charm too

 

[mete]

Yes , lense coatings make all the difference in the world. The best have 4 coatings. It's very important to clean the lenses properly because if you wear away or scratch the coatings you have ruined the binoculars.

 

[Cougar Allen]

However, images viewed through the binoculars can't appear brighter than the imges are perceived without the binoculars, since that would imply the creation of light.

There's some confusion here.... No new light is created, but the light gathered by an objective lens that's larger than the pupil of your eye is focused down. That's why binoculars give a brighter view than the naked eye.

 

[faramir]

Oh and one more thing regarding "brighter" image: percieved color (saturation and tint) depend on type of glass used in lenses and prisms and oncoatings used - some binoculars are known for their "brighter" tone (slightly yellowish tint to picture) which makes the foggy/cloudy northern weather look less lousy Some binoculars offer more neutral representation but that's usually not what people want (the image looks "too dark"). Differences are noticable even among product families of same manufacturer. Most people want this "brighter" image, as long as the yellow tint isn't too obvious.

 

[LFH]

My hunting glasses are 16x50. Wife's are 12x50. The 50 gives me a lot more light input for early morning and late evening. The 16x gives me great magnification to better identify all the characteristics of an animal as to whether I want to shoot it or not.

Wife likes the 12x magnification. A little lighter for her to hold.

Easy enough to compare different ones at the large sporting goods places before you buy.

I would never recommend anything less than 10x50. Used too many of the smaller ones and they just don't do it for me.

 

[faramir]

LFH, do you use those 16x for short period of time only or do you have incredibly steady hands ? The shaking that becomes more and more obvious with 10+ magnification is partially compensated by the brain but this causes severe strain (and consequently headache) to most of us You're the first person that I ever met who prefers 16x without tripod

 

[maximus otter]

I would never recommend anything less than 10x50.

"Higher magnifications generally limit both the field of view and the depth of field of binoculars. Worse, however, is magnification's affect on image steadiness. As you increase the magnification you are also magnifying every motion of the binoculars. It is next to impossible to extract information from an image that is bouncing around."

"...in objective tests conducted by Zeiss, birders consistently extracted the most detail...from a 7 power image."

"...my general recommendation, after years of testing and using binoculars, is that 8X is just about the ideal power for birding...enough power to give a satisfyingly large image of the bird, but not enough to cause undue fatigue."

http://betterviewdesired.com/BirdW.html

maximus otter

 

[Temper]

Another thing too is what you pay for them which basically means how good the glass is. Last year when I thought I was going to land a job that would have allowed me to treat myself to a $1000 pair of binoculars I asked here and was forced ) )to look at the Swarovski. The x42 models absolutely blew everything else out of the water, well, perhaps not the Leica and Zeiss but certainly anything $800 or less. I looked through a pair of 10 x 50 Nikons that were around $400 and just handed them back a second after putting them to my eyes. There is just no comparison in clarity.

 

[Thirteenth Star]

I now understand what happened.

My pupils are capable of opening to an aperature wider than 5.25mm. However, my eyes were not fully night adapted, hence it seemed as though no light was lost at an exit pupil of 5.25mm. However, had I allowed my pupils to fully open, I'd notice light loss through the binoculars.

 

[Thirteenth Star]

One more thing...

When I was a little younger and a little less knowledgable, I purchased a pair of 9-27X25 binocs. Zoomed to 27x, the exit pupil is about .93mm.

 

[PWork]

7X or 8X and 35mm - 50mm objectives will give you the best overall performance.

Paul

 

[=Voodoo=]

8 X 50 steiners get issued to us in the Army. I have no complaints with them.

 

[faramir]

One more thing...

When I was a little younger and a little less knowledgable, I purchased a pair of 9-27X25 binocs. Zoomed to 27x, the exit pupil is about .93mm.

"Zoom" binoculars have even more downsides (other than ridiculously low aperture at higher magnification):

- it's hard to hold them steady at higher mag., giving you headache
- their field of view is very limited
- introduction of zooming mechanics is yet another place where binoculars could be knocked out of alignment (collimation issues)

Bottom line is: if you ever think you need zoom binoculars just have a look through them and think again Buy a scope and tripod for huge magnification and regular binoculars for carry.

Temper: Swarovski, Zeiss and Leica are dubbed "the big three" for a reason $1000 won't get you Swarovski binoculars anymore though (larger pieces from either SLC or EL line), it appears that they are currently the most expensive binoculars around (not even on par with Leica and Zeiss anymore)

 

[LFH]

Faramir

LFH, do you use those 16x for short period of time only or do you have incredibly steady hands ? The shaking that becomes more and more obvious with 10+ magnification is partially compensated by the brain but this causes severe strain (and consequently headache) to most of us You're the first person that I ever met who prefers 16x without tripod

I use them for my hunting (deer,turkey) Probably don't hold them to my eyes for more than 5 minutes at a time, usually. But have watched yearling deer out at 300 yards playing for 30 or more minutes. No, doesn't cause me headaches.

I don't notice shake or fatigue. I used to use 10x but enjoy the higher magnification of the 16x. If I am selecting a nice buck deer, I like to completely scope his antlers before making a decision to shoot. Can't do that out at 200 yards with 7 or 8x .

So I guess I would only be using them mostly for short time intervals. Yes, at closer distances the 7 or 8x by 50 would suffice. Those just don't work for me. I haven't used anything under 10x by 50 for the last 25 years.

as a funny,,,we have a cabin on a river where thousands of people float by on innertubes, rafts, canoes. Is also in an area with lot of different birds. One that is becoming less rare is a double tipped redbreast.

Yeah,, you guessed it, A topless girl with a sunburn! NOW, tell me, what glasses are you going to pick up the 7x35's or the 10 or 12X50's. There always seems to be a fight over the 10 and 12x ones that we have there. Finally sold the 7x35's in a garage sale.

Like I said an earlier post. Ya just have to go to one of the big sporting goods places and try them all and decide for your self.

 

[Thirteenth Star]

Does anybody know why a 42mm front lens is a common specification for 8x binocs? Why do I not see 8x40mm or 8x45mm binocs often, if at all?

 

[faramir]

Well, it's 2 extra mlimeters and consequently 0.25 mm wider pupil, what's not to like there ? It's not that "common" anyway IMHO, no more common than many other dimensions. I've seen objective diameters ranging from 30 to 56 in 8x regular (= not compact) binoculars; 30, 32, 40, 42, etc., depending on manufacurer and what's currently "chic".

One possible explanation I can think of is that binoculars from same family share most construction parts (except for the eyepiece which takes care of magnification). This means that 7x, 8x, 10x etc. magnification binoculars from the same family use identical diameter objective lens. 42 would divide evently with 7 so my guess would be that same lens diameter comes from smaller (7x) binoculars but is used on larger models as well.

 

[JB in SC]

Eight power offers a good field of view with reasonable weight.

I've owned Leica products since the mid 80's and have been very pleased with them. My current is the Ultravid 8X42. Very durable and has an "easy" view, if that makes sense.

Any of the alpha binoculars are a pleasure to use and will spoil you. At that level, it's ususally very subjective as to which is "better" than the other.

The Better View Desired website is very good, sometimes a little dated. Alula, a Finnish birding magazine has some excellent articles (in English) that compare various binoculars.

http://www.alula.fi/

Best,
JB

 

[johnniet]

I now understand what happened.

My pupils are capable of opening to an aperature wider than 5.25mm. However, my eyes were not fully night adapted, hence it seemed as though no light was lost at an exit pupil of 5.25mm. However, had I allowed my pupils to fully open, I'd notice light loss through the binoculars.

You actually should see more light through the binoculars (with a 42mm lens to pick up light) than you would with your naked eye (with pupils maybe 7mm if you're lucky enough to be that young).

Here's a simple test: try looking at the stars at night. You should see a lot more stars with the binos than without.
The lenses take light over a large area but only from a small range of angles (probably 7-8 degrees at 8 mag.) At the eyepiece, you get the same light over a smaller area (the exit pupil is 5.25 mm) but it's coming from a wider range of angles (like 60 degrees) so that your eyes can distinguish the points better.

No light is created in the binocular, but you get more light from the direction you're interested in that you would with the naked eye.

If that's confusing, Cougar can probably explain it better.

[Added: how big is "big enough" depends on what you're viewing and the conditions. In good daylight you can get away with 30mm or less. In dusk or bad lighting you will get more out of the 42's.]