7mm or greater exit pupil owners (1 Viewer)

[newfie ghost]

Curious, do any BF members have glass that has 7 or more mm of exit pupil? If so what are your impressions of this monster glass? E.g., 7x50, 8x56

Are they easy on the eyes? Bright? Excessive eye relief?

 

[FrankD]

You have seen my comments in the Vixen. I own/ have owned many 7x50s. They all share an easy view because of the great perceived depth of field and easy eye placement.

 

[ronh]

I have not seen, nor do I want, a finer viewing experience than my 7x50 FMT-SX presents, despite its bit of CA, and curved 53 deg apparent field. There is a bright calm immediacy about it that I can't put my finger on. But I just about give up trying to handle the 3.5 lb IF beast for anything approaching birdwatching. Life is about compromises they say, and the Fujinon is totally uncompromising.
Ron

 

[[email protected]]

Curious, do any BF members have glass that has 7 or more mm of exit pupil? If so what are your impressions of this monster glass? E.g., 7x50, 8x56

Are they easy on the eyes? Bright? Excessive eye relief?

I have tried several 7mm exit pupil glasses and I really don't see that much of an advantage. Your eye can only take in 4mm so the other 3mm is just there to make it more comfortable for eye placement. That is paying a big price in weight for eye placement! Carrying a tank around so your eye placement is a little easier.They are not really signifigantly brighter than a 32mm in daylight or even at dusk. Other than Astronomy they are not worth it and definitely not practical for birding. Alot of the old porro's had a 7mm exit pupil to gain brightness but with modern coatings you don't need it anymore. The DOF advantage is nice to look at but you don't need it for birding.

 

[Robert Wallace]

The 7x50 binoculars were designed for Naval (military) use and used mainly by young men in their late teens and early 20's with excellent eyesight who could fully utilise the 7mm exit pupil. I understand that our maximum pupil size is around 7mm when we are young.
Our eyes decline with age and your optometist/optician can easily measure your maximum pupil size, mine is less than 4mm the last time they were measured.
In a book about binoculars (which I have misplaced) the author, an American with a PhD in optics suggests buying binoculars with an exit pupil larger than your maximum eye pupil size is a waste of time. Without laboratory evidence, my own experience tends to agree with that suggestion. I see no difference in brightness between my 7x42s and 8x32s.
If I were to buy some new binoculars I might even be tempted to check out some 10x32s.
I agree binoculars with large exit pupils are easy to put to the eyes but is this a factor with experienced users, unless being tossed about in a small boat or yacht?
When I next meet with my friend who is a retired professor of Optometry I will raise the issue with him but this may not be until Christmas, unfortunately.

 

[Robert Wallace]

The book I referred to above #5 was
Choosing, using and repairing binoculars by J. W. Seyfried, 1995 published by the company he founded University Optics Inc, Michigan. Although referred to as Dr Seyfried there is no academic information added, so I cannot comment on his academic credibility.
The section of the book referred to is Why Age is a Factor pp 33-35.

 

[[email protected]]

The 7x50 binoculars were designed for Naval (military) use and used mainly by young men in their late teens and early 20's with excellent eyesight who could fully utilise the 7mm exit pupil. I understand that our maximum pupil size is around 7mm when we are young.
Our eyes decline with age and your optometist/optician can easily measure your maximum pupil size, mine is less than 4mm the last time they were measured.
In a book about binoculars (which I have misplaced) the author, an American with a PhD in optics suggests buying binoculars with an exit pupil larger than your maximum eye pupil size is a waste of time. Without laboratory evidence, my own experience tends to agree with that suggestion. I see no difference in brightness between my 7x42s and 8x32s.
If I were to buy some new binoculars I might even be tempted to check out some 10x32s.
I agree binoculars with large exit pupils are easy to put to the eyes but is this a factor with experienced users, unless being tossed about in a small boat or yacht?
When I next meet with my friend who is a retired professor of Optometry I will raise the issue with him but this may not be until Christmas, unfortunately.

Pretty much totally agree with you.

 

[newfie ghost]

I tried an old black scl 8x50 once. Not 7 mm but it was crazy.

I'd like to try the 7x50 vixen.

 

[Brigadier]

In a book about binoculars (which I have misplaced) the author, an American with a PhD in optics suggests buying binoculars with an exit pupil larger than your maximum eye pupil size is a waste of time. Without laboratory evidence, my own experience tends to agree with that suggestion. I see no difference in brightness between my 7x42s and 8x32s.

I agree; I can't see a difference in brightness between good quality 8x30-32s and 7x42-50s, even in dull light and shadow. And once you get to around 4mm exit pupil, eye placement isn't really a problem.

This reinforces my theory that, at normal binocular magnifications, 6-10x say, 32mm front lenses are big enough for birding.

 

[henry link]

Since I'm one of the few birders who uses an 8x56 I guess I'll have to be the one to explain why I prefer large exit pupil binoculars, even in bright sunlight. Turns out that they have some optical advantages in bright light that are overlooked in the simple view that exit pupil is “wasted” if it’s larger than the pupil of the eye. This has all been discussed here before, so I’ll just briefly list some of the advantages.

1) Greater viewing comfort: Large exit pupils are very forgiving of eye placement compared to small ones. I’m quite used to the easy view now, so ALL 4mm exit pupil binoculars feel overly sensitive to pupil placement.

2) Lower aberrations: Even when the optics are quite ordinary at full aperture, most 7mm exit pupil binoculars show very low aberrations when stopped down to 2-3mm by the pupil of the eye in bright light. Believe it or not, most any old 7x50 with a simple Kellner eyepiece will present the eye with lower axial aberrations in sunlight than the very best modern 8x32 in the same light. Off-axis aberrations in the eyepiece are also reduced because the edges of the stopped down objective lens light cone present easier angles to the eyepiece optics. That’s why ordinary Kellner eyepieces can show surprisingly good off-axis performance in old 7x50’s used in daylight. Finally defects, like astigmatism and pinched optics are usually confined to the outer half of the objective lens. The very same defects that would compromise an 8x32 in bright light may completely disappear in an 8x56.

3) High resistance to veiling glare: In bright light, even if there is an internal reflection at the edge of a large exit pupil it falls harmlessly on the iris rather than entering the eye. The very same reflection that causes flare in an 8x32 will be quite invisible in an 8x56.

4) Wider area of full illumination: All binoculars show off-axis vignetting from undersized prism apertures. At full aperture there is usually only a small area in the field center that actually receives light from the entire objective lens. In bright light the geometry changes, so that large exit pupil binoculars are less subject to off-axis vignetting that small ones. In bright sunlight my 8x56 FL shows almost no vignetting across the entire field while my 8x32 SE begins to gradually loose exit pupil around half way between the center and the edge. This is something of a mixed bag since vignetting can offer some of the same benefits to off-axis aberrations of an ordinary aperture stop down, but I think it may explain why large exit pupil binoculars sometimes seem "brighter" overall in daylight, even if light transmittance is no higher than a smaller binocular. They actually have effectively larger off-axis exit pupils even when the effective axial exit pupils are equal.

5) I've become quite convinced that I can hand hold my big 43 oz 8x56 steadier than smaller, lighter binoculars. The extra mass appears to dampen high frequency tremors, leaving a slower roll that allows glimpses of extra detail. They are certainly murder on the neck, so I use them with a harness and can hike all day with no complaint.

I'm so happy with my 8x56 that nothing else has come along in the last four years to tempt me. I suppose if I could custom design a binocular it would probably be a low aberration wide field 8x50, but there's nothing like that on the market now. I hasten to add that I never recommend my binocular or any other heavy 7mm exit pupil binocular to other birders. But, if like me, you want the absolute best and most comfortable optical image a binocular can produce in daylight you're stuck. I’m afraid even the finest pee-wee binoculars still can’t quite deliver it.

 

[newfie ghost]

Very interesting Henry, thanks. When I looked through the older slc, they did seem impressive despite the fact that they probably had the old coatings. Eye relief was insane.

Some folks say you can't take in more light than the size of the exit pupil relative to your pupil size. But why do my 42 s look brighter than my 32's in bright sunlight? Keeping the size of a hole constant, why can't you push more light through it?

 

[vop]

I'm 37, and my pupils easily opens up to +7mm in low light. I have measured them with a ruler and camera.

I totally agree about the ease of eye placement issues in 32mm binoculars. I find that 5mm EP is minimal for pleasant viewing.

Small binoculars of course have their advantages. But if not strictly limited by weight and size, bring at least 8x42mm binos.

I think:

1. People who do the gunslinger type of birding (throws the binoculars quickly up to the eyes, identify the bird and move on to the next target) find large exit pupil binoculars a waste.

2. People like me, who enjoy watching things for hours and on prefer low magnification big EP binos.

Am I right?

 

[vop]

...
Some folks say you can't take in more light than the size of the exit pupil relative to your pupil size. But why do my 42 s look brighter than my 32's in bright sunlight? Keeping the size of a hole constant, why can't you push more light through it?

I guess the "full illumination" part explains that. Or...?

 

[Troubador]

Newfie

Unless I am totally mixed up (not impossible) you can stuff more photons through the same sized hole.

An 8x32 has an EP of 4 but so does a 10x42 yet the latter has a significantly larger light-gathering area. So a 10x42 should look brighter than an 8x32.

Or have I just shot myself in the foot (again)?

Lee

 

[Hermann]

This has all been discussed here before, so I’ll just briefly list some of the advantages.

1) Greater viewing comfort: Large exit pupils are very forgiving of eye placement compared to small ones.

Agreed. That's a *huge* advantage of large exit pupils, and in my opinion the main reason why many people love their 7x42's so much. Compared to the ease of use all the other parameters (such as large field of view and large depth of field) are fairly insignificant in my opinion.

2) Lower aberrations: Even when the optics are quite ordinary at full aperture, most 7mm exit pupil binoculars show very low aberrations when stopped down to 2-3mm by the pupil of the eye in bright light.

Agreed. Many binoculars with large exit pupils have very high image quality in bright daylight, and the best of them are better optically than the best medium-sized binoculars.

3) High resistance to veiling glare: In bright light, even if there is an internal reflection at the edge of a large exit pupil it falls harmlessly on the iris rather than entering the eye. The very same reflection that causes flare in an 8x32 will be quite invisible in an 8x56.

While true I don't think this is *that* important in most birding situations. The resistance to veiling glare *can make a difference*, but the best of the smaller binoculars are already pretty good when it comes to dealing with internal reflections.

4) Wider area of full illumination: All binoculars show off-axis vignetting from undersized prism apertures. At full aperture there is usually only a small area in the field center that actually receives light from the entire objective lens.

I personally don't see any really significant difference here. The image as a whole just looks "nicer"; maybe the lack of vignetting contributes to this, but I don't know how much. I certainly don't notice the vignetting in the field. That's something I'll have to look at more closely in the field.

5) I've become quite convinced that I can hand hold my big 43 oz 8x56 steadier than smaller, lighter binoculars. The extra mass appears to dampen high frequency tremors, leaving a slower roll that allows glimpses of extra detail. They are certainly murder on the neck, so I use them with a harness and can hike all day with no complaint.

The weight is the killer as far as I'm concerned. I find I can hold binoculars weighing between 650 and 850 gr steadier than lighter or heavier binoculars, for instance when scanning the seashore or the edge of a wood for any length of time. It's only in high winds or on a boat that I find heavy binoculars easier to hold steady than lighter binoculars, and for my kind of birdwatching the big binoculars are just too heavy. As much as like good 8x56's or, better still, 8x50's, they're well above the weight I'm comfortable with.

Hermann

 

[Surveyor]

Turns out that they have some optical advantages in bright light that are overlooked in the simple view that exit pupil is “wasted” if it’s larger than the pupil of the eye. This has all been discussed here before, so I’ll just briefly list some of the advantages.

Hello Henry;

I agree almost completely with your five examples as to why large exit pupils rule.

I will also offer a sixth for consideration.

(6) The higher resolution, and hence, contrast (MTF) of the larger lens.

Folks can check this out for themselves by taking a small aperture and large aperture bino, of the same power, out and finding something like a distant radio tower or transmission line, something with a lot of straight lines in it. You will see the same thing through both as far as the cross members but the larger lens, even though no sharper at the edges of the cross members (limited by your eyesight) you should see them as being a little darker than the smaller lenses. This is the MTF (contrast) at work. Almost always will the larger be better unless a lot worse than the smaller example optically.

 

[stereotruckdriver]

Thanks Henry, as always good stuff!!! Always appreciate the depth of your posts as you explain things quite well! Bryce...:t:

 

[newfie ghost]

Newfie

Unless I am totally mixed up (not impossible) you can stuff more photons through the same sized hole.

An 8x32 has an EP of 4 but so does a 10x42 yet the latter has a significantly larger light-gathering area. So a 10x42 should look brighter than an 8x32.

Or have I just shot myself in the foot (again)?

Lee

That is what I thought, correct us if we are wrong

 

[Essex Tern]

I am very glad Henry Link has chipped in here, as I have been thinking about creating a post on "the wasted light issue" with large exit pupils, as it, especially with the recent discussions of lower powered bins, is a bit of a bug bear of mine.

Below are a few points I have been thinking about, some obvious, but I hope they all link up to my final conclusions.

In reference to the brightness of an image, given the same glass formulas, a lower magnification will give a brighter image, no matter what the level of light that you are in - this is not just a dusk thing. The other main factor to the brightness of the image would be the objective size, the more light entering, the more intense the light that leaves through the exit pupil, therefore you need as much area of glass up the front end as you can carry to let as much in as you can.

The exit pupil/eye pupil matching scenario is often quoted as during daytime the extra area of the exit pupil is wasted as your eye cannot match the size, however I do not believe this to be wholly true. I didn't really know why, but hopefully I may have stumbled across a possible solution.

The retina is based up of lots of rods and cones as we know, but the most important part of this is the fovea, which is responsible for our sharp vision. The surrounding cells are less accurate and deal with our peripheral vision.

With this in mind, the diameter of the fovea is quoted at around 1mm to 1 1/2mm - the fovea is directly at the back of the eye so I imagine that most of the light to meet this travels in pretty much a straight line through the cornea,pupil,lens and vitreous humour. I imagine nature hasn't done many complex light bending tricks with our lens and on the whole likes straight lines.

Using the above information I therefore propose that an ideal (if you could line it up successfully) exit pupil would be the same diameter as the fovea, i.e. 1 to 1 1/2mm. Everything above this is peripheral.

I can therefore see why at night, if your eye pupil could expand sufficiently to match a large exit pupil that this could be of use to transmit more light to the back of your eye, but the fovea, which does not change it's size, will still generally only see the same area of light - it is the large exit pupil which is a by product of a big front end area of glass, a low power, or both that produces lots of light, and that is why the image is brighter given ALL conditions - the intensity of light is the issue, not the size of the exit pupil, the size of the exit pupil is just a by product.

 

[Surveyor]

I personally don't see any really significant difference here. The image as a whole just looks "nicer"; maybe the lack of vignetting contributes to this, but I don't know how much. I certainly don't notice the vignetting in the field. That's something I'll have to look at more closely in the field.

Hello Hermann;

Concerning Henry's point 4 the attached jpg might help. This is how the light evens out when the exit pupil of a 8x42 bino has the exit pupil stopped down to 2.5 mm instead of the 5.25 mm normal. The dimmer off axis rays fall outside the eye pupil.

The top photo is of the full exit pupil while a totally diffuse light is applied, the second is just a 2.5 mm aperture inserted between the exit pupil and CCD.

Further details about natural vignetting can be found by Googling for the cos^4 rule of illumination.