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View Poll Results: What about DOF?
I go by the numbers and the lens DOF scale. 48 36.92%
I try to consider all factors before pushing the button. 70 53.85%
I only use my 21 mm and at f22 at that. 0 0%
DOF??? All my photographs are out of focus anyway.... 12 9.23%
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What about DOF
Old 08-01-2006   #1
jaapv
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What about DOF

DOF: The reality of an illusion.

DOF is a subject that causes heated discussion in photographic circles. It is, of course, next to light and shape, one of the main photographic symbols to express ourselves.
There is a simple mathematical approach that is expressed in DOF scales on lenses and DOF tables in manuals, but, as always, that is not the whole story – by a fair margin.

DOF as a phenomenon is childishly simple. The human eye is a rather imperfect instrument for judging sharpness, so with a resolution of about 5 lp at 75 cm everything that is higher resolved appears sharp. So now the compications start. It readily confuses contrast with sharpness, the only reason that sharpening algorithms in postprocessing actually work.. So a photograph at noon at the beach will appear to have a deeper DOF than one on a misty morning. Of course, a photograph is, in reality sharp only in one plane, which is theoretically infinitely thin, but at least as thin as the state of correction of the lens and the quality of the receiving medium, be it film or sensor, allows. Lens manufacturers, in their quest for simplification and standardization have decided, in the 1920-ies, that an unsharpness of 0.03 mm on 35 mm film would be judged the measure of DOF. That leads us to the first set of complications.:
1. Without knowing the end enlargement of the photo one takes and without taking the contrast into consideration, judging the amount of DOF is actually rather hit and –mostly- miss.
2. As DOF is solely dependent on field of view, the “enlargement” of the focal length of the lens, which is responsible for the apparent deep DOF of wideangle-lenses and shallow DOF of long lenses gets into play, so the subsequent crop will influence the DOF in as much that if one crops a 28 mm shot down to the FOV of a 90 mm lens, the DOF will be exactly the same as that 90 mm lens would have produced.
3. Film is not without thickness. In reality a COC of 0.03 mm will act like a torch shining into a murky plate of soup. It will produce a cone, diffractions, reflections, if the light strikes the film at an angle it will turn into an oblong, etc., the net result being a larger diffuse spot. This is complicated by the fact that the films we have now are much thinner and higher resolving than we had in the 1920Ūes.
4. Digital sensors react far more like the ideal thin receiving medium than film, causing the COC’s to be even less diffused.
5. The net result is that the DOF produced now, and especially with modern lenses (of which I will write later) is more pronounced than it is historically. It is safe to assume that it is about 70% of the scale indicated on your lens. Btw. let’s not forget that it is not divided equally in foreground and background. The real division is, for simple mathematical reasons, 1/3-2/3, more or less, depending on subject distance.
All this caused me to call DOF in another context and another forum a RBU <rubber band unit>, which got me heavily flamed.

Then we get to the real controversial point, and that is the effect of individual lenses on DOF,
which relates to the elusive “boke”, which aptly translates to "chaos" or "confusion" I'm told, and to the rendering of out of focus picture elements.
In general the lens is corrected optimally for the plane of sharpness only, which means that aberrations like chromatic aberration and astigmatism increase quickly as sharpness decreases. Add this to my plate of soup effect and the magnitude of possibilities gets so large that only using the lens in practice will give any firm grasp of its (lack of) qualities.
The result is that, in extreme cases of not too well corrected lenses, there will be double contours, rings and general unpleasantness in the unsharp areas. That gives bad Boke. More elegantly, but still not optimally corrected lenses, and this applies to a large number of the older lenses used by RFF-ers, will produce generally soft and smoothly changing unsharp areas where the forms as such are undistorted. (did I mention geometrical distortion with the aberrations? This is the three-dimensional variant) That are lenses with a good boke. Then there are the newest, highly corrected lenses, like the Leica ASPH’s, APO’s etc. Those define the unsharp areas so well that they will break up the contours, giving rise to harsh boke.
Film will behave differently than sensors, as explained above. So a sweet lens on film may be unpredictably disappointing for digital and the other way around.

I have only scratched the surface of this subject here. Please add to this and contradict me as you please. If the thread does as well as the sensor size one, I’ll be happy
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Old 08-01-2006   #2
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Normally I only read threads that feature large print and big pictures. But I am going to make an exception. This looks interesting. Give me a little time but I will respond.
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Old 08-01-2006   #3
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Quote:
Originally Posted by kshapero
Normally I only read threads that feature large print and big pictures. But I am going to make an exception. This looks interesting. Give me a little time but I will respond.

I know, lots to read
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Old 08-01-2006   #4
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I have no problem with DOF on rangefinder, I was SLR shooter for long time and I can imagine
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Old 08-01-2006   #5
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>>I know, lots to read<<

But worth the effort.
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Old 08-01-2006   #6
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>>I have no problem with DOF on rangefinder, I was SLR shooter for long time and I can imagine<<

I think we in the SLR-era have it a lot easier than people back in the 1950s, who had a hard time visualizing depth of field.

I spent a lot of time with Nikomats and Nikon Fs, F2s and FM2s before getting into rangefinders. I knew the depth-of-field preview button was important, and I used it a lot. So by the time I was learning RF photography, I already knew how the lenses behaved.

On the other hand, lots of SLRs lenses have only very basic depth-of-field scales, especially those with really short focus throws. And depth-of-field preview buttons are only sort of accurate. You can't really judge critical focus with them.

Using rangefinders, I found that I developed a stronger understanding/comfort with depth of field. With an SLR you MUST keep the image in focus, or its -- by definition -- out of focus. And lenses with long focus throws are hard to fine-tune because you can't tell when it's really at it's sharpest (I never had good luck focusing the SLR version of the Nikkor 28mm/3.5). With the longer focus throw of Nikon/Kiev/Contax RFs -- and full depth-of-field markings for every lens -- I was able to visualize "zones of acceptable focus" and know that if the wide-angle-lens was set to, say, 6 feet, that I'd have acceptible focus throughout the room.

I now sort of visualize a "donut"-shaped layer of acceptable focus that surrounds me -- its width changes with each lens and can be expanded or contracted with the f/stop setting. It's a narrow paper-thin band with a 50/1.4 and a big fat bloated Krispy Creme thing with a 28mm lens. With SLRs, I spent a lot of time fiddling with focus. I have found I just don't need to do that with RFs, and that's probably I big reason I like them so much.
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Old 08-01-2006   #7
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ok I got halfway through that and it all went WAY over my head
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Old 08-01-2006   #8
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Quote:
Originally Posted by Ash
ok I got halfway through that and it all went WAY over my head
I looked at your gallery and I don't believe a single word of that statement.
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Old 08-01-2006   #9
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not a controversy for me in the least.

i decide before hand if i want shallow or deep dof and i completely ignore this made up crap about bokeh.
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Old 08-01-2006   #10
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Excellent article on DOF and perspective:
http://www.vanwalree.com/optics/dof.html

Scientific explanations with really informative graphs and example pictures, but with easy writing.

My favorite part of this article is the comparison of absolute blur and relative blur, which effectively illuminates the "telephotos have shallower DOF" notion. And he does it with pictures of a statue from Wallace and Grommit!
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Old 08-01-2006   #11
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Quote:
Originally Posted by back alley
not a controversy for me in the least.

i decide before hand if i want shallow or deep dof and i completely ignore this made up crap about bokeh.
Same here, although sometimes I wait until I see the print!!!
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Old 08-01-2006   #12
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Quote:
Originally Posted by jaapv
I looked at your gallery and I don't believe a single word of that statement.
Hah!!

I think I can use DoF correctly, (hehe I'm still working on bothering to meter correctly though!!) but the thread just seems like too much information. I'll stick to pagan photography. The sun goes up, you take a photo. The sun goes down, you party

None of this revolving round big balls of firey gas and distance/enlargement silver halide this that the other nonsense
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Old 08-01-2006   #13
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I am in the consider all factors camp. I like to view the lens tests as well as reading user opinions. jaapv's depth of field foray has answered questions I have been asking myself for quite some time. It explains why the bokeh, or (out of focus), areas are often "creamier" and described as more pleasing, with less well corrected lenses. This explains why some users prefer the third version to the fourth, or the regular version compared to the aspheric, and sometimes the original compared to the updated formula.
It appears as though most very highly corrected lenses are not conducive to progressively creamier bokeh. This does leave an opening for the designer to find the "sweet spot" here or to develop new designs to fill this niche. Maybe someone has one of these now and wishes to tell us about it?
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Old 08-01-2006   #14
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One of the most impressive examples I saw in the galleries of the use of DOF and selective focus as a symbol (and I hope Sam does not object to me linking to one of his photographs) is THIS ONE
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Old 08-01-2006   #15
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Quote:
Originally Posted by jaapv
One of the most impressive examples I saw in the galleries of the use of DOF and selective focus as a symbol (and I hope Sam does not object to me linking to one of his photographs) is THIS ONE
Perhaps Iím just not sophisticated enough, but what exactly is there to commend the OOF areas of that photo. No disrespect to the photographer, it is a legitimate subject.
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Old 08-01-2006   #16
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The symbolism of the barbed wire in focus in contrast to the normal-looking buildings, out of focus related to the history of that particular place. To me it condenses the whole story. Symbols are a personal thing, I suppose....
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Old 08-01-2006   #17
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What more is there to life?
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Old 08-01-2006   #18
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Excellent read Jaap, thanks. My vote for the "I go by the numbers and DOF scale". I am trying to master the DOF technique, lots of trial and error involved but I am surprised that I do get pictures in focus even when I am very doubtful I will. I actually used the technique with my SLR too (that's where it requires a leap of the imagination believe that you will get focused results, when you actually see through the viewfinder that your image area is unfocused) but I find the rangefinder lenses easier to work with (they have more evenly scattered markings on DOF).
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Old 08-01-2006   #19
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What more is there to life?
Other than longboarding and girls? Nothing I wanna know about
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Old 08-01-2006   #20
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1. I very much doubt sensors are any better than film at depth of field other that film has to be held flat. Sensors produce halos of varying pretty colors and often create hard color book lines in compression.

2. Depth of field is governed by length of lens, more means less, speed of lens, more means less, and aperature, less means more.

3. If one is in a critical depth of field situation, and has the time, just read the convenient little numbers that come with the lens otherwise the rule is: from the point focused upon the depth of field is 1/3 in 2/3 out and do the best one can (the total span in feet/meters as gauged on the lens).

4. Bokeh is a gift from God and because most lenses are not created in principle for their out of focus qualities, but rather their sharpness or contrast it's whatever happens. Aspherical lenses are designed to account for the differing refraction angles of colored light. While one may argue that this has some effect governing depth of field I'm sure the distances are so small that they would account for nothing.

5. SLRs and view cameras may let the photographer preview depth of field, but generally the stopping down of the iris leaves such little light that unless the conditions are right (very brightly lit) the photographer will see next to nothing of any usefullness.
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Old 08-01-2006   #21
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Mr Pythagoras, I did indeed visit your site, and very enjoyable it was, too, not least because Pythagoras is a hero of mine, and his theorem marks the beginning of all modern science, IMHO.

That out of the way, my approach to DOF - suck it and see! Yes I read the reviews, and I just bought a lens purely because of it's bokeh - the CZJ 180/2.8 Sonnar. And it's a gem.

But that said, I don't think about it beyond, what do I want to be sharp in this photo? As you pointed out, you can't really judge it except under a black cloth.

edit - ps I nearly always shoot at f2.8 if it's available. Faster lenses tend to get good at 2.8, and I've got used to the DOF of each lens at that aperture. If I want a picture to be 'sharp' I'll go down to 11 in bright light, but rarely below. But my 'home' aperture is 2.8

edit #2 - of course, when my head *is* under a black cloth, it's f32!
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Old 08-01-2006   #22
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Well, I guess DOF is misunderstood. The author of this post does not understand it either. DOF is not a sole product of angle of view. It is a product of magnification. Also, the final print size does not make much of a difference if viewed from the correct viewing distance as DOF is relative to the human visual system and does not have an absolute quality.
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Old 08-01-2006   #23
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Quote:
Originally Posted by Finder
Well, I guess DOF is misunderstood. The author of this post does not understand it either. DOF is not a sole product of angle of view. It is a product of magnification. Also, the final print size does not make much of a difference if viewed from the correct viewing distance as DOF is relative to the human visual system and does not have an absolute quality.
Whoa, Nelly! What does that mean?
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Old 08-02-2006   #24
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Quote:
Originally Posted by Sparrow
Perhaps I’m just not sophisticated enough, but what exactly is there to commend the OOF areas of that photo. No disrespect to the photographer, it is a legitimate subject.

Not sure there's anything special about that photo, but it does show how you can use depth of field to isolate the principle subject (the barb wire) from the background. In this case, the background is out of focus just enough - I can easily distinguish the barbed wire, and can see that it is the main subject - the photographer's choice of what is in focus signals that. At the same time, I can also see enough detail in the background to provide context and story, and that provides interest that would otherwise be lost if the background were extremely out of focus.

I don't worry an awful lot about this - I do use the depth of field scales on my lenses (I really miss that on digital/autofocus lenses). And I'm not averse to DOF bracketing - taking the same shot several times with a different f-stop/shutter combination to obtain different depths of field. I developed that approach back in my SLR days, and I never use the DOF-preview function that some SLRs allow.
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Old 08-02-2006   #25
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Quote:
Originally Posted by Oh Two
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4. Bokeh is a gift from God.
If He is in the lens-making business now, I don't think much of Leica's chances of survival......
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Old 08-02-2006   #26
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I think that Diety just guides our lenses. However, I wonder what that photography company would be named?
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Old 08-02-2006   #27
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all I know is their motto would be "Christ! That's a good lens!"
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Old 08-02-2006   #28
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LOL, thats funny!!
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Old 08-02-2006   #29
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Quote:
Originally Posted by rvaubel
Whoa, Nelly! What does that mean?
I believe people misunderstand DOF.

The author of the post has also misunderstood it. He thinks the sole criteria for DOF is angle/field of view. That is not true otherwise DOF would be the same for every format given the same field/angle of view and that is not so.

DOF is related to magnification. DOF is affected by three factors: aperture, object distance, and focal length. With a given aperture and a given magnification, DOF will be the same; notice focal length and object distance change to maintain magnification.

It does not matter whether the print size of the final image is known or not. If you view an image from the correct viewing distance, which is equal to the diagonal of the print, then the DOF will appear the same. Since effect of DOF is relative to the angular resolution of the human visual system, as long as the viewing distance is keeped to a constant ratio to print size, the DOF will appear the same regardless of the linear dimensions of the print.

Just like sharpness, DOF has no absolute quality. It can only be defined in terms of the human visual system and is therefore a relative quality. DOF will not be the same for a person with 20/10, 20/20, or 20/30 vision simply because the difference in angular resolution. DOF scales and tables are calculated based on average vision, but you can calculate it for above average or below average vision if you perfer.

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Old 08-02-2006   #30
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I think that Diety just guides our lenses. However, I wonder what that photography company would be named?
Lens made in Heaven and distributed by the Vatican
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Old 08-02-2006   #31
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Quote:
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If He is in the lens-making business now, I don't think much of Leica's chances of survival......
I thought He worked for Leica. At least that is what their customers seem to imply.
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Old 08-02-2006   #32
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Quote:
Originally Posted by Finder
I believe people misunderstand DOF.

The author of the post has also misunderstood it. He thinks the sole criteria for DOF is angle/field of view. That is not true otherwise DOF would be the same for every format given the same field/angle of view and that is not so.

DOF is related to magnification. DOF is affected by three factors: aperture, object distance, and focal length. With a given aperture and a given magnification, DOF will be the same; notice focal length and object distance change to maintain magnification.

It does not matter whether the print size of the final image is known or not. If you view an image from the correct viewing distance, which is equal to the diagonal of the print, then the DOF will appear the same. Since effect of DOF is relative to the angular resolution of the human visual system, as long as the viewing distance is keeped to a constant ratio to print size, the DOF will appear the same regardless of the linear dimensions of the print.

Just like sharpness, DOF has no absolute quality. It can only be defined in terms of the human visual system and is therefore a relative quality. DOF will not be the same for a person with 20/10, 20/20, or 20/30 vision simply because the difference in angular resolution. DOF scales and tables are calculated based on average vision, but you can calculate it for above average or below average vision if you perfer.

Better?
If you mean me, I think you missed part of the post. I stated "at a viewing distance of 75 cm". Your point about the angle of view (also in my post) as related to viewing distance and final print size is a nice clarification. And yes, wearing glasses changes the magnification with which one sees the world. Thank you.
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Old 08-02-2006   #33
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Imported into Italy from Vatican City, then exported from Italy so we'll be hit twice by import tax!? No thanks!
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Old 08-02-2006   #34
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could DOF be explained better if we call it "sharpness contrast" and use it just like we use brightness contrast or color contrast?
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Old 08-02-2006   #35
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Quote:
Originally Posted by ChrisN
Not sure there's anything special about that photo, but it does show how you can use depth of field to isolate the principle subject (the barb wire) from the background. In this case, the background is out of focus just enough - I can easily distinguish the barbed wire, and can see that it is the main subject - the photographer's choice of what is in focus signals that. At the same time, I can also see enough detail in the background to provide context and story, and that provides interest that would otherwise be lost if the background were extremely out of focus.

I don't worry an awful lot about this - I do use the depth of field scales on my lenses (I really miss that on digital/autofocus lenses). And I'm not averse to DOF bracketing - taking the same shot several times with a different f-stop/shutter combination to obtain different depths of field. I developed that approach back in my SLR days, and I never use the DOF-preview function that some SLRs allow.
Iím familiar with the technical cause of and the potential use of shallow DOF, and deep DOF for that matter. Itís the use of a value judgment that ďbokehĒ implies, and the concept that OOF areas can be rated in some way that I donít get!!
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Old 08-02-2006   #36
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Quote:
Originally Posted by jaapv
The symbolism of the barbed wire in focus in contrast to the normal-looking buildings, out of focus related to the history of that particular place. To me it condenses the whole story. Symbols are a personal thing, I suppose....
The photographers other images of the same subject have a stark brutality that fits the history of that place well; I would contend the softness in that one is less appropriate.
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Old 08-02-2006   #37
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Well, we agree the series as a whole is very good then, and clearly agree to disagree on the best one. That is as it should be.
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Old 08-02-2006   #38
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Quote:
Originally Posted by jaapv
[color="DeepSkyBlue"]
1. Without knowing the end enlargement of the photo one takes and without taking the contrast into consideration, judging the amount of DOF is actually rather hit and Ėmostly- miss.

3. Film is not without thickness. In reality a COC of 0.03 mm will act like a torch shining into a murky plate of soup. It will produce a cone, diffractions, reflections, if the light strikes the film at an angle it will turn into an oblong, etc., the net result being a larger diffuse spot.
Jaap,
i read this all with interest, not sure I got your message tho.

Ad 1:
The later enlargement factor is irrelevant at this point, and speaking of "hit and miss" considering the limitations of the human perception and the contrast issue, well, in which case could this get relevant in real life ? There is more risk of failing in misaligned RFs or flange tolerances I'd say. Not to speak of film flatness, especially at MF.

Ad 3:
I admit the "torch shining into a murky plate of soup" (!!) is really a brilliant illustration, but again, where is the relevance of this factor in practical photography ? Correct me if I am missing soemething here.

In the whole photographic process there is a bunch of technical limitations causing tolerances. But as long as they show no real impact on the practical result, we all dont care, don't we ?

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Old 08-02-2006   #39
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Human perception is okay up to a point, but it is not infallible, and that's why we have reason and physics.

The earth is not flat and does not ride on the back of a tortoise; despite our perception, the earth goes around the sun and not vice-versa; clean, white light is actually a mixture of all the colours of the spectrum; in quantum mechanics, a particle CAN be in two places at once; rays of light, when passing through a narrow circle, such as a 21mm lens diaphram at f/22 or f/32, are traveling on a nearly parallel path when striking a film plane approximatley 30mm away from the lens and so will not demonstrate any perceptible variance in sharpness between near and far objects.
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Old 08-02-2006   #40
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Quote:
Originally Posted by fitzihardwurshd
Jaap,
i read this all with interest, not sure I got your message tho.

Ad 1:
The later enlargement factor is irrelevant at this point, and speaking of "hit and miss" considering the limitations of the human perception and the contrast issue, well, in which case could this get relevant in real life ? There is more risk of failing in misaligned RFs or flange tolerances I'd say. Not to speak of film flatness, especially at MF.

Ad 3:
I admit the "torch shining into a murky plate of soup" (!!) is really a brilliant illustration, but again, where is the relevance of this factor in practical photography ? Correct me if I am missing soemething here.

In the whole photographic process there is a bunch of technical limitations causing tolerances. But as long as they show no real impact on the practical result, we all dont care, don't we ?

Regards,

Fitzi
Maybe it is just the way my mind works. Even if I don't need to know how or why something works in order to operate it, as is more and more common nowadays, I want to understand how and why it works nevertheless. It simply gives me more satisfaction, and it gives me the illusion of better results.
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