Magnification vs. Exit Pupil (1 Viewer)

[CLRobles]

Catch your breath and read the man's post. He's talking about food plots, power lines and 100-500 yard distances. That's not the wild west.

A 15X56 SLC weighs 45 ounces and I seriously doubt many will hand hold that much weight for extended periods of time. I'm sure everyone in "La La Land" does, but, in the real world, it just ain't so.

John

PS
I suggest you compare the respective surface areas of 56mm and 82mm objectives.

John sorry your still not right here! And who spoke of hand holding anything! No one is going to hunt a clear cut, or field, scanning 500 yards out, before light with a spotting scope! You would have to be in "La La Land" to think you could do so and spot as much game as you could with bin!!! Spotting scopes are just not used very much in the field anymore other than to judge trophy quality.
And I don't need to compare the surface areas, I'm well aware of what they are!
But once again I have reached a point of diminishing returns. Trying to pass on two decades of experience behind quality optics of every kind and shape....
I'm sure you know better so I will leave this thread to you!

 

[Pileatus]

John sorry your still not right here! And who spoke of hand holding anything! No one is going to hunt a clear cut, or field, scanning 500 yards out, before light with a spotting scope! You would have to be in "La La Land" to think you could do so and spot as much game as you could with bin!!! Spotting scopes are just not used very much in the field anymore other than to judge trophy quality.
And I don't need to compare the surface areas, I'm well aware of what they are!
But once again I have reached a point of diminishing returns. Trying to pass on two decades of experience behind quality optics of every kind and shape....
I'm sure you know better so I will leave this thread to you!

I wasn't originally posting to you but thanks for the arrogant response. It's convinced me once and for all to stop wasting so much precious time on BF.

For whatever it's worth, I can walk out the door, travel uphill through my forest, and within ten minutes be standing on a ridge with a power line. I'll actually be standing smack dab in the middle of a food plot that hosts deer, turkey, fox and an occasional black bear. The view is expansive, hilly, and ripe for hunting. I'm not a hunter, but all my neighbors are so my spotting scope is of some value to them during season. A large aperture scope with a wide low-power fixed lens works magic in this environment. I know because I've tripped in the darkness on the way home more than once.

John

 

[BobinKy]

Last twilight, five deer foraged in my back yard. I had some nice viewing with the Fujinon FMT-SX 7x50.

Should I feed the deer?

There are pros and cons to feeding deer in the back yard.

It is legal in Kentucky. However, it is illegal in other states, and some cities have passed local laws prohibiting deer feeding due to traffic accidents and the cost of carcass removal.

The pros are wildlife observing in your own backyard during twilight when the deer appear to be most active.

Any opinions on the matter?

...Bob
Kentucky

 

[mooreorless]

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.

Hello, I see that you do say you want to get a binocular and I have used the Swaro 15x56 a little in a good size field and found it an excellent binocular. You don't say you are going to try to find the deer, you already see them and want to "count" the points. There is a lot of difference from looking for game, birds etc. at the long distances that CL is talking about and trying to judge. My opinion is that you need a 80mm-88mm spotting scope for this or at least both a spotter and the big Swaro. We like to spend your money on this site. There are some dealers that will allow you to return binoculars, spotters after you try them so this might be a route to take. Good luck.

Regards,Steve

 

[BobinKy]

Hello, I see that you do say you want to get a binocular and I have used the Swaro 15x56 a little in a good size field and found it an excellent binocular. You don't say you are going to try to find the deer, you already see them and want to "count" the points. There is a lot of difference from looking for game, birds etc. at the long distances that CL is talking about and trying to judge. My opinion is that you need a 80mm-88mm spotting scope for this or at least both a spotter and the big Swaro. We like to spend your money on this site. There are some dealers that will allow you to return binoculars, spotters after you try them so this might be a route to take. Good luck.

Regards,Steve

Aw--shucks, Steve--why didn't you just say "go out and buy the Kowa 883 with 20-60 zoom."

 

[BobinKy]

Aw--shucks, Steve--why didn't you just say "go out and buy the Kowa 883 with 20-60 zoom."

And don't forget a nice observing chair with a side table for the Swarovski 15x56. :t:

...Bob
Kentucky

 

[FrankD]

One suggestion with the 15x56 Swaro SLCs...be sure the IPD will get down close enough for your eyes. The local Cabelas recently had a pair back in the bargain cave that I checked out. If I just used one eye the image was really quite good (looked just a bit dim in comparison to my Pentax 20x65) but I was unable to get acceptable image performancefor both eyes because the IPD would not adjust down low enough for my facial dimensions.

I have heard that the Vortex Khaibib 15x56 does go down lower.

 

[mooreorless]

Aw--shucks, Steve--why didn't you just say "go out and buy the Kowa 883 with 20-60 zoom."

Geez Bob you see right through my posts.

 

[CLRobles]

I wasn't originally posting to you but thanks for the arrogant response. It's convinced me once and for all to stop wasting so much precious time on BF.

For whatever it's worth, I can walk out the door, travel uphill through my forest, and within ten minutes be standing on a ridge with a power line. I'll actually be standing smack dab in the middle of a food plot that hosts deer, turkey, fox and an occasional black bear. The view is expansive, hilly, and ripe for hunting. I'm not a hunter, but all my neighbors are so my spotting scope is of some value to them during season. A large aperture scope with a wide low-power fixed lens works magic in this environment. I know because I've tripped in the darkness on the way home more than once.

John

For someone who doesn't hunt you sure as heck know a lot about it John! You sire are the arrogant one! I'm sure you can tell all the college and pro football coaches exactly what plays they should or should not have called from your armchair too! Your opinion that one should use a spotting scope to find game in low light is laughable and ignorant!

 

[Pileatus]

For someone who doesn't hunt you sure as heck know a lot about it John! You sire are the arrogant one! I'm sure you can tell all the college and pro football coaches exactly what plays they should or should not have called from your armchair too! Your opinion that one should use a spotting scope to find game in low light is laughable and ignorant!

One last time.

The poster said, "I'm looking for a pair of binoculars for over looking food plots and power lines from 100-500 yards."

Food plots and power lines are generally confined to narrow corridors quite suitable to scanning with a mounted scope, especially those equipped with wide angled lenses. Furthermore, I've actually used the 82mm/30X I mentioned to do exactly what the poster said he wanted to do. I don't care what anyone buys or uses in the field. Why should I? The point is a scope will do the specified job, the complete setup costs less than the 15X56, and it can be used in other situations where no binocular will "do the job". It's my opinion based on my field experience.

The respective objective areas are:
56mm Area=2463 square mm
82mm Area=5281 square mm

The 82mm scope gathers considerably more light than the 56mm, something that might be preferred in low light, especially if you're stationary.

John

PS
I said I don’t hunt, not that I never hunted. Did I mention football?

 

[Swedpat]

I find a discussion like this one to be very interesting. What I want to say is that the twilight factor is a mathematical formula which cannot be used in the same way like relative brightness index.
The exit pupil is the basic indicator of the perceived brightness of an optical instrument. When exit pupil becomes too small to provide any visible detail under a given occation the twilight factor loses it's value.

Often I read some statements who I cannot agree with.
For an example a 20x80 has twice the twilight factor of a 10x40. But is it better for low light conditions? I would say NO. I will explain what I mean. With the same exit pupil (and providing light transmission is equal) the perceived brightness is the same. The only difference is that you visibly come twice as close than with the 10x40. Which results in that you see more details, yes. But I cannot see how this has to do with TWILIGHT performance. In ANY circumstance the brightness allows you to see ANYTHING you of course will gain of higher magnification, day or night.
And if brightness is the same the comparison between the 10x40 and 20x80 will be exactly the same like if you are standing and with naked eyes observing an object at 10 vs 20m distance.
I would not explain this case that I with naked eyes can see more details at 10m distance than 20m because my eyes have better twilight performance at the shorter distance. But it's exactly what I do if I say that a 20x80 has better twilight performance than a 10x40.

BUT; I understand that the twilight factor has a point to make us understand that the ability to see details at low light conditions is a combination of brightness and magnification, mostly depending of the magnification. A 7x35 has 56% brighter image than a 10x40. 10x is ca 43% higher than 7x. In the most cases the 43% higher magnification outperforms the 56% higher brightness.

But still this isn't really the same as claiming that a 20x80 has better low light performance than a 10x40...

I know that what I am saying may be considered as controversial, but I welcome comments!

Regards, Patric

 

[mooreorless]

For someone who doesn't hunt you sure as heck know a lot about it John! You sire are the arrogant one! I'm sure you can tell all the college and pro football coaches exactly what plays they should or should not have called from your armchair too! Your opinion that one should use a spotting scope to find game in low light is laughable and ignorant!

Hi CL, Here is the quote from 01 Foreman 400 below, He has now said that he is counting points at 100-500 yds. I don't think it is laughable to use a spotting scope of 80mm and above to look in low light looking for or counting points on a deer. Saying that I do think he would be happy with the Swarovski 15x56 SLC. I would love the collection of Swarovski binoculars he has , small 8 a 10 and the EL.:t: It is hard to beat Swarovski's warranty. BTW I am not an armchair quarterback either.
Best Regards, Steve

"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."

 

[FrankD]

I don't want to further the discussion of whether or not a set of "Big Eyes" like the Swarovski SLC 15x56 is more well suited for low light observation over a spotting scope. That discussion has been discussed in detail on another forum that many of us frequent.

I will say though that I think the discussion of spotting scope usage in low light is highly underrated. I believe many of the comparisons of a spotting scope to a large set of binoculars is usually done with a zoom eyepiece attached to the scope. Considering how narrow the field of view can be on a majority of zooms I certainly can understand why one would prefer a larger binocular to it.

However, I have often made the comment that it would be an interesting comparison if one were to use a wide-angle, fixed power eyepiece on an above-average quality, 65 mm or larger spotting scope. The reason I mention that combination specifically is because I have spent countless hours behind a 20x65 wide angle spotting scope. I find the combination exceptionally high performing for scanning large areas for some very small objects for very extended periods of time.

Now, admittedly, my use of it in low light is limited. I decided to spend some time sitting out on the back porch last night with a 10x50, 8x56 and the 20x65 spotter. Of course the spotter provided details well after the other two "quit". I wish I had a pair of big eyes of comparable quality to see how a large, high powered binocular would compare to the scope in low light. I do have a binocular that might work. I will give it a go again later today/tonight and see what happens.

 

[Pileatus]

I find a discussion like this one to be very interesting. What I want to say is that the twilight factor is a mathematical formula which cannot be used in the same way like relative brightness index.
The exit pupil is the basic indicator of the perceived brightness of an optical instrument. When exit pupil becomes too small to provide any visible detail under a given occation the twilight factor loses it's value.

Often I read some statements who I cannot agree with.
For an example a 20x80 has twice the twilight factor of a 10x40. But is it better for low light conditions? I would say NO. I will explain what I mean. With the same exit pupil (and providing light transmission is equal) the perceived brightness is the same. The only difference is that you visibly come twice as close than with the 10x40. Which results in that you see more details, yes. But I cannot see how this has to do with TWILIGHT performance. In ANY circumstance the brightness allows you to see ANYTHING you of course will gain of higher magnification, day or night.
And if brightness is the same the comparison between the 10x40 and 20x80 will be exactly the same like if you are standing and with naked eyes observing an object at 10 vs 20m distance.
I would not explain this case that I with naked eyes can see more details at 10m distance than 20m because my eyes have better twilight performance at the shorter distance. But it's exactly what I do if I say that a 20x80 has better twilight performance than a 10x40.

BUT; I understand that the twilight factor has a point to make us understand that the ability to see details at low light conditions is a combination of brightness and magnification, mostly depending of the magnification. A 7x35 has 56% brighter image than a 10x40. 10x is ca 43% higher than 7x. In the most cases the 43% higher magnification outperforms the 56% higher brightness.

But still this isn't really the same as claiming that a 20x80 has better low light performance than a 10x40...

I know that what I am saying may be considered as controversial, but I welcome comments!

Regards, Patric

Patric,

The number of photons delivered to the eye is just a tad higher from the 80mm objective than the 40mm. Actually, the 80mm delivers four times the number of photons delivered by the 40mm.

John

 

[Swedpat]

Patric,

The number of photons delivered to the eye is just a tad higher from the 80mm objective than the 40mm. Actually, the 80mm delivers four times the number of photons delivered by the 40mm.

John

Yes John, you are right, but with twice the magnification this number of photons will spread out over 4 times larger area as well, which makes the image brightness to still be the same.

Regards, Patric

 

[Pileatus]

Yes John, you are right, but with twice the magnification this number of photons will spread out over 4 times larger area as well, which makes the image brightness to still be the same.

Regards, Patric

Patric,

The respective objective areas and exit pupils are:

56mm with 15X magnification
Area=2463 square mm
Exit Pupil = 3.73 mm

82mm with 30X magnification
Area=5281 square mm
Exit Pupil = 2.73 mm

When your eye dilates to 3.73 mm or more, both systems deliver all captured (shall we say redirected) photons to your retina. Some are surely lost in the abyss of each optical path, but you get my point. It's a factor of 2.1 (5281/2463) favoring, of course, the larger objective.

Also, when your eye is at 2.73 mm the 82 mm scope delivers all the photons from its 5281 square mm objective. The 56 mm bin exit pupil is masked, limiting its effectiveness to that of a 41 mm bin (2.73 * 15) with an objective area of 1320 square mm. Now, the ratio is 4-1 in favor of the 82 mm, but it's still probably bright enough no one cares. As darkness prevails and the human eye adjusts, both systems ultimately reach their maximum effectiveness. The light gathering ratio stabilizes at 2-1, in favor of the 82 mm.

If my calculations are wrong, please let me know and I'll make corrections.

John

 

[Swedpat]

Hi John,

I have no objection to your calculation. But I mean it concerns absolute brightness and not relative brightness. Light gathering power is not the same as how bright the image appears. The number of photons are as you say 4 times bigger with a 20x80 than 10x40 but this will not make the image to be brighter. It will just provide the same brightness with twice the magnification, and therefore it's comparable to looking at an object with naked eye at 10m distance instead of 20m. You will not see a brighter image because you come closer to an object, but providing the light conditions are adequate to see anything you will gain of it. And of course; it can be the deciding factor to see the detail or not. But I still will claim this has not strictly do do with twilight performance, because it's the same day or night.
I don't know if I misunderstand you, but you can tell me if so is the case.

Regards, Patric

 

[John Barber]

Low Light

In viewing animals in low light which is more helpful magnification or exit pupil?

In my experience, a good pair of 10 X 42 work best in low light.

 

[CLRobles]

I don't think it is laughable to use a spotting scope of 80mm and above to look in low light looking for or counting points on a deer. Saying that I do think he would be happy with the Swarovski 15x56 SLC.
Best Regards, Steve

Steve, I'll try to explain this one last time.... I have no doubt that a "Alpha" quality scope can pass on more detail in low light. I myself have a very good scope in a Swarovski CTC-75. A 75mm with a wide angle 30x eye piece. This scope does very well in low light and I have used this scope before in these tough situations.
The problem as I said before is it is very tough to use a scope like this. It is too hard to pan with the scope and get a stable image. It takes too much time for the scope to settle between the points and, with the extra power at hand, if you have to refocus it just makes it that much harder. When glassing for wildlife there is very little instances when you can just setup with your optics and view. They just don't like to stand still very long and are never predictable and like to come in from the least expected points.
Where the Scope is harder to use with one eye trying to find the game with a smaller, less stable FOV... The high power bin is a world more comfortable and usable to get behind. They are much, much more stable (allowing you to use them at their fullest extent), have a wider FOV that enables you to both find and stay on the game, and still have the resolution to bring in detail under extreme low light situations.

 

[CLRobles]

In my experience, a good pair of 10 X 42 work best in low light.

John you are right! A good quality 10x42 is on of the best low light bins out...