Magnification vs. Exit Pupil (1 Viewer)

ronh · Sep 6, 2009

I'm the one who first said 7x50, but let me explain. The biggest most powerful thing you can hold, keeping the exit pupil around 5-6mm, will show the most detail in low light. But such a binocular becomes hard to enjoy after about 5 minutes. And if you're feeling stressed, rather than relaxed and happy, you might not see as much as theory says your optics will show.
Ron

BobinKy · Sep 6, 2009

8:00 p.m.
I go out to watch a squirrel gathing acorns at the top of a large oak tree 25 yards from my patio. I take a Fujinon FMT-SW 7x50 and Nikon SE 12x50. I see more detail of the squirrel, acorns, leaves, and bark with the Nikon SE 12x50. However, the squirrel is easier to follow, as he hops from limb to limb, in the Fujinon FMT-SX 7x50 due to the wider FOV.

8:30 p.m.
The squirrel is not around. So I focus on the dry brown leaves of the squirrel's nest. I give the edge to the Fujinon FMT-SX 7x50 because the brown in the leaves is more distinct. The bark on the oak, as well as the hanging acorns and the shiny green leaves, are more pronounced in the Fujinon FMT-SX 7x50 than the Nikon SE 12x50. But not by much. The Nikon SE 12x50 trails because the colors have taken on a muddy appearance.

9:00 p.m.
The full moon, the color of amber, is rising in the Eastern horizon. The planet Jupiter is visible with the naked eye. No stars are visible with the naked eye. I put my attention again on the oak tree. No contest. Definition of form and appearance of color is better in the Fujinon FMT-SX 7x50. The squirrel is no where to be seen. I turn the optics to the sky and the Nikon SE 12x50 puts the Fujinon FMT-SX 7x50 back in its place. The points of light (really reflections of light from our Sun) of the Moon, Jupiter, and his moons are larger and reveal more detail with the Nikon SE 12x50.

9:30 p.m.
I read where Kevin says the Fujinon FMT-SX 16x70 will outperform the Fujinon FMT-SX 7x50 terrestrially or in the night sky. I decided to put these two brothers to the test. The oak, bark, shiny leaves, and acorns, are more visible in the 7x50. I switch to a hedge row that does not have any visible sky behind, just the wall of a brick house. The prize, again, goes to the little brother--Fujinon FMT-SX 7x50--more detail is visible in the leaves and branches. The Fujinon FMT-SX 16x70 reveals nothing but murk. However, as expected, the little brother is put in his place when I turn the optics to the night sky. I see more craters in our Moon and notice all four moons of Jupiter with the 16x70. Jupiter's moons are lined up from left to right: Callisto, Europa, Io, and Ganymede. The 7x50 only detects three moons. Io, somewhere between 260,976 and 263,089 miles from Jupiter, closest of Galilean moons to Jupiter, discovered by Galileo in 1610, is not detectable with the 7x50.

10:00 p.m.
I go back outside with all three binoculars--Fujinon FMT-SX 7x50, Nikon SE 12x50, and Fujinon FMT-SX 16x70. The Moon is higher in the sky and takes on the a bright white color as she escapes the dust and moisture in the lower horizon. The Fujinon FMT-SX 7x50 shows Jupiter's moon Io, when I prop my elbows on the roof of my car to steady my hand shake. I turn my lawn chair around and face the apple trees of my next door neighbor, 50 yards away. With my naked eye, in the light of the moon, I detect the forms of three deer eating apples that have fallen from the trees. The deer come up from the Kentucky River, two miles away, to forage in the neighborhoods. Two nights ago, the tops of my tomato plants were chomped down a few inches. Tonight, I put the three binoculars to the test. Guess which binocular reveals the four points of a young buck? Yup, once again, the Fujinon FMT-SX 7x50 meets the low light challenge.

...Bob
Kentucky

Swedpat · Sep 6, 2009

BobinKy,

Interesting comparison you share! You also describe the important difference between lowlight use at earth and astronomical use. If you use the binocular for terrestrial objects and nature studies at dawn and dusk you practice lowlight viewing. But when you lift the binocular to the starry sky you practice bright objects viewing.

Regards, Patric

Surveyor · Sep 6, 2009

Excellent Bob, I might add that 8:01 was sunset and 8:28 there abouts was civil dusk at your latitude and on an average the light halves about every 5 minutes. Interesting post.

Best, Ron

Kevin Conville · Sep 6, 2009

That was an interesting report Bob, to the point you had me doubting myself!

So... I just spent 1/2 an hour A-B comparing Fujinon 16x70s against Leica 7x42 Ultravids. I don't have the 7x50 Fujinons and like I mentioned before, my eyes don't dilate to 7mm anyway so this is what I had to work with.

My findings are in stark contrast to what you found. Keeping in mind my 16x70s won't focus any closer than about 80', all comparisons were done at that distance or greater.

Really, no comparison at all. At anything that I could focus on, the big Fujis easily showed more detail. Block wall, foliage, distant street signs, shadowed license plates, whatever. All by moonlight. The magnification easily trumped any exit pupil advantage. Both bins were tripod mounted as well.

I have no explanation for the discrepancy Bob, other than possible shake or poor focus. I know focusing can be difficult in low light and the big Fujis really need some real estate to focus on anything.

Anyone else?

CLRobles · Sep 6, 2009

BobinKy said:
8:00 p.m.
I go out to watch a squirrel gathing acorns at the top of a large oak tree 25 yards from my patio. I take a Fujinon FMT-SW 7x50 and Nikon SE 12x50. I see more detail of the squirrel, acorns, leaves, and bark with the Nikon SE 12x50. However, the squirrel is easier to follow, as he hops from limb to limb, in the Fujinon FMT-SX 7x50 due to the wider FOV.

8:30 p.m.
The squirrel is not around. So I focus on the dry brown leaves of the squirrel's nest. I give the edge to the Fujinon FMT-SX 7x50 because the brown in the leaves is more distinct. The bark on the oak, as well as the hanging acorns and the shiny green leaves, are more pronounced in the Fujinon FMT-SX 7x50 than the Nikon SE 12x50. But not by much. The Nikon SE 12x50 trails because the colors have taken on a muddy appearance.

9:00 p.m.
The full moon, the color of amber, is rising in the Eastern horizon. The planet Jupiter is visible with the naked eye. No stars are visible with the naked eye. I put my attention again on the oak tree. No contest. Definition of form and appearance of color is better in the Fujinon FMT-SX 7x50. The squirrel is no where to be seen. I turn the optics to the sky and the Nikon SE 12x50 puts the Fujinon FMT-SX 7x50 back in its place. The points of light (really reflections of light from our Sun) of the Moon, Jupiter, and his moons are larger and reveal more detail with the Nikon SE 12x50.

9:30 p.m.
I read where Kevin says the Fujinon FMT-SX 16x70 will outperform the Fujinon FMT-SX 7x50 terrestrially or in the night sky. I decided to put these two brothers to the test. The oak, bark, shiny leaves, and acorns, are more visible in the 7x50. I switch to a hedge row that does not have any visible sky behind, just the wall of a brick house. The prize, again, goes to the little brother--Fujinon FMT-SX 7x50--more detail is visible in the leaves and branches. The Fujinon FMT-SX 16x70 reveals nothing but murk. However, as expected, the little brother is put in his place when I turn the optics to the night sky. I see more craters in our Moon and notice all four moons of Jupiter with the 16x70. Jupiter's moons are lined up from left to right: Callisto, Europa, Io, and Ganymede. The 7x50 only detects three moons. Io, somewhere between 260,976 and 263,089 miles from Jupiter, closest of Galilean moons to Jupiter, discovered by Galileo in 1610, is not detectable with the 7x50.

10:00 p.m.
I go back outside with all three binoculars--Fujinon FMT-SX 7x50, Nikon SE 12x50, and Fujinon FMT-SX 16x70. The Moon is higher in the sky and takes on the a bright white color as she escapes the dust and moisture in the lower horizon. The Fujinon FMT-SX 7x50 shows Jupiter's moon Io, when I prop my elbows on the roof of my car to steady my hand shake. I turn my lawn chair around and face the apple trees of my next door neighbor, 50 yards away. With my naked eye, in the light of the moon, I detect the forms of three deer eating apples that have fallen from the trees. The deer come up from the Kentucky River, two miles away, to forage in the neighborhoods. Two nights ago, the tops of my tomato plants were chomped down a few inches. Tonight, I put the three binoculars to the test. Guess which binocular reveals the four points of a young buck? Yup, once again, the Fujinon FMT-SX 7x50 meets the low light challenge.

...Bob
Kentucky

Bob I'm not stupid enough to tell you what you saw and to argue your post BUT..... I would have to see it to believe it. If indeed the 16x Fujinons have the same optics as the 7's I would have to say there is no way that they were out resolved by a bin the has less than half their power! Its just not possible! And you don't have to believe me. Pick up the phone and call any of the Alpha bin co's and ask what they recomend for resolving game at a distance with little or no light. I will bet my last dollar they will tell you the higher power bin will! Maybe Ben with Eagle Optics will chime in here and verify this as I'm sure he has spent time behind big Swarovski glass. Put a 8x56 SLC (one of the finest bins in the world) against a 15x56 in the field and try to resolve game at 300 yards. The 15x wins every time! Not even close! Try it again at 100 yards and the same result will follow. Maybe when you get at very close distances, say within 20-30 yards then the 8x might pull equal or show some things better but still not resolution. And this is a 3.73mm ep vs a 7mm ep. I would put my 12x SE's against any 7x at any time when it comes to resolving game at distance!

BobinKy · Sep 6, 2009

Kevin...

Please don't doubt yourself. This whole thread is pretty subjective anyway. I mean, there are just too many variables. I know my 7x50 out performs any other binocular I have in low light because I have compared them so many times before. But the whole thing hinges upon light. Doesn't it? And a rising full moon does brighten the landscape as it rises in the sky, as it has been doing this evening. And the last animal I compared was the buck deer eating in the full shade of an apple tree. . . . Pupil dilation is another variable. My dark-adapted pupils were tested last spring at 6.5mm by my eye doctor. She told me an interesting observation that in her practice, she has noticed that people with blue eyes retain larger pupil dilation as they age, than people with other color eyes. . . . The only way to really quantify this thread is with a light meter and resolution chart. . . . Oh well--it's 12:45 a.m. and I am off to bed. This has been a fun thread--the subjective ones always are!

...Bob
Kentucky

Matt_RTH · Sep 6, 2009

I just did a test. Informal, quick and probably wrought with errors

Full moon light, little other ambient light other than suburban glow.

Nikon 7x35E
Nikon 10x35E2
USAF test chart

Observation:
* I found it hard to detect actual difference in resolution visible
* 7x35 was definitely brighter, the chart seemed whiter, the chart had more contrast.

I think the thread has evolved with some key points:

Close range requires larger exit pupil and wider field of view
Long range requires a combination of exit pupil and magnification
Either one too extreme and the practicality is gone. I doubt anyone is hunting with a 15x56 or 15x70 except maybe on a tripod or with those nerves of steel.

BobinKy · Sep 6, 2009

CL...

I doubt if I can raise anybody at the alpha shops this time of night (12:55 a.m., Kentucky time). As I just explained to Kevin, this whole thread is about light, or the absence of light. It takes light for us to see anything, don't you agree? Anyway, this thread is so subjective. Maybe all of us will see it differently in the light of morning.

...Bob
Kentucky

ceasar · Sep 6, 2009

I think you have to consider the fact that the full moon is a fully sun lit object. If you were to take a photograph of it you would use the old "sunny 16" rule no matter what lens you used.

It is different from peering into poorly lit underbrush or looking at objects in late twilight conditions.

Bob

BobinKy · Sep 6, 2009

Matt...

Thank you for the full moon resolution test. I will certainly sleep better with visions of USAF charts dancing in my head.

Good night all!

...Bob
Kentucky

CLRobles · Sep 6, 2009

Matt_RTH said:
I think the thread has evolved with some key points:

Close range requires larger exit pupil and wider field of view
Long range requires a combination of exit pupil and magnification
Either one too extreme and the practicality is gone. I doubt anyone is hunting with a 15x56 or 15x70 except maybe on a tripod or with those nerves of steel.

To the contrary, every serious hunter I know, here in the west, has a high power bin between a 12x to 15x. Because of the great distances and the way one has to hunt in the west they have become the norm. A 10x around the neck, a 12 or 15x in the pack with a 60 to 85mm spotter along side it! Most hunters now will tote a 50 pound pack filled with optics and a tripod. Serious ones anyway...

CLRobles · Sep 6, 2009

ceasar said:
I think you have to consider the fact that the full moon is a fully sun lit object. If you were to take a photograph of it you would use the old "sunny 16" rule no matter what lens you used.

It is different from peering into poorly lit underbrush or looking at objects in late twilight conditions.

Bob

Exactly right, it is much harder to resolve with no moon light to help and maybe the reason Bob found his 7x's a winner? But even still the light is poor enough that looking into shaded objects at a distance should have had the 16x's showing more resolution?

CLRobles · Sep 6, 2009

BobinKy said:
CL...

I doubt if I can raise anybody at the alpha shops this time of night (12:55 a.m., Kentucky time). As I just explained to Kevin, this whole thread is about light, or the absence of light. It takes light for us to see anything, don't you agree? Anyway, this thread is so subjective. Maybe all of us will see it differently in the light of morning.

...Bob
Kentucky

I do agree that it takes some light to see anything BUT.... If you look at a dark object at 8 power and resolve it there, then you see the same object twice as close because you have twice the power you don't need the same EP. The power brings you closer so the smaller EP can still bring in enough light to out resolve...
Does that make sense to anyone but me :-O
Anyway the more power the less EP one needs to resolve...

Kevin Conville · Sep 6, 2009

ceasar said:
I think you have to consider the fact that the full moon is a fully sun lit object. If you were to take a photograph of it you would use the old "sunny 16" rule no matter what lens you used.

It is different from peering into poorly lit underbrush or looking at objects in late twilight conditions.

Bob

I purposely chose targets that weren't highly reflective and front lit. Looking into the shadows even with a bright moon is very low light indeed and I had to compromise to a degree as one needs adequate light to attain focus. The moon may need sunny 16 to photograph directly, but is 1/4 million miles away and isn't polished.

Kevin Conville · Sep 6, 2009

BobinKy said:
. . . Pupil dilation is another variable. My dark-adapted pupils were tested last spring at 6.5mm by my eye doctor. She told me an interesting observation that in her practice, she has noticed that people with blue eyes retain larger pupil dilation as they age, than people with other color eyes. . . .

I have blue eyes. I'm 53 and I'm myopic (wear contacts) but otherwise have healthy eyes.
I measured my pupils myself using the scale and flip the lights method and to my best estimate dilate to about 5 1/2 mm.

I agree that there are a number of variables.

Alexis Powell · Sep 6, 2009

BobinKy said:
As I just explained to Kevin, this whole thread is about light, or the absence of light. It takes light for us to see anything, don't you agree? Anyway, this thread is so subjective. Maybe all of us will see it differently in the light of morning.

Bob, as others have said, I can't tell you what you do or don't see, but for anyone reading this thread and supposing that this is entirely an open/subjective issue, please know that the question of whether a bit more mag versus a bit more exit pupil is generally more useful for seeing details (whether daylight, sun-lit planets at night, or dimly lit terrestrial objects) was settled a long time ago by users of telescopes and large binos, and it has been my experience that the conventional wisdom on this (that magnification trumps brightness because it is generally more useful to engage more of the retina than to provide more light to a given area of the retina) is correct. When I'm doing a big day and trying to make IDs of nearby shorebirds (that in daylight would be easily identified with 7x) at dusk and beyond, my 7x42 or 8.5x42 binos give out well before my 30x78 scope has lost its usefulness. Having a stable image is critical for these comparisons.

--AP

Matt_RTH · Sep 6, 2009

The spotting scope is an apt example, but it also illustrates truth in the exit pupil being every bit as important, again, on a sliding scale.

First, the OP question is related to Exit Pupil or Mag. So isn't it better to check the answer to the question by holding one variable constant? If you have the two being variable, then the effect of mag vs. exit pupil is at best skewed.

Which leads me to a point that anyone can with a spotting scope with a zoom can check.

Every spotting scope I have used, except for really large, top notch/alpha types breaks down at about 45x (often before). The view becomes unacceptably dark. Larger scopes that number will be higher. So if magnification, and only magnification improves what detail is visible, then a spotting scope should actually have a better image as one zooms in. Yet in practice we know that in most cases, the opposite is true. Not only does the angle of view become impractically small, the heat and atmospheric effects are more pronounced. Yet in absence of those environmental concerns, the dimness of excessive magnification is easily demonstrated. So exit pupil is obviously still important, with magnification.

I would love to see a better solution to this than just Twilight Factor, which factors in exit pupil, mag, objective size and available light. This is probably more like a torque and horsepower relationship where minimums exist to achieve acceptable performance. On one end you have the F1 cars running what, 15000 rpm and then on the other end you have a diesel truck running 1800 rpm and pulling a heavy load.

Kevin Conville · Sep 6, 2009

Matt says:
"Every spotting scope I have used, except for really large, top notch/alpha types breaks down at about 45x (often before). The view becomes unacceptably dark. Larger scopes that number will be higher. So if magnification, and only magnification improves what detail is visible, then a spotting scope should actually have a better image as one zooms in."

"Unacceptably dark" is subjective, but regarding this topic, is somewhat irrelevant. The topic is resolution, the ability to discern detail. One can have a dimmer high mag image and yet discern more detail than a lower mag, brighter image.

Also, no one on this thread said anything like "So if magnification, and only magnification improves what detail is visible..." That's silly.

The OP asked "In viewing animals in low light which is more helpful magnification or exit pupil?" In my answer I say, in effect, magnification first, aperture second but allowing for an optic that one is likely to use, that allows for enough light to get the job done and excludes the theoretical extremes.

"I would love to see a better solution to this than just Twilight Factor, which factors in exit pupil, mag, objective size and available light."

What else is there? Twilight Factor is not a perfect answer and really is best applied to commonly used optics, but I'm not aware of a better answer and trying to factor in environmental variables would be a "challenge"

BobinKy · Sep 6, 2009

Here are my "light of day" thoughts on this subject.

Without a doubt, the best optic will be the optic to show the level of detail required by the observer. But what is the level of detail required? Some are interested in an aesthetic balance of objects and environment during low light situations. Others are interested in the low light itself and how it effects the appearance of nature. And still others are more interested in the object itself, paying little attention to the environment and the low light, except to tolerate it as that is the condition of the time of observing. And on and on.

This thread started by asking about the observation of animals under low light situation. What kind of animals? Why as we observing the animals? What is the environment of the animals? How close can we get to the animals? Can we position ourselves so the animals will come close to our fixed position? What happens to the animals when we do manage to observe and identify them? What happens to us after the identification? These are questions that may be in the observer's mind--whether the observer be hunter, bird watcher, gardener, farmer, naturalist, or painter.

Personally, I place importance on light--specifically the aesthetic balance of light, life, and environment. To me a satisfying view includes all three in equal proportions.

I do not hunt or stalk animals per se (by, of, for, or in themselves). However, I can totally appreciate the optical needs of the hunter or birder. The observing goals of the hunter or birder are different than mine. My goals are closer to the artist or naturalist. Consequently, what satisfies me is different. I have many friends and relatives who are ardent deer hunters. To them, what is important is to see the deer and count the points on the antlers. During deer hunting season, they have one tag which means they can harvest only one deer. Some are interested in the trophy on the wall and bragging rights at the watering hole, while others are interested in filling the freezer with meat. Most are interested in both. More points mean a bigger head on the wall and more pounds of meat in the freezer. Their optical needs are different from mine.

The subject of magnification versus exit pupil gets to the heart of why many of us collect and use optics. Are we interested primarily in magnification, in a task or hobby which requires magnification? Are we interested primarily in light and the never ending balance of light and the appearance of things? Or, are our interests somewhere in between. Yes, I see magnification on one end of the question and exit pupil on the other end. To me it doesn't really matter if I have a quality binocular, spotting scope, or astronomy scope in my hands. What matters to me is the balance of light, life, and environment.

Your reasons and optics may differ--and that is good.

...Bob
Kentucky

Magnification vs. Exit Pupil (1 Viewer)

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