01Foreman400
Member
In viewing animals in low light which is more helpful magnification or exit pupil?
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Magnification vs. Exit Pupil (1 Viewer)
- Thread starter 01Foreman400
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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.
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.
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
Ron
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.....
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
Well-known member
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
Natural history enthusiast
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
Well-known member
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
Retired
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.
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.
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
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
Well-known member
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.
Kevin Conville
yardbirder
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.
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.
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
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
Kevin Conville
yardbirder
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.
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
yardbirder
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.
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mooreorless
Well-known member
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
Steve
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...
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
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. :t:
Regards, Patric
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