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What is more important transmission or exit pupil size as we age? (2 Viewers)

[email protected]

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I was thinking about getting a 10x50 binocular like a Meopta Meostar for low light use which has about 88% transmission, and then I got to thinking is it really going to have more apparent brightness than my Swarovski Habicht 10x40 GA which has 95% transmission but also has a 10 mm smaller aperture. It made me wonder how transmission and aperture interact. How much of an increase in transmission would it take to equal a 10 mm increase in aperture? Transmission makes the cone of light entering your eye brighter and of course exit pupil makes it bigger. As you age we all know your eye can not dilate as much, so you are only able to accept or utilize a smaller exit pupil, and you need 3x more light at 60 as you do at 20 years of age, so I am wondering if transmission doesn't become more important than exit pupil as we age. What do you think?
 

Jessie-66

Germany
Roughly speaking, in light twilight (eye pupil < exit pupil) the binoculars with higher transmission and higher magnification is more powerful, in deep twilight, moonlight the binoculars with larger objective lens diameter, light gathering power with equal transmission. The eye pupil diameter must use the exit pupil diameter, with this the whole aperture of objectives. Some binoculars have undersized prisms, allbinos checks vignetting and darkening at edge of field of view. Imho, for high demands on twilight performance, the exit pupil of the binoculars therefore should be slightly larger than the maximum pupil diameter of older and young human.

There are several empirical studies and indices calculated on them. In the German Wikipedia there is a whole article on the twilight performance of telescopes/binoculars, please use an online translator.
This picture is easy to understand, use online translator for professional terms:
 
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Alexis Powell

Natural history enthusiast
United States
...you need 3x more light at 60 as you do at 20 years of age...
To do what? To achieve similar visual acuity at randomly selected reading distances? Maybe. To see things when light levels are exactly low enough that the (population average) amount of age-related decline in pupil dilation would be exactly compensated by 3 times more light? OK, that would make sense (for that very particular set of conditions). To see things through bins in most circumstances, both in bright daylight and at a large range of lower light levels? I don't think so. I doubt that decline in photoreceptor sensitivity is very large with age. The decline in population average maximum pupil dilation is well documented, but it is also true that variation among individuals is so high that no one should assume that they cannot use a large exit pupil just because of age. Plenty of 70-year-olds have big pupils. Any serious observer will have this measured in order to make an informed decision.

If you are looking for a good rule of thumb given average people, typical birding conditions, and the products that we are typically selecting from among, I'd say aperture is almost always more important than transmission for best low-light binocular viewing performance. However, really good coatings and baffling are very important for good contrast, which is as or more important than brightness for being able to "see" things.

--AP
 

[email protected]

Well-known member
Supporter
To do what? To achieve similar visual acuity at randomly selected reading distances? Maybe. To see things when light levels are exactly low enough that the (population average) amount of age-related decline in pupil dilation would be exactly compensated by 3 times more light? OK, that would make sense (for that very particular set of conditions). To see things through bins in most circumstances, both in bright daylight and at a large range of lower light levels? I don't think so. I doubt that decline in photoreceptor sensitivity is very large with age. The decline in population average maximum pupil dilation is well documented, but it is also true that variation among individuals is so high that no one should assume that they cannot use a large exit pupil just because of age. Plenty of 70-year-olds have big pupils. Any serious observer will have this measured in order to make an informed decision.

If you are looking for a good rule of thumb given average people, typical birding conditions, and the products that we are typically selecting from among, I'd say aperture is almost always more important than transmission for best low-light binocular viewing performance. However, really good coatings and baffling are very important for good contrast, which is as or more important than brightness for being able to "see" things.

--AP
What do you think a good formula for transmission, exit pupil and age would be that would allow you to calculate which binocular would have the most apparent brightness? Would the Habicht 10x40 GA with 95% transmission have more apparent brightness than a Swarovski EL 10x42 with 90% transmission for a 65-year-old person?
 

[email protected]

Well-known member
Supporter
This article by Holger Merlitz might help you along.
Holger explains exit pupil, luminosity and contrast as it relates to binocular performance, but he doesn't touch on how the transmission of the binocular and pupil dilation affects target acquisition and seeing detail and that is what I am primarily interested in. What I would like to see is a formula using exit pupil, transmission and users age that would calculate which binoculars would have the highest apparent brightness. Good article though!
 
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[email protected]

Well-known member
Supporter
Roughly speaking, in light twilight (eye pupil < exit pupil) the binoculars with higher transmission and higher magnification is more powerful, in deep twilight, moonlight the binoculars with larger objective lens diameter, light gathering power with equal transmission. The eye pupil diameter must use the exit pupil diameter, with this the whole aperture of objectives. Some binoculars have undersized prisms, allbinos checks vignetting and darkening at edge of field of view. Imho, for high demands on twilight performance, the exit pupil of the binoculars therefore should be slightly larger than the maximum pupil diameter of older and young human.

There are several empirical studies and indices calculated on them. In the German Wikipedia there is a whole article on the twilight performance of telescopes/binoculars, please use an online translator.
This picture is easy to understand, use online translator for professional terms:
I agree that higher transmission, higher magnification and a larger objective diameter will improve seeing in deep twilight but which one is MORE important? Which one should you maximize if you want the best low light performance?
 

Jessie-66

Germany
I agree that higher transmission, higher magnification and a larger objective diameter will improve seeing in deep twilight but which one is MORE important? Which one should you maximize if you want the best low light performance?
In general, this is too complicated for me; one would either have to empirically determine and create a new index that includes transmission, aperture and ambient light, or calculate a mathematical multivariable / multisize optimization. Let's better stay with your concrete problem:
I was thinking about getting a 10x50 binocular like a Meopta Meostar for low light use which has about 88% transmission, and then I got to thinking is it really going to have more apparent brightness than my Swarovski Habicht 10x40 GA which has 95% transmission but also has a 10 mm smaller aperture.
I would simply calculate the percentage ratio of the AREA's (A = pi/4 * d^2) of the objectives (or exit pupils) from both binoculars. If this ratio is greater than the difference in transmissions, I would choose the binoculars with the larger aperture / objectives. This is under the assumption of deep (advanced) twilight. In this ambient light does a rather heavy and bulky 50 mm binocular make sense.
 
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henry link

Well-known member
It's not difficult to determine your own personal pupil dilation while looking through a binocular at any light level you choose. I've mentioned this technique many times over the last ten years, but it seems that most people don't want to bother.

All it takes is an artificial star, some masking tape and a large exit pupil binocular. The star should be defocused by setting the binocular focus at infinity or beyond and examining the star at a close enough distance so that the defocused star forms a round image of the binocular objective lens or the iris of the eye, depending on which is smaller. For simplicity this should be done with only one eye at a time. The measuring device is just two pieces of masking tape attached to the binocular's trim ring in front of the objective lens in such a way that there is an open slit between the two parallel tape strips. If the slit is visible through the binoculars then the eye is looking through a wider aperture than the slit. Adjust the width of the slit until the tape is barely grazing the edge of the defocused star on both sides and you have the diameter of the part of the objective lens that the eye is actually using. Divide that by the binocular's magnification and you have the diameter of your eye's pupil for that particular level of light when you are looking through a binocular.

I decided a few weeks ago to measure my current maximum pupil dilation in near total darkness with my eyes behind a pair of 8x56 binoculars. I set up an artificial star inside a storeroom in my garage at night. I positioned myself about 20 meters outside the open storeroom door. There was total darkness surrounding the star as viewed through the tripod mounted binocular and I used winged eyecups to block any dim lateral light from entering my eyes. The view was so dark I couldn't see the eyepiece field stop. The defocused artificial star was a dim gray circle, just bright enough to show the slit when the tape strips were placed on the objective ring. After adjusting the tape strips a few times I found that my current maximum dilation is about 5.2mm. When I first starting taking these measurements about 10 years ago my maximum dilation was about 5.8mm. I'm now almost 73.
 
I did it like this: set up a chair and my IR-converted camera with a remote release on a tripod in the closet.
Sat in the completely dark closet for 30 minutes listening to some music.
Switched on my IR flashlight (850 nm, just like the camera), held a steel engineering ruler on my cheek under my right eye - and took a picture.

On the computer blew the pic up to 100%, took some calipers to take the diameter of my dilated pupil and then held it against the ruler in the picture to read off the dilation: 6 mm.

Ergo I am looking at 10x56 binos (viz. #3) for my dawn/dusk viewing (or possibly even a 10x50 porro - I just lurve porros) as dawn/dusk will decrease my pupils' diameter. If I want something to see in the dark with I will get a proper nightview device.
 
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[email protected]

Well-known member
Supporter
I did it like this: set up a chair and my IR-converted camera with a remote release on a tripod in the closet.
Sat in the completely dark closet for 30 minutes listening to some music.
Switched on my IR flashlight (850 nm, just like the camera), held a steel engineering ruler on my cheek under my right eye - and took a picture.

On the computer blew the pic up to 100%, took some calipers to take the diameter of my dilated pupil and then held it against the ruler in the picture to read off the dilation: 6 mm.

Ergo I am looking at 10x56 binos (viz. #3) for my dawn/dusk viewing (or possibly even a 10x50 porro - I just lurve porros) as dawn/dusk will decrease my pupils' diameter. If I want something to see in the dark with I will get a proper nightview device.
I love porros too. What 10x50 were you looking at?
 

[email protected]

Well-known member
Supporter
It's not difficult to determine your own personal pupil dilation while looking through a binocular at any light level you choose. I've mentioned this technique many times over the last ten years, but it seems that most people don't want to bother.

All it takes is an artificial star, some masking tape and a large exit pupil binocular. The star should be defocused by setting the binocular focus at infinity or beyond and examining the star at a close enough distance so that the defocused star forms a round image of the binocular objective lens or the iris of the eye, depending on which is smaller. For simplicity this should be done with only one eye at a time. The measuring device is just two pieces of masking tape attached to the binocular's trim ring in front of the objective lens in such a way that there is an open slit between the two parallel tape strips. If the slit is visible through the binoculars then the eye is looking through a wider aperture than the slit. Adjust the width of the slit until the tape is barely grazing the edge of the defocused star on both sides and you have the diameter of the part of the objective lens that the eye is actually using. Divide that by the binocular's magnification and you have the diameter of your eye's pupil for that particular level of light when you are looking through a binocular.

I decided a few weeks ago to measure my current maximum pupil dilation in near total darkness with my eyes behind a pair of 8x56 binoculars. I set up an artificial star inside a storeroom in my garage at night. I positioned myself about 20 meters outside the open storeroom door. There was total darkness surrounding the star as viewed through the tripod mounted binocular and I used winged eyecups to block any dim lateral light from entering my eyes. The view was so dark I couldn't see the eyepiece field stop. The defocused artificial star was a dim gray circle, just bright enough to show the slit when the tape strips were placed on the objective ring. After adjusting the tape strips a few times I found that my current maximum dilation is about 5.2mm. When I first starting taking these measurements about 10 years ago my maximum dilation was about 5.8mm. I'm now almost 73.

So your Zeiss 8x56 FL really has no benefit for apparent brightness in low light. Ease of eye placement and less glare are the only advantages. Your NL 8x42 would be just as bright. For 73 a 5.2 mm pupil is pretty good! Interesting methodology though.
 

[email protected]

Well-known member
Supporter
In general, this is too complicated for me; one would either have to empirically determine and create a new index that includes transmission, aperture and ambient light, or calculate a mathematical multivariable / multisize optimization. Let's better stay with your concrete problem:

I would simply calculate the percentage ratio of the AREA's (A = pi/4 * d^2) of the objectives (or exit pupils) from both binoculars. If this ratio is greater than the difference in transmissions, I would choose the binoculars with the larger aperture / objectives. This is under the assumption of deep (advanced) twilight. In this ambient light does a rather heavy and bulky 50 mm binocular make sense.
Could you show how you would do the calculations? Math was not my best subject in school. Which binoculars would be better in low light?
 

Omid

Well-known member
United States
What is more important transmission or exit pupil size as we age?

Both quantities are overrated and their importance for "twilight viewing" is exaggerated. Here is why

a- Human eye does not perceive brightness proportional to the area of the eye pupil. This is due to an effect known as StilesCrawford effect of the first kind. The graph below shows the relative sensitivity of the cone receptors of human eye as the pencil of light entering the pupil gets larger. As you can see, the light that enters near the edges of eye pupil is much less effective in creating "perceived brightness".


SC_Effect.png


B- Human eye is not designed to respond to brightness. Brightness is not a characteristic of objects that we encounter in nature. Oranges, flowers and snakes don't have a characteristic brightness. They have a characteristic reflectance that defines their apparent color and texture. Our eye automatically perceives this reflectance and ignores brightness changes. According to Weber's law, human perceptual threshold for detecting a change in brightness is about 8%. This means, on average, people can not perceive a change in brightness less than 8% of a base level. This law implies that an increase of less than 8% in light transmission would be barely perceptible to most people, even those with young healthy eyes. Again, this is not the eye's fault. It is exactly what human eye is designed to do: ignore brightness (a highly variable quantity) and perceive reflectance (a stable feature of objects and environment).

C: Even if your eye pupil enlarge to 7mm or more, this may not help with resolving details in twilight. A wide open pupil increases the eye's intrinsic aberrations so visual acuity decreases. Human eye achieves maximum visual acuity at pupil dimeters about 2-4mm (Campbell and Gregory, Nature, Sept. 24, 1960, page 1122). At low light, the eye's acuity is very poor and it is independent of pupil dimeter (if artificially constricted).

D: Magnification can help the eye see better in twilight by enlarging the object such that it's spatial frequencies fall within the mid-level range of frequencies where the eye can still perceive and resolve details. That's why a 10X50 could be better than a 7X50 in some cases. Picture below shows how the eye's contrast sensitivity changes with spatial frequency. Spatial frequency is measured as number of black and white stripes (cycles) per visual angle (degree). Looking at a low contrast target, the eye can best discriminate spatial detail in the range of about 1 to 5 cycles per degree. Looking at high-contrast targets, the eye can resolve up to 60 cycles/degree.

typical-contrast-sensitivity-function.jpg

Sincerely,
-Omid
 

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[email protected]

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So what is important as we age? Would a Habicht 10x40 with 95% transmission or would a Meopta Meostar 10x50 with 88% transmission be brighter for a 60 year old birder? If transmission and exit pupil don't make that much difference the binoculars would have the same apparent brightness.
 
I love porros too. What 10x50 were you looking at?
Saying that the field is small would be the understatement of the year. Swaro's 10x40 is way off the mark at 4 mm exit pupil and only a 40 mil objective.
The other 'alphas' have reduced themselves to producing expensive and inefficient roof prisms only, so tbh I am looking straight at Nikon's Action EX 10x50 ATBs knowing fulwell the alpha-gang will probably explode with howls of derision; but dilligaff.

I have done quite diligent research into what works in optics, how and why, at least for me. And the days of playing quartets where that car whose top speed was 5 mph higher won, or of besting your best mate's dad's car with your dad's car, are long over.

Just like in hifi, cameras or watches theoretical value differences in the 1/100th and 1/1000th range are for people who prefer to gab rather than apply. Verbal onanism. Verbosely splitting hairs to cover up complete mental standstill.

So. Where are you at, binocularly speaking?
 
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[email protected]

Well-known member
Supporter
Saying that the field is small would be the understatement of the year. Swaro's 10x40 is way off the mark at 4 mm exit pupil and only a 40 mil objective.
The other 'alphas' have reduced themselves to producing expensive and inefficient roof prisms only, so tbh I am looking straight at Nikon's Action EX 10x50 ATBs knowing fulwell the alpha-gang will probably explode with howls of derision; but dilligaff.

I have done quite diligent research into what works in optics, how and why, at least for me. And the days of playing quartets where that car whose top speed was 5 mph higher won, or of besting your best mate's dad's car with your dad's car, are long over.

Just like in hifi, cameras or watches theoretical value differences in the 1/100th and 1/1000th range are for people who prefer to gab rather than apply. Verbal onanism. Verbosely splitting hairs to cover up complete mental standstill.

So. Where are you at, binocularly speaking?
I had a pair of Nikon Action EX 10x50 ATBs and they were actually quite good. They would put a lot of $700.00 roof prisms to shame. With a 6.5 degree FOV and being waterproof they are a good buy. Let me know how they work in low light because most porros have higher transmissions than roofs. A porro just kills most roofs for value. I think a 5 mm exit pupil is a good size for an all around binocular and no matter how old you are your eyes will dilate enough to use it. It is the 8x56 and 7x50 that becomes overkill.
 
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tenex

reality-based
I agree with Jessie and others here that seeing objects in low light is a matter of both aperture (whose effect varies more) and transmission. Also as Omid pointed out (though his other points are less relevant to this goal), magnification helps... so once you settle on 10x over 8x, you probably don't have to worry about lugging more exit pupil than you can use, even at your age. Just maximize aperture and transmission: big A-K's, SLC 10x56 (or perhaps HT 10x54, according to preference). It works for me.
 

[email protected]

Well-known member
Supporter
I agree with Jessie and others here that seeing objects in low light is a matter of both aperture (whose effect varies more) and transmission. Also as Omid pointed out (though his other points are less relevant to this goal), magnification helps... so once you settle on 10x over 8x, you probably don't have to worry about lugging more exit pupil than you can use, even at your age. Just maximize aperture and transmission: big A-K's, SLC 10x56 (or perhaps HT 10x54, according to preference). It works for me.
But what is more important aperture or transmission? Which one would be brighter for you the SLC 10x56 with about 92% transmission or the HT 10x54 with about 95% transmission. I bet the HT 10x54 would be brighter.
 

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