Magnification vs. Exit Pupil (1 Viewer)

BobinKy said:

Hey, CL--oh, buddy--did you read the replies over at 24hourcampfire? Don't they have a lot of "hunters" over there. I mean, what do you think about those replies?

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I did read their replies and I think most of them said that a higher power magnification bin with a usable EP of 4 to 5 mm (as I said a 10x42 = 4.2mm for the slower crowd) is what is preferred. I think one poster mentioned a 8x56, one post! I tell you what.... I cordially invite Bob, Ron, and anyone else who would like to go on a elk or deer hunt out to NM and I'll put you up and feed you and let you have a front seat lesson in low light glassing! Who's gonna come on down and take me up on this offer???? Then fell free to post to your hearts delight about what you have or have not learned!
And by the way Bob I'm not just going out and casually glassing little targets and trees in my back yard I'm actually out there! I'm actually out guiding people on hunts where low light game observation is actually taking place! Don't you think if a 7x42, 7x50, 8x42, or 8x56 worked better I would be using it? I have been in the field for the past twenty years, I think I know a thing or two about what works!
But I'm sure you have some property to sell us don't you!

CLRobles said:

I did read their replies and I think most of them said that a higher power magnification bin with a usable EP of 4 to 5 mm (as I said a 10x42 = 4.2mm for the slower crowd) is what is preferred. I think one poster mentioned a 8x56, one post! I tell you what.... I cordially invite Bob, Ron, and anyone else who would like to go on a elk or deer hunt out to NM and I'll put you up and feed you and let you have a front seat lesson in low light glassing! Who's gonna come on down and take me up on this offer???? Then fell free to post to your hearts delight about what you have or have not learned!

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Thank you for the offer! It certainly is tempting--and I sincerely mean it. I have not been in your lovely state since I camped at Philmont Scout Ranch, Cimarron, NM, in 1963. I did see some elk and bear on that trip. But the biggest animal memory was a skunk that came into our tent looking for food in the middle of the night. Man, let me tell you, we did not need any optics to identify that fellow. Luckily, we stayed still and he left without perfuming us.

CLRobles said:

And by the way Bob I'm not just going out and casually glassing little targets and trees in my back yard I'm actually out there! I'm actually out guiding people on hunts where low light game observation is actually taking place! Don't you think if a 7x42, 7x50, 8x42, or 8x56 worked better I would be using it? I have been in the field for the past twenty years, I think I know a thing or two about what works!

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Well, I am actually out there too! My "out there" is just closer to my back door. And the last time I checked, squirrels, deer, and rabbit were listed as "game" by the Kentucky Department for Fish and Wildlife Resources.

We do have quite a lot of deer in our state. The 2009 fall season estimated the population of white-tail deer to be 1 million with an annual harvest by bow, black powder, and gun hunters to be 100,000. I think New Mexico's estimated population is 250,000. However, you have us on the elk population: New Mexico has 90,000, while Kentucky only has 7400 with 1500 elk permits issued annually.

But no, I do not make a living by guiding people on hunting trips where low light observation takes place. If I did my priorities probably would change, for sure. As I have described in earlier posts, my current interests are more aesthetic observing (balance of light, animal, and surrounding). No, I not a tree hugger. But we do have quite a lot of trees to hug in Kentucky--18 billion cubic feet of timber on 11 million acres of forest land. I am sorry, but I could not find any stats on New Mexico's timber volume.

I am sure you know what works best in your terrain, which is quite different from the terrain we have here in Kentucky. I also know what works best in our terrain for the type of observing I like to do.

CLRobles said:

But I'm sure you have some property to sell us don't you!

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No, unfortunately, I had to sell all of my property to buy binoculars and scopes.

. . .

CL, I wish you the best with your next 20 years as hunting guide. It sounds a lot more interesting than what I find myself doing during retirement.

Take care.

...Bob
Kentucky

BobinKy said:

Thank you for the offer! It certainly is tempting--and I sincerely mean it. I have not been in your lovely state since I camped at Philmont Scout Ranch, Cimarron, NM, in 1963. I did see some elk and bear on that trip. But the biggest animal memory was a skunk that came into our tent looking for food in the middle of the night. Man, let me tell you, we did not need any optics to identify that fellow. Luckily, we stayed still and he left without perfuming us.



Well, I am actually out there too! My "out there" is just closer to my back door. And the last time I checked, squirrels, deer, and rabbit were listed as "game" by the Kentucky Department for Fish and Wildlife Resources.

We do have quite a lot of deer in our state. The 2009 fall season estimated the population of white-tail deer to be 1 million with an annual harvest by bow, black powder, and gun hunters to be 100,000. I think New Mexico's estimated population is 250,000. However, you have us on the elk population: New Mexico has 90,000, while Kentucky only has 7400 with 1500 elk permits issued annually.

But no, I do not make a living by guiding people on hunting trips where low light observation takes place. If I did my priorities probably would change, for sure. As I have described in earlier posts, my current interests are more aesthetic observing (balance of light, animal, and surrounding). No, I not a tree hugger. But we do have quite a lot of trees to hug in Kentucky--18 billion cubic feet of timber on 11 million acres of forest land. I am sorry, but I could not find any stats on New Mexico's timber volume.

I am sure you know what works best in your terrain, which is quite different from the terrain we have here in Kentucky. I also know what works best in our terrain for the type of observing I like to do.



No, unfortunately, I had to sell all of my property to buy binoculars and scopes.

...Bob
Kentucky

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Well my out there was at 11000 ft in dark Colorado timber of Pikes National Forest this morning... This is probably the toughest conditions a binocular can work in yet many do a very good job.... But one has to know which ones those are.... And I'm serious Bob, if you would like to come down I'd love to host you! I think you would have a great time here in the Rockies!

In terms of exit pupil, I propose the following rule of thumb for peak nature viewing.

Day light
1.5 - 3.0mm exit pupil -- spotting scope or astronomy scope
4.0 - 5.0mm exit pupil -- binoculars

Low light
3.0 - 4.0mm exit pupil -- spotting scope or astronomy scope
5.0 - 7.0mm exit pupil -- binoculars

I am sure there are many who may object to this rule for a variety of reasons, not the least being magnification playing second fiddle to aperture. However, this rule does attempt to quantify exit pupil choice somewhat.

Please post your comments.

...Bob
Kentucky

ronh said:

When it gets so dark that it's just flat hard to see, "resolution" is not the game, seeing something is. Under such conditions the view is lousy at best. But that would be, in the 7x50. Bob, you said this exactly right early in this thread. My comparisons concur. It's just a matter of how dark it has to get, and how much of the 7x50's light output your eyes can accept, before the "night glass" wins.
Ron

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At some point one can't see anything anyway. In my experience if there is enough light to focus on a subject, the big (16x70) Fujis (or similar) rule the night. Once light fades beyond that point, then what is the point?

I'm not doing much night surveillance myself.

The Fujinon in CL's pic is not the FMT-SX but the MT-SX, which is identical except for the eyepieces. In the non-F, the eyepieces are 3-lens Kellners, vs the 5-lens "flat field" design, the eye lens is smaller, the eye relief is shorter, and the edge correction may be a tad worse, but center field, they are optically equal.
Ron

Here is an link to an excellent thread--Exit pupil for night, exit pupil for day-- that appeared in the Cloudy Nights binoculars forum (2005). Among other things Holger Merlitz and others discuss the role of magnification versus exit pupil when observing animals in a dimly lit forest.

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=binoculars&Number=702093&Forum=,,,,,f33,,,,,&Words=exit%20pupil&Searchpage=5&Limit=25&Main=702093&Search=true&where=sub&Name=&daterange=1&newerval=&newertype=&olderval=3&oldertype=y&bodyprev=#Post702093

...Bob
Kentucky

ronh said:

The Fujinon in CL's pic is not the FMT-SX but the MT-SX, which is identical except for the eyepieces. In the non-F, the eyepieces are 3-lens Kellners, vs the 5-lens "flat field" design, the eye lens is smaller, the eye relief is shorter, and the edge correction may be a tad worse, but center field, they are optically equal.
Ron

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Thanks Ron, I really don't know what Fuji's they are or how well they would stack up against an SE.... I said in my previous posts that I didn't know which ones they were but I knew that they were a Fujinon 7x50 and that were newer than my Nikons, for what ever that's worth? They were actually a very nice bin once they were able to resolve and had some great qualities but they just were not a match against the SE in the low light... And this was the 10x42 SE, which does not do as well in low light as the 12x50. Although the 12x50 does not beat the 10x42 by much it does give you a couple more minutes and gives better detail throughout every low light situation.
I can't imagine how far ahead the 12's would have been over the 7x50 Fujinons!
I do know that after the hunt the hunter said "That's it, I'm getting new binoculars" and the funny thing is that the binocular he wanted was a Swarovski! The first thing I thought after the Nikon destroyed his bins were, what's wrong with my SE's! Haha, I guess I have really fallen in love with these SE's and the pride is starting to set in :-O But really they are that good! And although the EL's, Ultra HD's, and FL's are right there with them the SE's are just special and I really regret taking so long to find them!

BobinKy said:

Here is an link to an excellent thread--Exit pupil for night, exit pupil for day-- that appeared in the Cloudy Nights binoculars forum (2005). Among other things Holger Merlitz and others discuss the role of magnification versus exit pupil when observing animals in a dimly lit forest.

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=&Board=binoculars&Number=702093&Forum=,,,,,f33,,,,,&Words=exit%20pupil&Searchpage=5&Limit=25&Main=702093&Search=true&where=sub&Name=&daterange=1&newerval=&newertype=&olderval=3&oldertype=y&bodyprev=#Post702093

...Bob
Kentucky

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Bob, thank you for posting this! This is a great thread! I have to admit though, these guy's are way out of my league when it comes to the mathematics of the subject! Bob, I'm really a very simple man.... I'm just a Costco employee that loves the outdoors! I love everything about the outdoors and that's what led me here to BF. The love of the outdoors and wildlife go hand in hand with optics, high quality optics. I have for the last 20 years dedicated myself to spending 45 days in the field (minimum). I typically spend 60 to 90 days in the field a year. Mostly scouting, then hunting or birding (a new and strong love of mine) or guiding. What I have tried to do here on these posts is to pass on what I have learned on my road of optics. I have been fortunate enough to have worked for Swarovski (have seen their HQ and manu facilities) and have used virtually every high-end bin in the field extensively. I'm not bragging here, really I'm not. I'm just trying to bring the experiences of mine in the field to all here. I'll leave the opinion of my posts up to you the BF subscribers.... Maybe, just maybe, you all are thinking that I have some land for sale?
When reading this thread though, I had to think to myself "Holger is really incredible on the subject of binoculars, but really, what the heck does he know about hunting".... I really don't know, maybe Holger is a world class hunter that is in the field more than he is in the lab deconstructing optical instruments? Really I just don't know.... But I have said this before and I'll say it again. The Swarovski 15x56 is absolutely one of the best, if not the best, low light binoculars there is and it has a EP of 3.73!

CLRobles said:

Bob, thank you for posting this! This is a great thread! I have to admit though, these guy's are way out of my league when it comes to the mathematics of the subject! Bob, I'm really a very simple man....

I'm just a Costco employee that loves the outdoors! I love everything about the outdoors and that's what led me here to BF. The love of the outdoors and wildlife go hand in hand with optics, high quality optics. I have for the last 20 years dedicated myself to spending 45 days in the field (minimum). I typically spend 60 to 90 days in the field a year. Mostly scouting, then hunting or birding (a new and strong love of mine) or guiding. What I have tried to do here on these posts is to pass on what I have learned on my road of optics. I have been fortunate enough to have worked for Swarovski (have seen their HQ and manu facilities) and have used virtually every high-end bin in the field extensively. I'm not bragging here, really I'm not. I'm just trying to bring the experiences of mine in the field to all here. I'll leave the opinion of my posts up to you the BF subscribers....

Maybe, just maybe, you all are thinking that I have some land for sale?
When reading this thread though, I had to think to myself "Holger is really incredible on the subject of binoculars, but really, what the heck does he know about hunting"....

I really don't know, maybe Holger is a world class hunter that is in the field more than he is in the lab deconstructing optical instruments? Really I just don't know....

But I have said this before and I'll say it again. The Swarovski 15x56 is absolutely one of the best, if not the best, low light binoculars there is and it has a EP of 3.73!

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CL...

Thank you for telling us about your work and life--particularly your time with Swarovski. That must have been great!

Yes, Holger does know his optics. But, like you, I do not know what he knows about hunting. Since he spoke about hunters in a dimly lit forest, my guess is the terrain he describes is different from what you have there in New Mexico. The forests I visit here in central and eastern Kentucky are not open terrain, for the most part. For deer or elk hunting, a larger FOV, such as comes with many 7x and 8x, probably would be more important to hunters than magnification like the 15x. But, there are ravines where distance viewing is important. Of course, I imagine hunting along a forest's edge on cleared farmland is a different hunt altogether, and the 15x would be more appropriate. Most of the deer and elk hunters I know carry an 8x or 10x.

Please do not worry about the land selling comment. I should not have said what I said. Anyway, I meant it all in fun.

I hope you continue to share what you know with the rest of us. I know that I certainly need all of the optics knowledge I can get.

...Bob
Kentucky

I haven't read this whole thread, so this may have already been mentioned. The value of a large exit pupil surely depends on the maximum dilation of your own pupils in low light. This varies from person to person, and with age.

Someone who finds that high magnification/small exit pupil binoculars work better for them in low light than low magnification/large exit pupil binoculars, may in fact have pupils equal in size to the former. That would mean that for them the binoculars are equal, except in magnification.

Could this explain the different results people are getting?

pshute said:

I haven't read this whole thread, so this may have already been mentioned. The value of a large exit pupil surely depends on the maximum dilation of your own pupils in low light. This varies from person to person, and with age.

Someone who finds that high magnification/small exit pupil binoculars work better for them in low light than low magnification/large exit pupil binoculars, may in fact have pupils equal in size to the former. That would mean that for them the binoculars are equal, except in magnification.

Could this explain the different results people are getting?

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Thank you for your comments.

We sort of danced around the issue of maximum dilation of personal pupils during low light matching exit pupil size. However, I do not think we said it as well as you say it above. I think we kept this point at the personal perspective level and never got around to quantifying so much.

For myself, I have been measured by my eye doctor with dilated pupils at 6.5mm in an exam room with the lights out (my age is 60). But since this was within a minute or two of the lights going out, my guess is my dilation approaches 7mm after 15-30 minutes in the dark. I enjoy 7mm exit pupils in low light (twilight and heavy canopied forest) and think, at times, I see more of the landscape and shapes with the 7mm during low light than with more magnification and smaller exit pupils. However, as the backyard rabbit test describes above, halfway between sunset and darkness a few twilights ago, a 10x50 revealed the ears of a rabbit (50 yards away) where a 7x50 did not.

Others who report their personal dilation during darkness to be less, seem to prefer greater magnification over exit pupil for pulling out details.

Maybe, it is as you describe, the matching of exit pupil to eye pupil that has profound influence during low light, possibly more than greater magnification? Of course, as was mentioned by Surveyor in one of the posts in this thread, the light changes so dramatically between sunset and darkness (or sunrise to morning). What you can see in one minute may be totally different from what you saw five minutes before. A dimly lit forest is another matter, as the low light is more consistent over longer periods of time.

All in all, I find this to be a fascinating topic. I want to thank you and everyone else who participated in this thread. I wonder what the OP thought about our discussion?

...Bob
Kentucky

pshute,
I also imagine that has something to do with these discrepancies. Not just how wide one's eyes open up ultimately in near darkness, but also in those vaguely defined times called dawn and dusk. The 7x50's advantage is apparent to me only when it's practically night, and my eyes open up to about 6.3mm. It would be way too dark to make an ID, unless maybe a Great Horned Owl vs a Barn Owl.

CL,
I admit that I like my 7x50 for reasons that are partly emotional, hard to quantify, harder to defend, and not necessarily related to "performance". Maybe I see more through it than some people might just because I want to!?

But, what is it that hunters do with binoculars that's so different from what birders, stargazers, and landscape-watchers do? I Please give us a few instances in which the hunting usage is unique. (Use the "bullet" style of presentation if you like.)

Ron

ronh said:

, but also in those vaguely defined times called dawn and dusk.

Ron

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RonH;

Thought you might get a kick out of these links. Twilight is actually legally defined for a number of purposes.

http://aa.usno.navy.mil/faq/docs/RST_defs.php
http://en.wikipedia.org/wiki/Twilight

Best
Ron

ronh said:

The 7x50's advantage is apparent to me only when it's practically night, and my eyes open up to about 6.3mm. It would be way too dark to make an ID, unless maybe a Great Horned Owl vs a Barn Owl.

Ron

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Which is one of the reasons it is important to learn plant and animal sizes, as well as their silhouettes (stationary, and during flight or land movement), particularly if you do much low light observing.

As I mentioned in one of my earlier posts, I think the Fujinon FMT-SX 7x50 is quite good at bringing out the shapes of landscapes and the shapes of the plants and animals in those landscapes.

...Bob
Kentucky

Surveyor said:

RonH;

Thought you might get a kick out of these links. Twilight is actually legally defined for a number of purposes.

http://aa.usno.navy.mil/faq/docs/RST_defs.php
http://en.wikipedia.org/wiki/Twilight

Best
Ron

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Ron...

You come through again with all of the facts and numbers!

. . .

For those of you who are interested the USNO website that Ron referenced above, also has some calculators for you to calculate your own Sun rise, set, and various twilight times--by the day or for the whole year. Moon rise and set times can also be calculated.

From the following USNO site map, select the first two links under Data Services.

http://aa.usno.navy.mil/AAmap

. . .

Thanks, Ron!

...Bob
Kentucky

Ron,
Thanks for the twilight information. The navy document was especially enjoyable to read. The style is so clear, unhurried, and uncluttered. It has feeling of mental elbow room, and invites a mood of quiet contemplation.

Now I'm ready to go out to a spot in the country with a binocular, and just sit there while it gets dark.
RonH

Wow thanks for all the replies. I'll give a little back ground on me. I'm a deer hunter. Counting points in low light is my main goal. I'm looking for a pair of binoculars for over looking food plots and power lines from 100-500 yards. I've already got a pair of 8x30 SLC's, 10x42 SLC's and 8.5x42 EL's. After reading this thread I'm now thinking about buying a pair of 15x56 SLC's. I'm also 29 year old.

01Foreman400 said:

Wow thanks for all the replies. I'll give a little back ground on me. I'm a deer hunter. Counting points in low light is my main goal. I'm looking for a pair of binoculars for over looking food plots and power lines from 100-500 yards. I've already got a pair of 8x30 SLC's, 10x42 SLC's and 8.5x42 EL's. After reading this thread I'm now thinking about buying a pair of 15x56 SLC's. I'm also 29 year old.

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Get a Nikon 82mm ED scope, 25-75 zoom, and a 30X fixed eyepiece and you'll be counting hairs...in the dark. Even with a tripod this setup will cost less than a 15X56 SLC.
John

John Traynor said:

Get a Nikon 82mm ED scope, 25-75 zoom, and a 30X fixed eyepiece and you'll be counting hairs...in the dark. Even with a tripod this setup will cost less than a 15X56 SLC.
John

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Not true.... Although the premise is correct there is diminishing returns on the power that is usable especially in low light. If the scope were to be set on a fixed position it may very well pull in more resolution than the 15x Swaro's but the "fly in the ointment" is that while glassing for game in low light you must be using your bins in a grid like pattern constantly moving after a short scan of the location. Just too much to ask out of a spotter! Although not a 82mm scope my Swarovski 30x75 CTC will not do when glassing for game in low light! My 10x's do much better job! It would be WAY to hard to stabilize the spotter to get the optimal view....
Even with the 3.73 EP the Swaro 15x56 is the king of low light game observation!

BobinKy said:

The forests I visit here in central and eastern Kentucky are not open terrain, for the most part. For deer or elk hunting, a larger FOV, such as comes with many 7x and 8x, probably would be more important to hunters than magnification like the 15x. But, there are ravines where distance viewing is important. Of course, I imagine hunting along a forest's edge on cleared farmland is a different hunt altogether, and the 15x would be more appropriate. Most of the deer and elk hunters I know carry an 8x or 10x.

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It boils down to land... The western states have immense tracks of state owned land, national forests, and BLM land. Thousands and thousands of square miles of it. Whereas the eastern states have very little of that in comparison. A lot of eastern hunting is either still hunting or stand hunting but there is what is called "bean field" hunting and this would come closest to western hunting. In still hunting you would not begin to think of doing this before some kind of visible light so low light optics need not apply. In stand hunting you may very well get to the stand before light but the area is very close and a lower power bin can still resolve under these close range situations. In bean field hunting a hunter can still have to resolve game at distances of 500+ yards in very large ag fields, so a high power, high resolution bin would be needed and I would imagine a lot of 15X's are employed here....

ronh said:

But, what is it that hunters do with binoculars that's so different from what birders, stargazers, and landscape-watchers do? I Please give us a few instances in which the hunting usage is unique.

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As above its all about the amount of land that has to be scanned. Where as a birder is typically scanning canopies, shores, or close fields a western hunter will be, from a high point, scanning hundreds of yards out to miles in the distance. Its not uncommon to find game well before light that is 2 miles out! And this is before it is light out! Now imagine how well those top 15x's do at 50 yards! Its like day light out! They are that good at resolving in low light....