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Old Friday 15th April 2011, 23:10   #1
lulubelle
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Shallow depth of field in the 8x32 format

Obviously, there are many favored formats - each having it's own pro's & cons. However, I am curious if a shallow depth of field is common in the 8x32 format in general? Many seem to really like this format, but I would think that the percieved lack of depth would be a big detriment. Are there bins that seem to suffer more (or less) from this issue than others? If the shallow depth of field is a common issue, then where is the gain from using this format?
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Old Friday 15th April 2011, 23:36   #2
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I believe that it has been pretty well established here that Depth of Field is determined solely by the power of the binocular. That is to say, all binoculars with 8 power will have the same depth of field. So any 8x binocular you use should have the same depth of field when used viewing the same object at the same distance. Differences in the focusing speed of the binoculars however can create an impression of difference in depth of field as it may be more difficult to obtain fine focus with one of them.

Also you should know that that the lower the power of the binocular the greater it's depth of field will be. For instance, a 7x binocular will have much more depth of field than a 10x will have. This is good to know if you often look into the branches of trees for warblers and such. Much more area in front of and in back of the object you have focused on will be in sharp focus with the 7x.

8x binoculars are popular because they are a good compromise of good depth of field but with a bit more power than 7x.

Other people will add more information here and it probably will be easier to understand than my comments.

Bob

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Old Friday 15th April 2011, 23:51   #3
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I hope I didn't sound like an idiot in asking that question! I have read through the forums extensively (and after reading through so many, I forget which ones had the tidbit of info I am looking for) but didn't remember that detail. Not that I have a lot of experience, but my 8x42's seem to have a better depth of field than the 8x32's I tried(the focusing on each bin was vastly different, I admit). In reading throught the various posts in the forum, one of the outstanding comments regarding the 8x32's, seem to be concerning the shallow depth of field. I assume that perception of the depth of field or lack thereof bothers some more than others, much like color bias or CA. Perhaps the 7x42's is where I should be looking!

Please pardon my moment of stupidity!!!
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Old Saturday 16th April 2011, 00:17   #4
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Not stupid at all. Don't worry. From what you say, I think it was the difference in the focusing that gave you that impression. I noticed it early this evening while sitting on my deck looking at this years invasion of common grackles flying around my still leafless maple trees. I had my slow focusing 8 x 30 Nikon EII and my very fast focusing Nikon 8 x 32 LX L. It depended on where the exact spot of sharp focus was when I looked at a specific bird. Sometimes grackles on branches further back were in focus and sometimes not. I know if I had been using my 7 x 42 Trinovids things would have been easier.
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Old Saturday 16th April 2011, 04:34   #5
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Quote:
Originally Posted by lulubelle View Post
Obviously, there are many favored formats - each having it's own pro's & cons. However, I am curious if a shallow depth of field is common in the 8x32 format in general? Many seem to really like this format, but I would think that the percieved lack of depth would be a big detriment. Are there bins that seem to suffer more (or less) from this issue than others? If the shallow depth of field is a common issue, then where is the gain from using this format?
I think its a combination of the fast focusers they use today in midsized roofs (the LXL, for example, goes 6 ft to ∞ in the less than 1/2 turn) and the lack of 3-D effect that gives the perception of poor depth of field.

The pros for 8x32 roof format are FOV, close focus, weight, and size.

The 8x32 model usually has a wider FOV than the 8x42 model (in the case of the Nikon EDG, that only amounts to 1/10 of a degree, but that's an exception to the rule). The 8x32 LXL is 7,8* vs. the 8x42's 7*.

The close focus is usually better, most modern midsized roofs can be used for "butterflying" as well as birding, though here too, the latest and greatest full sized 8xs such as the SV EL, are closing the gap.

Lighter weight and more compact size are other benefits of the midsized format.

There are other trade-offs ("cons") besides a decreased perception of DOF in midsized roofs:

Greater CA due to the shorter FL (ED glass helps here)

They can be harder to hold steady for users with BIG hands (particularly closed bridge roofs)

They often have shorter ER than their full sized counterparts

They have smaller exit pupils than full sized bins. Not a problem in the Lone Star State, but it can be here in Bedford Falls (aka "Cloudy Valley"), particularly in the winter.

I've yet to try an 8x32 roof that could match the resolution of the full sized 8x in the same series.

As far as if there are bins that suffer "mooreorless" from shallow DOF perception...

8x32 LXL = more, 8x32 EDG = less
8x30 SLC = more, 8x32 EL = less

I don't find this perceived shallow DOF issue with Nikon 8x32 SE or 8x30 EII porros.

Brock

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Old Saturday 16th April 2011, 05:17   #6
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Laura,
Thanks for yet another opinion on depth of field. Seriously. I have thought way too much about this, and generally subscribe to the "scientific" party line that DOF is inversely proportional to the square of the hypotenuse, uh, I mean the magnification! But something else is going on.

My 8x42 Zeiss FL has a super fast super smooth hair trigger focuser, and I have to refocus between one view a mile off and the next view a mile off. I think Brock has something there about the focus control. I don't tweak my military individual eyepiece focus 8x32s as much as the larger Zeiss. Maybe my eyes just work harder with those, to spare my fingers.

I believe you, whatever.
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Old Saturday 16th April 2011, 05:18   #7
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Originally Posted by lulubelle View Post
Obviously, there are many favored formats - each having it's own pro's & cons. However, I am curious if a shallow depth of field is common in the 8x32 format in general? Many seem to really like this format, but I would think that the percieved lack of depth would be a big detriment. Are there bins that seem to suffer more (or less) from this issue than others? If the shallow depth of field is a common issue, then where is the gain from using this format?
Lulubelle,

There is often a bit of confusion using the term "depth of field," because it has a specific technical meaning and a different every-day meaning. The every-day meaning usually refers to the spatial sense of depth seen within the view using two eyes, i.e., the 3D or stereo effect. Is this what you are referring to?

I don't think the 8x32 format provides less perceived spatial depth, unless we consider Porro prism binoculars. In that case, for a given power, binoculars with bigger objectives will be wider spaced apart and will produce a greater sense of spatial depth. Images will also be perceived as slightly smaller, incidentally. A larger field of view will also enhance the 3D effect to some extent, because more distance cues are included in the scene. There, the smaller objective 8x32 will often have the advantage.

Ed
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Old Saturday 16th April 2011, 10:43   #8
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lulubelle,

thanks for the post-this is an informative thread

edj
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Old Saturday 16th April 2011, 10:52   #9
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If 8x32 has shallower depth of field than 8x42 : if top image is through 8x42 then the bottom one shows exaggerated version of what get through 8x32.
I believe that, in general, previous discussions on Birdforum seemed to conclude that this is not the case.

Source of picture :
http://www.photoshopsupport.com/phot...ld-pro-3-1.jpg

PS : BTW this wasn't intended as any sort of "QED" just a visual illustration of depth of field as "more stuff in focus front to back when both are focused at same distance". Can see how the OP's "percieved lack of depth" comment raises lots more discussion points.
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Old Saturday 16th April 2011, 23:36   #10
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Norm,

Yes, that is the case. Depth of field for a camera is, unfortunately, rather misleading for binoculars. Why? Because a camera is a focal system that projects an image onto a film plane or sensor. A binocular is an afocal system, which requires the human eye to focus the image onto the retina. Without the eye attached, the binocular itself has no defined focus, depth of focus, depth of field, or f-number. So what is it we see? We see the depth of field of the observer's own eye modified by the power of the binocular. That's why power is the only relevant binocular variable. Within that formal framework, the pupil of the eye takes on the role of defining the system aperture, not the objective diameter of the binoculars.

So if we are now talking about the technical definition of FOV that I mentioned above, there have been many discussions about it on BF. For reasons I won't go into, I don't think it's a particularly important feature to dwell upon because dynamic changes in the eye are always modifying the perceived FOV on a moment by moment basis. The dynamic relationships would require differential equations to express (that I haven't taken the trouble to work out), so I'd much rather stick with the day-to-day informal meaning(s), which do relate to design properties of the instrument. Several are mentioned in earlier posts.

Ed
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Old Sunday 17th April 2011, 00:47   #11
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The differences between the two pictures posted is actually a software generated synthesis of DOF produced by a Photoshop plugin. Pretty cool Sorry if you feel it was misleading; it was intended to give an illustration of a shortcoming the OP may have believed an 8x32 binocular might have for them when up against an 8x42.
In my PS above I think I indicated I was ready to accept I may have completely misunderstood what issue s/he was addressing
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Old Sunday 17th April 2011, 02:40   #12
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Norm,

Although you have provided a good example of depth of field in a camera, it is, unfortunately, very misleading for binoculars. Why? Because a camera is a focal system that projects an image onto a film plane or sensor. A binocular is an afocal system, which requires the human eye to focus the image onto the retina. Without the eye attached, the binocular itself has no defined focus, depth of focus, depth of field, or f-number. So what is it we see? We see the depth of field of the observer's eye modified by the power of the binocular. That's why power is the only relevant binocular variable. Within that formal framework, the pupil of the eye takes on the role of defining the system aperture, not the objective diameter of the binoculars.

So this is all about the technical definition of FOV that I mentioned above, and there have been many discussions about it on BF. For reasons I won't delve into, I don't think it's a particularly important feature to dwell upon because dynamic changes in the eye are always modifying the FOV on a moment by moment basis. I'd much rather discuss the day-to-day informal meaning(s), which do relate to design properties of the instrument. Several are mentioned in earlier posts.

Ed
Hello Ed,

A couple of pictures in my hallway, to dark outside, no eyes involved.

Picture one was focused at 8.5 meters, calculated DOF for the 10x optic was 1.42 meters, close distance 7.85 m, far 9.27 meters. The distance to the doorknob was 7 m, striker plate at 8.5 m and the far wall was 9.2 m.

Picture two was focused at 4 meters with the calculated DOF under 1 meter. Two door frames were approx. 1.5 m either side of the doorknob.

I will try to get more convincing pictures outside tomorrow.
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Old Sunday 17th April 2011, 03:00   #13
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RonE:
I am also wondering like Ed mentioned, about what these closeup type photos, usually with a camera, have in common with binocular viewing.

I am thinking most here are looking at birds at a distance and beyond, so what can we
learn from these ?

Jerry
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Old Sunday 17th April 2011, 03:21   #14
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Hi Ron,

If you attached a camera behind your binoculars you essentially created an approximation of a human eye coupled to it. It's called digibinning, right? In this case the power of the afocal binoculars modified the DOF of the camera, which is a focal system much like the eye.

I hope we're not confronting the idea that a binocular is an afocal system, or that an afocal system has no DOF. Maybe I'm slow on the uptake.

Regards,
Ed

PS. Jerry, the reason you experience a changed depth of field using binoculars (i.e., from normal vision) is basically the same as why your camera will show a changed depth of field when digibinning.
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Old Sunday 17th April 2011, 03:25   #15
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Originally Posted by normjackson View Post
The differences between the two pictures posted is actually a software generated synthesis of DOF produced by a Photoshop plugin. Pretty cool Sorry if you feel it was misleading; it was intended to give an illustration of a shortcoming the OP may have believed an 8x32 binocular might have for them when up against an 8x42.
In my PS above I think I indicated I was ready to accept I may have completely misunderstood what issue s/he was addressing
Sorry, Norm, my bad. I misunderstood what you were saying. I'll try to correct my previous comments.

Ed
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Old Sunday 17th April 2011, 04:25   #16
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Hi Ed, good to hear from you again.

I don't want to go through all this again and hesitated to even respond, so I will let you drive your truck and I will drive mine. The camera was focused to infinity for the afocal bino and these pictures. Very large camera DOF.

My thoughts. If there are no focal points (field stop, for instance) in the bino, then there should be no astigmatism, curvature or other focus errors in the image. Lens law dictates that the distance ahead or behind the object focus point puts the focus ahead or behind the image plane at the field stop. The eyepiece magnifies that real image and collimates the output. The only place the binocular is afocal is on the eye side of the ocular and when the desired objects are in focus, those ahead or behind the field stop of the ocular are still out of focus. When points are ahead or behind the field stop, then they are either converging or diverging at the exit pupil, i.e. focal.

Maybe I am just not understanding your comments about the lack of f#, etc.

Anyway, that’s my take on it. Have a good night.
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Old Sunday 17th April 2011, 05:30   #17
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Hi Ed, good to hear from you again.

I don't want to go through all this again and hesitated to even respond, so I will let you drive your truck and I will drive mine. The camera was focused to infinity for the afocal bino and these pictures. Very large camera DOF.

My thoughts. If there are no focal points (field stop, for instance) in the bino, then there should be no astigmatism, curvature or other focus errors in the image. Lens law dictates that the distance ahead or behind the object focus point puts the focus ahead or behind the image plane at the field stop. The eyepiece magnifies that real image and collimates the output. The only place the binocular is afocal is on the eye side of the ocular and when the desired objects are in focus, those ahead or behind the field stop of the ocular are still out of focus. When points are ahead or behind the field stop, then they are either converging or diverging at the exit pupil, i.e. focal.

Maybe I am just not understanding your comments about the lack of f#, etc.

Anyway, that’s my take on it. Have a good night.
Hi Ron,

I assume you mean the bino was focused to infinity rather than the camera. If you set your binoculars to zero diopters it will satisfy the lens equations as an afocal system. Now attach a camera to the back and only use it to focus. The camera's DOF will be modified by the power of the binocular. Assuming that the exit pupil of the binocular sets an upper limit on system aperture, it should be fairly easy to calculate the modified DOF of the camera at any working distance.

I'm not quite clear about what you mean by "...If there are no focal points (field stop, for instance) in the bino..." I'm talking about the system as a whole, not the lens elements inside. Yes, the objective and eyepiece are each focal systems and form images separately. When used together as a telescope, however, the total system is afocal.

I'm not enough of an optician to comment about the specific fate of aberrations through the instrument, but I don't believe the afocal nature of the binocular has much to do with it. The purpose of telescope design is to control these things by use of lens materials, shapes and distances. Some can be made to cancel and complex tradeoffs are required in optimizing programs. Now that you mention it, though, I guess afocal system aberrations would be completely irrelevant were it not for something focusing an image after the exit pupil, — e.g., the eye or a camera. That's probably why they call it a visual instrument. Of course, as we know, some aberrations of the eye itself also interact with those of the afocal instrument and are typically considered as part of the computer design. Three come to mind, ... curvature of field, distortion, and chromatic aberration.

Are we getting closer or farther apart my friend?

Ed
PS. Here are basic definitions: http://www.globalspec.com/reference/...and-telescopes
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Old Sunday 17th April 2011, 08:23   #18
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Hi Ed,

LOL, probably further apart.

No, the camera was focused at infinity. Always is when the binocular is focused at a finite distance since the exit pupil is collimated or, at least, focused to your visual requirements. I actually use fixed (inf) focus when testing except when I cannot properly focus the binocular. Hmmm, just the fact that you can adjust for individuals probably means the optics is not totally afocal, just that you can bring focus to users zero diopter point.

Anyway, enough of this thread. I just thought I would put my two cents in for a alternate view.
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Old Sunday 17th April 2011, 16:16   #19
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Hi Ron,

If you attached a camera behind your binoculars you essentially created an approximation of a human eye coupled to it. It's called digibinning, right? In this case the power of the afocal binoculars modified the DOF of the camera, which is a focal system much like the eye.

I hope we're not confronting the idea that a binocular is an afocal system, or that an afocal system has no DOF. Maybe I'm slow on the uptake.

Regards,
Ed

PS. Jerry, the reason you experience a changed depth of field using binoculars (i.e., from normal vision) is basically the same as why your camera will show a changed depth of field when digibinning.
Ed,

When you substitute a camera instead of the human eye, you lose another element in the human-bin optical train, namely, the brain, which processes the data and interprets it.

I don't know if there are any equations or even photographs that would shed "light" upon this perceptual phenomenon (unless you could tap into a person's brain like they did in the movie "Brainstorm"), other than to graphically approximate what one person says she sees vs. what another person says she see through the same two roof bins.

I don't think that an empirical test showing that the two bins being compared (8x42 vs. 8x32 of the same series) measure the same or nearly the same DOF invalidates Lulubelle's or anyone's perception of lesser of depth in the midsized version.

Something goes on between the bin and the observer that can produce different perceptions of depth, and reports of this are too widespread to be discounted.

I've mentioned some external reasons why midsized roofs in general could give a lesser perception of depth than their 8x42 counterparts, but my gut feeling is that where the actual difference resides is in the depths or shallows of our brain's convolutions as explained in this short article:

http://academics.tjhsst.edu/psych/ol...ion/depth.html

Of particular note are these comments near the end:

{It is the brain that must "compute" a 3-D representation of the scene. The brain can make mistakes in this process of designation of pairs! It is these mistakes which make possible the 3-D feeling that we get from viewing a stereogram.}

If the brain can make "mistakes" in interpreting visual cues that create a greater 3-D feeling than is actually there with a stereogram, then perhaps it can also take visual cues from a midsized roof and mistake them as having lesser 3-D feeling than is actually there.

Brock

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Old Sunday 17th April 2011, 19:16   #20
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Hi Ed,

LOL, probably further apart.

No, the camera was focused at infinity. Always is when the binocular is focused at a finite distance since the exit pupil is collimated or, at least, focused to your visual requirements. I actually use fixed (inf) focus when testing except when I cannot properly focus the binocular. Hmmm, just the fact that you can adjust for individuals probably means the optics is not totally afocal, just that you can bring focus to users zero diopter point.

Anyway, enough of this thread. I just thought I would put my two cents in for a alternate view.
We are diverging? You're a hard man to converge with, my friend, but my feeling is we are using the same concepts somewhat differently. The focus adjustment on the telescope does indeed make the system "focal" to some extent, but only to supplement the eye's cornea+lens, which does most of the heavy lifting. Going from infinity to near focus, the contribution (to focusing) of the telescope increases, and in so doing (according to various authors) this results in a residual effective afocal system (i.e., telescope) of greater power. As I recall, that's because the effective focal length of the eyepiece decreases. In any event, this is what I think you mean by "...focused to your visual requirements."

This is not a subject to be found in most optics books, but I did finally uncover a discussion of it, making reference to yet another author whose book was beyond my means, and probably intellect. Only if you beg on bended knee, repeatedly, will I try to find it again.

Warm regards,
Ed
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Old Sunday 17th April 2011, 20:02   #21
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...
1. I don't think that an empirical test showing that the two bins being compared (8x42 vs. 8x32 of the same series) measure the same or nearly the same DOF invalidates Lulubelle's or anyone's perception of lesser of depth in the midsized version.

2. Something goes on between the bin and the observer that can produce different perceptions of depth, and reports of this are too widespread to be discounted.

3. I've mentioned some external reasons why midsized roofs in general could give a lesser perception of depth than their 8x42 counterparts, but my gut feeling is that where the actual difference resides is in the depths or shallows of our brain's convolutions as explained in this short article:
Hello Brock,

Thanks for your many interesting thoughts, this being no less engaging than most. I mean that.

In responding to the first point, my position is that one never proves that there is no difference between two things, be they experimental treatments, performance of binoculars with different glass types, coatings, ...whatever. Why? Because 'no difference' is the null hypothesis, which in my religion of science is only accepted through lack of sufficient evidence to reject it. So, the ultimate question is not whether there is a difference if one looks hard enough, but whether the difference is large enough to be significant. This is the basis of statistical decision theory (of the Neyman-Pearson type.)

Perceptions of stereo depth, can be triggered by a great many visual stimuli and vary considerably between individuals. The real question is whether some of the variability is accountable to instrument parameters other than the ones I mentioned earlier. Lots of people draw incorrect conclusions from scant evidence, which is OK by me. I gave up on religious evangelism when I reached middle age. At that point I figured out that arrogance was a far better approach. LOL

With all due respect to the author, that short article was way, way, way too short, and not quite ... accurate. But I do think your gut feelings are relevant as much of our understanding points to the enormous capacity of the brain, which is not fully understood by any means.

Thanks again,
Ed
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Old Sunday 17th April 2011, 21:19   #22
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...When you substitute a camera instead of the human eye, you lose another element in the human-bin optical train, namely, the brain, which processes the data and interprets it.
Oh, I overlooked this point. Yes, I agree. Most folks don't wish to consider the biological side, and for those keenly interested in binoculars and telescopes it's often an annoying distraction. The brain, however, anatomically includes the retina of the eye, and a good deal of data processing is known to occur there. Too bad. It's like talking about a camera without interest in the sensor array. More is being discovered all the time, such as visual "receptive fields" that were only unearthed during our lifetimes. The properties of these biological structures have a great deal to do with the peculiarities of how we perceive, and how we adapt to visual stimulation. End of polemic.

Ed
PS. Delve into this at your peril. http://en.wikipedia.org/wiki/Receptive_field
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Old Sunday 17th April 2011, 22:54   #23
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I believe that it has been pretty well established here that Depth of Field is................................................ ............ .................................................. .................................................. ........

Other people will add more information here and it probably will be easier to understand than my comments.

Bob
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Old Monday 18th April 2011, 13:20   #24
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Bob,

I can’t speak for Ed but I believe we both believe that magnification is the overwhelming controlling factor of DOF, he can correct me if I am wrong. We just differ on the source.

Ed, Brock;

A couple of years ago I set out to prove what I was “seeing” with binoculars and other optics.

This turned out to be a rude awakening, at least as far as I am concerned. It turns out that what I see is not all that reliable; I think I see more what I “expect to see” rather than an “absolute” memory record.

Consider some of the following:

1: Studies in eyewitness testimony has become very suspect because of factors such as memory, suggestion and other outside factors. Turns out that eye witness identification in test scenarios is wrong a very high percentage of the time. I will not go into detail, but just one such study by Stanford (http://agora.stanford.edu/sjls/Issue...er&tversky.htm) is linked for reference. I follow this with interest because I testify in court a lot and talk to witnesses of accidents, property cases, industrial accidents, etc as an expert witness.

2: I used to be an avid reader (now days, I pick up a book and immediately go to sleep). When I am “in the zone” in a good book, I see the images in my mind, more like watching a movie. I do not remember the book at all, turning pages, etc. When I think of the story, I revisit the mental imagery, not the retinal image; I have absolutely no recollection of the actual book. I have to assume most readers have the same experience.

There seems not to be much of a correlation of what I actually see versus what I remember and “visualize”.

I am very surprised Brock, as a writer, has not made mention of this before.

3: Consider dreaming. Very clear imagery with no retinal input.

I have come to the realization that I am far more dependent and comfortable with devices that show measured data like light meters, spectrometers, CCD arrays and other hardware that shows, and repeats, levels and values.

They seem to be more reliable than what I “see”, which seems to change with every light level, my mood, or my state of fatigue.

Just rambling, been thinking of this for a while.

Best
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Last edited by Surveyor : Monday 18th April 2011 at 13:27.
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Old Monday 18th April 2011, 13:36   #25
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Bob,

I can’t speak for Ed but I believe we both believe that magnification is the overwhelming controlling factor of DOF, he can correct me if I am wrong. We just differ on the source.

Ed, Brock;

A couple of years ago I set out to prove what I was “seeing” with binoculars and other optics.

This turned out to be a rude awakening, .................................................

Just rambling, been thinking of this for a while.

Best
Ron,

I agree with you and Ed in your first sentence above about magnification and stated so in the deleted portion of my earlier post.

I was really just making a wry comment about my rather optimistic last sentence. No real criticism was intended. In fact I rather enjoyed the discussion. I hope Lulubelle did too.
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