What about DOF

[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]

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]

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]

.

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......

 

[Stephanie Brim]

I think that Diety just guides our lenses. However, I wonder what that photography company would be named? 😀

 

[Ash]

all I know is their motto would be "Christ! That's a good lens!"

 

[Nachkebia]

LOL, thats funny!! 🙂

 

[Finder]

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.

Better?

 

[jaapv]

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 😉

 

[Finder]

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.

 

[jaapv]

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.

 

[Ash]

Lens made in Heaven and distributed by the Vatican 😉

Imported into Italy from Vatican City, then exported from Italy so we'll be hit twice by import tax!? No thanks!

 

[vicmortelmans]

could DOF be explained better if we call it "sharpness contrast" and use it just like we use brightness contrast or color contrast?

 

[Sparrow]

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.

I’m familiar with the technical cause of and the potential use of shallow DOF, and deep DOF for that matter. It’s the use of a value judgment that “bokeh” implies, and the concept that OOF areas can be rated in some way that I don’t get!!

 

[Sparrow]

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.

 

[jaapv]

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.🙂

 

[fitzihardwurshd]

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.

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 ?

Regards,

Fitzi

 

[VinceC]

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.

 

[jaapv]

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.