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Old Tuesday 4th June 2019, 04:36   #51
WJC
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Originally Posted by ceasar View Post
I think it is the same for all 6x's; all 7x's; all 8x's, all 10x's and on up the line.

Bob
Eronald:

Not only is ceasar as correct as he is succinct, but I would also suggest you read the article found at:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4461356/

It is part of an all-inclusive article by the US National Library of Medicine, published Oct. 2014 and I have attached the abstract. After reading the article, you will see why I have such fun talking about all the “BB stacking” that takes place on binocular forums. You will undoubtedly find the last sentence of the “conclusion” most interesting.

Bill
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Old Tuesday 4th June 2019, 12:50   #52
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The problem with roofs is focus asychronicity, aka focus slop.i have two roofs that don't focus both directions, only one way.Swaro fixed this with a spring, but folks didn't like that. I guess.

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Old Tuesday 4th June 2019, 15:55   #53
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Originally Posted by ceasar View Post
I think it is the same for all 6x's; all 7x's; all 8x's, all 10x's and on up the line.

Bob

In telephotos, mathematical depth of field depends on objective lens aperture and focal length. Subjective front and back depth of field, bokeh, and subjective separation depend on the actual lens design. This every photographer knows.

For binoculars, one could assume that dof will diminish with magnification and increase with smaller objective sizes. Thus an 8x20 could be expected to have much more dof than a 10x50 and won't demand much focusing near infinity, but also the 10x50 will pick a bird better out of the clutter of a tree-line :)

Also both sides of a bino can probably be focused slighly apart, the faulty setting actually increasing the subjective dof :) It might make sense to voluntarily mis-set the diopter slightly.

Edmund
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Old Tuesday 4th June 2019, 16:15   #54
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In telephotos, mathematical depth of field depends on objective lens aperture and focal length. Subjective front and back depth of field, bokeh, and subjective separation depend on the actual lens design. This every photographer knows.

For binoculars, one could assume that dof will diminish with magnification and increase with smaller objective sizes. Thus an 8x20 could be expected to have much more dof than a 10x50 and won't demand much focusing near infinity, but also the 10x50 will pick a bird better out of the clutter of a tree-line :)
Excellent observation. My impression is that magnification has a greater effect on DOF in binos than objective size, but it seems complicated because that isn't the same as aperture or speed ("f/?"). Does aperture in this sense vary much among binos?
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Old Tuesday 4th June 2019, 17:27   #55
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Quote:
Originally Posted by eronald View Post
In telephotos, mathematical depth of field depends on objective lens aperture and focal length. Subjective front and back depth of field, bokeh, and subjective separation depend on the actual lens design. This every photographer knows.

For binoculars, one could assume that dof will diminish with magnification and increase with smaller objective sizes. Thus an 8x20 could be expected to have much more dof than a 10x50 and won't demand much focusing near infinity, but also the 10x50 will pick a bird better out of the clutter of a tree-line :)...
To anyone interested in this topic, I recommend spending a day doing searches and reading from the archives of BirdForum. Much discussion of these topics suffers from misapplication of intuitions/assumptions that come from experience with camera lenses. Nevertheless, the topic of DOF in bins and scopes has been discussed in great and accurate detail here on BirdForum, including theoretically/mathematically, and through practical/experimental demonstrations. Long story short, binocular DOF is determined by magnification alone, not aperture or length or other factors. Magnification aside, the biggest variation in user experiences comes from how much eye accommodation users have, and perhaps, occasionally in some low light levels, how much their pupils open.

--AP
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Old Tuesday 4th June 2019, 17:46   #56
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Originally Posted by eronald View Post
In telephotos, mathematical depth of field depends on objective lens aperture and focal length. Subjective front and back depth of field, bokeh, and subjective separation depend on the actual lens design. This every photographer knows.

For binoculars, one could assume that dof will diminish with magnification and increase with smaller objective sizes. Thus an 8x20 could be expected to have much more dof than a 10x50 and won't demand much focusing near infinity, but also the 10x50 will pick a bird better out of the clutter of a tree-line :)

Also both sides of a bino can probably be focused slighly apart, the faulty setting actually increasing the subjective dof :) It might make sense to voluntarily mis-set the diopter slightly.

Edmund

The brain rarely works on mathematical principles and the workings of the physiological principles differ from person to person. I know people get tired of me talking about the physiological. However, as long as people try to skirt its realities, I will keep bringing it up. I thought that scientific/medical abstract would do the trick. Apparently not.

I know most want concrete—one size fits all—answers. Yet, those of us destined to live in the real world know that’s not a happening thing and it is never going to be.

The optical submarine periscope is being replaced by the electronic “photon mast.” Perhaps we could have eyes replaced by photonic sensors. That way things could be a LITTLE more quantifiable. But then, people would argue about who had the latest “Alpha” sensors.

Funny? Perhaps. Off the wall? Oh, yeah. Accurate? The track record says undoubtedly so.

Bill
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Old Wednesday 5th June 2019, 01:29   #57
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Hi, Patudo:

You, too, missed the point. You are speaking of a mechanical “Focus Drift,” not the more common physiological “focus drift.” I have covered the mechanical version at length. One of the attached is a snippet from my first bino book and the second is a graphic from one of my monographs.
The section of text from your attachment in your post #37 I commented upon relates to physiological, not mechanical focus drift. I quoted it in my post (#43) to make sure that was fully understood. Here it is again:

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However, let's say you have an accommodation range of 4 diopters and stop focusing the instant you have an adequate image. As time goes on, observing may become problematic because your natural (relaxed at that distance) focus setting should be -1.5 diopters. That means being in a hurry has placed your focus at an accommodatable, but strained, setting.
Now, if the above discusses mechanical rather than physiological focus drift, please let us know. (Funnily enough, the Cloudynights thread you requested your friend respond to with the above extract would seem to be an example of mechanical focus drift in the original poster's 15x70mm binocular, as he has no such issues with his other binoculars.) But, in any case, if observation is problematic or strained, should one STARE, and hope the image will improve by itself - or move that focus wheel, and do something about it?

I myself certainly experience physiological focus drift of a sort, in that my favourite spot is a fifteen minute walk from the bus stop and up six or seven storeys. That's nothing compared to the distances many of you travel, of course, but enough that after finding my target on (hopefully) my first look around the area, I'll have to tweak the focus to achieve the most effortless possible view as I cool off. I need to keep my target, normally 550m or more away, under observation until it flies, which could be as soon as five minutes but which might take a quarter of an hour or more. It's important that the image be as "easy", effortless, call it what you will, as possible while doing so, and to achieve that, I need to adjust the focus wheel - normally not by very much, nor very often, but some fine-tuning is almost always necessary. Granted, when using a 7x less fine tuning is required than with 8x or 10x because of the greater depth of field. But I really prefer to use one of the latter two when looking at pigeon-sized targets that distance away...

I use my accommodation when I have to - when the bird has taken off in hot pursuit and things are happening too fast to refocus. But for the much longer periods of waiting and watching, why on earth should one have to accommodate - when a tweak of the focus wheel can deliver a more relaxed view?

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Old Wednesday 5th June 2019, 04:03   #58
WJC
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The section of text from your attachment in your post #37 I commented upon relates to physiological, not mechanical focus drift. I quoted it in my post (#43) to make sure that was fully understood. Here it is again:



Now, if the above discusses mechanical rather than physiological focus drift, please let us know. (Funnily enough, the Cloudynights thread you requested your friend respond to with the above extract would seem to be an example of mechanical focus drift in the original poster's 15x70mm binocular, as he has no such issues with his other binoculars.) But, in any case, if observation is problematic or strained, should one STARE, and hope the image will improve by itself - or move that focus wheel, and do something about it?

I myself certainly experience physiological focus drift of a sort, in that my favourite spot is a fifteen minute walk from the bus stop and up six or seven storeys. That's nothing compared to the distances many of you travel, of course, but enough that after finding my target on (hopefully) my first look around the area, I'll have to tweak the focus to achieve the most effortless possible view as I cool off. I need to keep my target, normally 550m or more away, under observation until it flies, which could be as soon as five minutes but which might take a quarter of an hour or more. It's important that the image be as "easy", effortless, call it what you will, as possible while doing so, and to achieve that, I need to adjust the focus wheel - normally not by very much, nor very often, but some fine-tuning is almost always necessary. Granted, when using a 7x less fine tuning is required than with 8x or 10x because of the greater depth of field. But I really prefer to use one of the latter two when looking at pigeon-sized targets that distance away...

I use my accommodation when I have to - when the bird has taken off in hot pursuit and things are happening too fast to refocus. But for the much longer periods of waiting and watching, why on earth should one have to accommodate - when a tweak of the focus wheel can deliver a more relaxed view?
It is definitely about physiological.

“But, in any case, if observation is problematic or strained, should one STARE, and hope the image will improve by itself ...”

I said nothing even resembling that! You don't HOPE for anything.

Although I have beaten this dead horse ... to death, I will try, again.

If you learn to stare and be doing so while you are turning the focus knob, you will arrive at a RELAXED focus for that particular distance.

If you don’t do that, if you think it’s irrelevant, or think your opinion supersedes the realities of the matter, you will spend an inordinate amount of time fiddling with the focus. One over, one under, one on is appropriate for artillery ... not so good for optics.

Finally, he shouldn’t have to accommodate!!! That’s what I have spent a few hundred words trying to explain. If you don’t focus correctly, you must use accommodation. To focus correctly means to learn to stare and let the focus mechanism do its job. Although I want to be helpful, I have chased my tail long enough to see I’m not making any headway. Although I’m an old dog, I still haven’t learned I need not chase ever car that passes.

Bill
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