What about DOF

[jaapv]

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 1920íes.
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

[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.

[rover]

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

[Nachkebia]

I have no problem with DOF on rangefinder, I was SLR shooter for long time and I can imagine

[VinceC]

>>I know, lots to read<<

But worth the effort.

[VinceC]

>>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.

[Ash]

ok I got halfway through that and it all went WAY over my head

[jaapv]

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.

[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.

[tetrisattack]

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!

[Sparrow]

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!!!

[Ash]

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

[John]

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?

[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

[Sparrow]

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 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.

[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....

[laptoprob]

Originally Posted by Ash

The sun goes up, you take a photo. The sun goes down, you party

What more is there to life?

[telenous]

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).

[Ash]

Originally Posted by laptoprob

What more is there to life?

Other than longboarding and girls? Nothing I wanna know about

[Oh Two]

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.

[pfogle]

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!

[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.

[rvaubel]

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?

[ChrisN]

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.

[jaapv]

Originally Posted by Oh Two

.

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......