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New Binos (1 Viewer)

Lets be clear about twilight factor. It works providing the exit pupil or the pupil of the eye is not limiting. Holger explores it nicely (even if you can't follow the maths) in his paper which can be downloaded from this page. http://www.holgermerlitz.de/bino_performance/bino_performance.html

A 5mm exit pupil is probably adequate for most twilight birding (or hunting) needs. At this light level our eyesight would be typically 5 to 10 times worse than in bright conditions. You will need 5 or 10 times the magnification to see the same detail you would unaided in daylight. The 25% extra magnification of a 10x50 compared to an 8x40 entirely translates directly as an observable benefit in detail. With such poor eyesight the detail loss due to shake is effectively zero. The difference in transmission between a top of the range binocular and relatively cheap one is generally less than 10% these days which is not nearly so useful as increase in magnification. A cheap 10x50 (TF 22.4) will beat an expensive 8x40 (TF 17.9) when light or age dictates a 5mm pupil size.

The best I can get to these days is about a 5.5mm pupil. By moonlight my 10x56 (TF 23.7) allows me to see detail about 4 fold smaller than my best 8x42 (TF 18.3). My 12x45 has a TF of 23.2 but is easily beaten by the 10x56 in moonlight because the 3.75mm EP is limiting, however it still can compete with the 8x42 on detail due to the extra magnification. A young person who can manage a 7mm pupil will see more detail with an 8x56 (TF 21.1) in the lowest light than I will with a 10x56 because my pupil and the binocular exit pupil is limiting.

Hope that makes some sense.

David
 
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typo said:
With such poor eyesight the detail loss due to shake is effectively zero.

David
Click to expand...

Don't quite follow this bit David.

Due to unsteadiness there is a risk of loss of detail when holding a 10x compared with an 8x in full daylight, especially if there is a wind blowing, unless you have superman or wonderwoman arms. One would think this still applies in twilight or even more so since you are operating on the margins of visibility.

Lee
 
Lee,

In good light with an 10x binocular I could potentially pick out about a 1mm pattern detail but shake makes this about 40% worse so 1.4mm. If my eyesight is 10 fold worse due to low light then the smallest detail I could potentially see is 10mm but shake still only causes a 0.4mm definition loss so making it 10.4mm or 4% worse not 40%.

David
 
My exhaustive study of twilight factor has led me to these conclusions:

Twilight factor is a little, tweeting bird, chirping in meadow. Twilight factor is a wreath of pretty flowers that smell bad.

<B>
 
Sorry guys, the science observations behind the twilight factor is most certainly real. What got lost fron the original German puplications I understand is it's conditional on the pupil/exit pupil.

It's probably also true as well that most birders have more complex priorities and go home way before true twilight when the more dramatic differences are evident. I spent a weekend in the company of one of the UK's top birders a few weeks back. He has zero interest in optics and had been using the same10x42 (TF 20.5) for the last 15 years. It was in for a service and he'd been given a 8x32 (TF 16) as a loaner and he was finding he rather liked the lower power and wide view but was concerned about low light use and was considering getting a 8x42 as a replacement. We turned round and headed for base when I reckoned pupil diameters were 3.2mm. He stopped looking for small birds at 3.5mm and went indoors at I'd guess 4mm, but not before he'd compared it to the 10x42 I had with me. He conceded he was still seeing more detail with the 10x but not enough to encourage him to stay out longer. Twilight factor worked as it should, but he didn't bird in twilight. As a comparative novice I was quite content to spend a bit more time watching the flocks fly in to roost and look out for the barn owl I'd seen earlier. For a while the 10x42 was a better choice but as it got darker still the 8x42 had an advantage as the EP was limiting. Unfortunately I hadn't brought my 10x56 so I followed about 5 minutes later.

David
 
typo said:
Lee,

In good light with an 10x binocular I could potentially pick out about a 1mm pattern detail but shake makes this about 40% worse so 1.4mm. If my eyesight is 10 fold worse due to low light then the smallest detail I could potentially see is 10mm but shake still only causes a 0.4mm definition loss so making it 10.4mm or 4% worse not 40%.

David
Click to expand...

OK David got it.
But TF suggests more magnification is better while taking no account of the fact that as magnification increases so does your shakiness.

Lee
 
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I accept TF can be a rough guide but it comes with pitfalls.

It doesn't take into account the differences in quality of different bins and neither does it take account of how steady or otherwise you can hold bins. In addition as mentioned above, TF suggests more magnification is better (which will be true for some people) but this will increase shake for others. And this is without considering limiting factors as mentioned by David.

Lee
 
typo said:
Sorry guys, the science observations behind the twilight factor is most certainly real. What got lost fron the original German puplications I understand is it's conditional on the pupil/exit pupil.

It's probably also true as well that most birders have more complex priorities and go home way before true twilight when the more dramatic differences are evident. I spent a weekend in the company of one of the UK's top birders a few weeks back. He has zero interest in optics and had been using the same10x42 (TF 20.5) for the last 15 years. It was in for a service and he'd been given a 8x32 (TF 16) as a loaner and he was finding he rather liked the lower power and wide view but was concerned about low light use and was considering getting a 8x42 as a replacement. We turned round and headed for base when I reckoned pupil diameters were 3.2mm. He stopped looking for small birds at 3.5mm and went indoors at I'd guess 4mm, but not before he'd compared it to the 10x42 I had with me. He conceded he was still seeing more detail with the 10x but not enough to encourage him to stay out longer. Twilight factor worked as it should, but he didn't bird in twilight. As a comparative novice I was quite content to spend a bit more time watching the flocks fly in to roost and look out for the barn owl I'd seen earlier. For a while the 10x42 was a better choice but as it got darker still the 8x42 had an advantage as the EP was limiting. Unfortunately I hadn't brought my 10x56 so I followed about 5 minutes later.

David
Click to expand...

I believe it's real, it just doesn't matter to me.
 
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Troubador said:
I accept TF can be a rough guide but it comes with pitfalls.

It doesn't take into account the differences in quality of different bins and neither does it take account of how steady or otherwise you can hold bins. In addition as mentioned above, TF suggests more magnification is better (which will be true for some people) but this will increase shake for others. And this is without considering limiting factors as mentioned by David.

Lee
Click to expand...

The TF experiments were done in a time (100 years ago) when the transmission of a binocular was about 50-60%, and transmission of the blue spectrum even lower, and as Holger mentions in the article (linked above), experiments were biased towards higher mag bins.

Quality dimensions will always be lost when you try to put a single number on a complex issue.
TF might be an example of that.*

It's like putting a gourmet dinner in a blender and then serve it in a can with a spoon...
talk about not taking the observer into account...

*Just to clearify:
I have no problem with the underlying facts on vision in low light etc,
it's the model/formula (TF) I have problems with,
an 8x56 (with lower TF) will actually perform better than a 12x42 (with higher TF) if you are around 30 years or happen to have large pupils (see Holgers paper for the example).

So the bottomline is that TF might produce
false predictions on binocular performance
for a lot of people.
 
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It's not that I don't believe in Santa Claus....er. I mean... twilight factor, it's that at this point my acuity falls off rapidly in low light, so it doesn't help enough to matter, besides which, I'm a fair weather birder. If it's lousy outside, I'll find something else to do indoors like read Birdforum.

For diehard birders with younger eyes and hunters who pursue prey in the din of winter, I can imagine (but not see) how it might make a difference. Being that I came to birding via stargazing, aperture was more important to me then, but as a bird/nature watcher, weight and size assumed greater importance since I could handle a fairly heavy bin for stargazing since I was seated in one spot and the weight was shifted back on my face, but for birding, I was walking in the woods, carrying bins around my neck, so my priorities changed.

Now that I'm getting older and crickety, I've come full circle, preferring to find an open spot where I can set up a lawn chair and watch birds from a distance with the bins mounted on a monopod to keep my arms from getting fatigued. In the future, I would like to buy a higher power bin and use it on a tripod.

I still like lower power and wide fields for my backyard, but if I'm going out, why walk in the woods where I'm likely to see mostly the same species I can see in my backyard or in the nearby woods and risk getting bitten by a rattler? I'm no panzy, I once free climbed the Hudson River Palisades cliffs straight up. For the last six feet, I had to grab tree roots to pull myself up to the top of the cliff. If the roots had given way, I'd be six-foot under now. Eat your heart out, JT Holmes!:smoke:

In the open I can see birds I don't see in the woods such as bluebirds, BOP, turkeys, and the occasional heron or crane. I can also spot deer, porcupines, and once a black bear. When it starts getting dark, I pack it up because I can't see crap in dim light (and I don't like to step in it).;)

Brock
 
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Vespobuteo said:
The TF experiments were done in a time (100 years ago) when the transmission of a binocular was about 50-60%, and transmission of the blue spectrum even lower, and as Holger mentions in the article (linked above), experiments were biased towards higher mag bins.
Click to expand...

Very reasonable explanation - have not found a reference on who invented the term and when, but in a world where everybody builds porro bins without coating (except for some new stuff built by Hensoldt in Wetzlar called Dialyth), this simple model might actually work.

Joachim
 
Has anybody ever compared the 10x50 Swarovski SV to the 12x50 SV in low light? That would be an interesting comparison. I really think for a 50mm aperture or under the 10x50 is an excellent format for low light detail.
 
I was able to do a bit of Bat watching with my old Sapphire 8x43 last summer on a late evening with a sort of red, orange, pink afterglow as the sun had set.

The wide angle was definitely needed though as those little critters sure are fast especially when diving as they seem to have so much more maneuverability. They were about 100m away and if they had been any closer they would have been difficult to follow. Totally different from a bird. I recon they must actually pull few g's?

Anyhow that was good enough low light performance for me and I think this newer Sapphire 8x43 I have is even better in that respect.
 
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[email protected] said:
Has anybody ever compared the 10x50 Swarovski SV to the 12x50 SV in low light? That would be an interesting comparison. I really think for a 50mm aperture or under the 10x50 is an excellent format for low light detail.
Click to expand...

"In real life, target detection under low light is rarely resolution, but rather contrast limited. Wild animals, which are active under twilight conditions, are often well adapted to their environment (camouflaged) and represent targets of particularly low contrast. They remain hidden to the observer’s eye, even when their apparent angular sizes by far exceed the resolution limits of high contrast targets."

http://www.holgermerlitz.de/bino_performance/bino_performance.pdf
 
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