[01Foreman400]

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

[Matt_RTH]

This is a question with diminishing returns on either extreme. Short answer, I prefer exit pupil slightly larger than what I would expect in the light in the given situation. Any larger would be pointless, I reckon, though others may have a better answer.

Twilight factor (TF - square root of mag times aperture) is a good indication of what will be visible, but to me it is counter-intuitive. Say you have a 10x50 binoc which has a TF of 22, and a 7x42, which has a TF of 17. According to TF, the 10x50 will have more ability to discern detail. However, I would take the 7x42, due to field of view and the fact that I'd be able to discern motion more easily. Both should provide plenty of exit pupil. Then some would prefer the 10x50 due to the ability detect smaller movements or finer gradations in contrast (aka critters with natural camo). Different strokes. I guess with long distances, the 10x50 would still be more preferable.

[fugl]

Under most conditions (light beginning to fade at end of day, deep shade, etc) & if the comparison is a reasonable one (e.g., 8 x40 vs 10 x40), I would say magnification.

[ronh]

I have watched owls near dark a good bit. I've done ok with an 8x42, in fact an older and not particularly bright one. But the dim image was a strain on the eyes. I've also tried using a very good 10x50, but I found it annoying that the image jumped around so badly. The most comfortable low light view I've had is with a 7x50. Bright, steady, easy on the eyes. In a crunch a 10x50 might show a more detail, but I give it up gladly for viewing comfort.
Ron

[CLRobles]

Magnification! No doubt about it! I have time and time again proved this to people in the field who show up with 8x bins. Some with objectives as large as 50mm and still a 10x42 will out resolve in low light. The extra magnification just wins out every time...
The exit pupil argument would lead you to believe that a pair of 8x56's would be the ultimate low light bins right? Wrong! Although very good put them along side a pair of equal quality 15x60's and see which one resolves better! The 8x has a 7mm ep vs a 4mm ep of the 15x and yet the 15x resolves better in low light.....

[BobinKy]

Originally Posted by 01Foreman400

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

My vote and experience is for a large exit pupil. I second Ron's suggestion of a nice 7x50 with a 7mm exit pupil. The best is the Fujinon FMT-SX 7x50, however, it has individually focused eyecups. A good second would be the Vixen Foresta 7x50, which has center focus. The Nikon Action and Action Extreme 7x50 models are some budget models with center focus.

...Bob
Kentucky

[Alexis Powell]

Originally Posted by 01Foreman400

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

If the comparison is a reasonable one, magnification is unquestionably of greater value for seeing pattern/shape detail (generally the most important consideration in low light birding). Exit pupil might be more important if your concern is about preserving color vision for as long as possible as the light fades, but that is generally of lesser importance for making IDs.

--AP

[mooreorless]

Originally Posted by CLRobles

Magnification! No doubt about it! I have time and time again proved this to people in the field who show up with 8x bins. Some with objectives as large as 50mm and still a 10x42 will out resolve in low light. The extra magnification just wins out every time...
The exit pupil argument would lead you to believe that a pair of 8x56's would be the ultimate low light bins right? Wrong! Although very good put them along side a pair of equal quality 15x60's and see which one resolves better! The 8x has a 7mm ep vs a 4mm ep of the 15x and yet the 15x resolves better in low light.....

I agree, with the higher power [within reason of course] and enough exit pupil you are "closer" with the 15x than a 8x

Regards,Steve

[Tero]

As much as I have tried, I never see birds in detail enough to ID after it gets dark or dusk. I can see street lights and traffic signs better at 42mm than 32mm, but I am not interested in signs.

Dimness has been obvious in 10x25, 10x36 and some 10x42 models I have had. Winter cloudy days have been poor with 10x42. Scope at 50mm and 65mm still works on cloudy days.

[CLRobles]

When it come to low light observation it is all about resolution. Especially when it come to game observation. Almost all game observation is done at least at some distance. When observing game and trying to define antlers, horns, or even sex or species there is no way a lower magnification bin can define as well. Its not even close! I have been right there with 8x50 SLC's along side 10x42 SLC's and they don't come close! Also seen 10x50's next to 15x56's and they arn't in the ball park! Not even close! Sorry I'm a little passionate about this but I've been here down this road SO many times....
Its not just a guess on my part and I want the OP to get the right info here. When it come to low light observation of game.... Power IS the name of the game!
Of course all things need to be equal optically speaking. I'm sure a 10x50 Swaro would out perform a Tasco 15x

[Steve C]

Originally Posted by CLRobles

When it come to low light observation it is all about resolution. .... Power IS the name of the game!
Of course all things need to be equal optically speaking. I'm sure a 10x50 Swaro would out perform a Tasco 15x

I pretty well agree with this statement. Just about the only real use I put my 10x42 to is for low light. But The magnification becomes counterproductive without enough exit pupil. Put the same 10x30 quality against an equal 10x42, and the x30 is just not there. I see a lot of stuff about small exit pupils, but IF the glass quality is there 10x42mm will take me as far into the twilight as I have any business looking.

So about the only difference I have is that magnification is the trump card, provided the glass and coatings are up to the task. If not it matters not at all what the magnification or the exit pupils is.

[Tero]

Oh well, now we are talking game. That is a different game altogether.

[Kevin Conville]

Twilight Factor or one of it's variations is a somewhat better equation than the exit pupil squared answer for describing low light performance, but it's not perfect. Keeping within the bounds of what is generally used for handheld binoculars, magnification certainly is of greater importance to "seeing" in low light. The problem remains, as in good light, of being able to hold them still. Age of course, factors in as exceeding one's dilated pupil with the exit pupil of the bin does no good, excluding comfort.

There is no hard and fast rule for this as everyone is different but if you can hold them, go for higher mag, and let the aperture follow. The more, the merrier.

[Swedpat]

I would like to say that there is no absolute truth in this matter. To such a level magnification rules. But when it becomes enough dim for a given exit pupil the magnification doesn't help. For an example a 20x80 easily will outperform a 7x50 when it's not very dim. But when it has reached the level of dimness that the only thing you can see in the 20x80 is darkness, you still can see something in a 7x50. Because magnificated darkness=darkness.

The twilight factor is valuable within a limited area, because twilight factor is dependence of adequate exit pupil(relative brightness) for the current occation. A 20x80 has a higher twilight factor than a 7x50 and performs in many cases better for seeing details in lowlight. But according to the twilight factor formula an 80x20 has the same twilight factor as a 20x80. All of us who are knowledgeable in the optical rules understand that an 80x20 will be absolutely worthless in any lowlight condition, because a 0.25mm exit pupil will not even perform very well a sunny day, undependent of the optical quality!

Regards, Patric

[FrankD]

Which would you expect to be brighter in low light? An 8x56 or a 7x42?

[Swedpat]

Hi FrankD,

I suppose you post your question to me. The 8x56 is brighter because of the larger exit pupil, providing light transmission is equal or not much worse of the 8x56.

Regards, Patric

[Kevin Conville]

Originally Posted by Swedpat

I would like to say that there is no absolute truth in this matter. To such a level magnification rules. But when it becomes enough dim for a given exit pupil the magnification doesn't help. For an example a 20x80 easily will outperform a 7x50 when it's not very dim. But when it has reached the level of dimness that the only thing you can see in the 20x80 is darkness, you still can see something in a 7x50. Because magnificated darkness=darkness.

While I agree with you that there are no absolutes regarding this topic, I disagree (generally) with your assertion that at some point a 7x50 will out- resolve a 20x80. Even in the lowest of light, at any appreciable distance, the 20x80 will reveal more.

Exhibit A: Telescopes. I could use up to 200x with my Tele Vue 4" telescope when viewing planets under good seeing conditions. That's an exit pupil of .5mm and yet would resolve more detail than 100x and an exit pupil of 1mm. Closer to what we're talking about, I also have Fujinon 16x70 bins. They have an exit pupil of 4.4. I guarantee they will show you more at night, terrestrially and skyward, than 7x50s.

Originally Posted by Swedpat

The twilight factor is valuable within a limited area, because twilight factor is dependence of adequate exit pupil(relative brightness) for the current occation. A 20x80 has a higher twilight factor than a 7x50 and performs in many cases better for seeing details in lowlight. But according to the twilight factor formula an 80x20 has the same twilight factor as a 20x80. All of us who are knowledgeable in the optical rules understand that an 80x20 will be absolutely worthless in any lowlight condition, because a 0.25mm exit pupil will not even perform very well a sunny day, undependent of the optical quality!

Regards, Patric

There are limits to the usefullness of this formula Patric and playing with the Outer Limits (not the Twilight Zone ) has been used before to try to illustrate it's deficiencies, albeit at the extremes. That's why I said "Keeping within the bounds of what is generally used for handheld binoculars" and maybe should have said "anything one is like to see or use".

[Kevin Conville]

Originally Posted by FrankD

Which would you expect to be brighter in low light? An 8x56 or a 7x42?

A better example would be an 8x56 v 7x50 and, everything else being equal would place my money on the 8x56 for it's higher mag at the same exit pupil. Not much of a revelation here. A 10x70 would be better yet. That magical (and pervasive) 7mm exit pupil figure, unfortunately, only mostly works for the young. My eyes will only dilate to about 5.5mm, under the lowest of light. For me a 7x42 is as useful as a 7x50, for night use.

[mooreorless]

When I was testing the difference between a Nikon 10x42SE and a Fujinon 10x50 FMT-SX under evening light levels using USAF chart when it was dark enough I could still make out one of the elements in the 10x50 and not the 10x42 and when the 50 winked out I could always see the chart elements when I went to get the box it was mounted as I got closer. This was done over three evenings. BTW there wasn't a lot of time difference between the two tens.
Steve

[Swedpat]

Originally Posted by Kevin Conville

While I agree with you that there are no absolutes regarding this topic, I disagree (generally) with your assertion that at some point a 7x50 will out- resolve a 20x80. Even in the lowest of light, at any appreciable distance, the 20x80 will reveal more.

Yes, I think I agree, if we are talking of the lowest of visible light. Because when the 4mm exit pupil cannot more provide any detail to our eyes, a larger exit pupil may do it. And if we are actually see anything it's better though the magnification is lower, than a higher magnification of no visible detail...

Exhibit A: Telescopes. I could use up to 200x with my Tele Vue 4" telescope when viewing planets under good seeing conditions. That's an exit pupil of .5mm and yet would resolve more detail than 100x and an exit pupil of 1mm. Closer to what we're talking about, I also have Fujinon 16x70 bins. They have an exit pupil of 4.4. I guarantee they will show you more at night, terrestrially and skyward, than 7x50s.

I agree during the circumstances you mention below.

There are limits to the usefullness of this formula Patric and playing with the Outer Limits (not the Twilight Zone ) has been used before to try to illustrate it's deficiencies, albeit at the extremes. That's why I said "Keeping within the bounds of what is generally used for handheld binoculars" and maybe should have said "anything one is like to see or use".

I actually think there are no real contradiction between our statements! During most lowlight conditions the magnification and twilight factor rules when it comes to how much we can see. But if we go to the extreme it can be another thing.

Regards, Patric

[ronh]

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]

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]

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]

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]

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?