What is the biggest, perfectly sharp format you can get from your sharpest negatives?

Diapositivo said:

Ahem, yes, that seems sharp enough :w00t:

Is this 135? Something like Kodak Technical pan? With a very good lens (which lens?).

Fabrizio

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Yes, Leica M3 with Dual Range Summicron in close mode. I haven't been able to turn up the negative to say for sure what the film was, but some ordinary Kodak film from around 1980 (PX or TX).

RalphLambrecht said:

Equal magnification, yes, equal DoF, no.

Enlarging a negative changes final print resolution but not the depth of field, which is already locked into the negative.

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Is not.

All the negative contains are blobs of silver of various size, corresponding (hopefully) to the blobs of light the lens projected on the film.
DoF is not fixed at this point at all: don't enlarge the negative at all, and every blob below the angular resolution limit of our eyes will not be seen as a blob.
With increasing degree of magnification, blobs begin to be discernible as blobs, i.e. unsharp.

Only when you have reached the point that continued enlarging will no longer enlarge blobs previously too small to be recognized as blobs will DoF no longer change.

(By that time, the entire print will look unsharp.
Which is (as i wrote earlier) something that could be explained as having a very large DoF.
)

So unless you assume you hve teased out everything there is in a negative, enlarging it will reduce DoF.

RalphLambrecht said:

A brief look at the DoF equation shows that, aperture and subject distance being equal, focal length and CoC are the controlling factors. The CoC difference between formats is compensating for by the different magnification needs, but the focal length advantage of shorter lenses remains.

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Focal length is only a factor in DoF in as far as it, combined with distance, sets magnification.
And that's what you are saying too: there are three factors that determine DoF. Aperture, the CoC criterion, and Magnification.
I agree with that 100%.

So don't throw out magnification when it comes to print sizes. Every time you enlarge a negative, you are changing magnification. And with it DoF.
Just as every time you take a closer look at a print, you're changing magnification, and DoF as well.

Q.G. said:

... Every time you enlarge a negative, you are changing magnification. And with it DoF. ...

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Sorry, but you cannot change DoF after the exposure. Take a look at the equations for front and rear DoF. The factors controlling DoF are subject distance (u), circle of confusion (c), and aperture (N) and focal length (f) of the taking lens. None of these factors can be changed after the exposure. DoF is locked into the negative.

You can change the resolution of it, but not the DEPTH of field.

I usually don't go above 11x14, and for most part it is quite good.

Jeff

RalphLambrecht said:

Sorry, but you cannot change DoF after the exposure. Take a look at the equations for front and rear DoF. The factors controlling DoF are subject distance (u), circle of confusion (c), and aperture (N) and focal length (f) of the taking lens. None of these factors can be changed after the exposure. DoF is locked into the negative.

You can change the resolution of it, but not the DEPTH of field.

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Yes, you CAN.

Just like changing viewing distance does.
Or will you now also claim that CoC criteria do not contain assumptions about viewing distances?

If viewing distance can change DoF (or invalidate CoC criteria), i.e. if magnification can change DoF, why would uhm... magnification not be able to change DoF?
It, of course, can and does. It cannot not do that.


I'm a bit disappointed, Ralph, that, after your very correct explanation of the few things that are involved in DoF, you now come up with these omnipresent perverted Hyperfocal distance (!) formulae.
Can you explain why focal lengths now is taken into account, not once, but several times?
Together with distance, it forms magnification. But why would it feature again? What does it represent then?

But there i go again. I had promised myself never to busy myself with mystical calculations of an inherently incalculable entity.
So i won't.

We don't have to. After all, the question above, about CoC and viewing distance suffices.

Q.G. said:

Yes, you CAN. ...

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No, I cannot change the math.

Q.G. said:

... Or will you now also claim that CoC criteria do not contain assumptions about viewing distances? ...

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Oh no, CoC contains the assumption of proportional viewing distances. I always said that.

Q.G. said:

... If viewing distance can change DoF (or invalidate CoC criteria), i.e. if magnification can change DoF, why would uhm... magnification not be able to change DoF? ...

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Viewing distance cannot change DoF.
Viewing distance does not invalidate CoC.
Print magnification cannot change DoF.

Q.G. said:

... Together with distance, it (focal length) forms magnification. ...

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Yes, subject magnification on the negative, and subject magnification on the negative does change DoF, but print magnification does not.

Your statement was:

But enlarge both to the same size print, and you will have not only achieved equal magnification, but also equal DoF.

That is not correct, as any comparison of two prints made from negatives taken with different focal lengths, but enlarged to the same subject magnification on the print, will easily show. The photographic literature is full of examples.

Sorry to have disappointed you.

holmburgers said:

The pixel analogy can just as easily be applied to analog....

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JBrunner said:

I beg to differ...

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Perhaps easily is not the right word. The point is, there are actual limits to our perception of 'separation' between a black & white point. At some point it becomes 1, gray, point.

I think the word pixel is what's causing dissension here; but the original point refers to the limits of our eye and nothing more.

Certainly though, there are other effects on perceived sharpness besides just resolution, but the kinda of un-ending detail that I think we are all referring to comes down to minimal enlargment, fine grain (which every modern film meets, save maybe for 3200), and that requires larger format, and someone in my presence is more than welcome to use the concept of pixels if that helps them understand this fact.

A pixel is just an element of information, and there are analogous measurements in an analog photograph.

Definition: Circle of Confusion, noun, "A group of photographers sitting around discussing depth of field."

Allen Friday said:

Definition: Circle of Confusion, noun, "A group of photographers sitting around discussing depth of field."

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I needed that. Cracked me up. Thanks!

RalphLambrecht said:

No, I cannot change the math.

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Never mind. It's all invalid anyway.

RalphLambrecht said:

Oh no, CoC contains the assumption of proportional viewing distances. I always said that.

[...]

Viewing distance cannot change DoF.
Viewing distance does not invalidate CoC.
Print magnification cannot change DoF.

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And that's where you're completely wrong.

Why, do you think, does the criterion for acceptable CoC size contain an assumption about viewing size?

Why do you think that, despite that, viewing distance cannot change DoF?
It of course can, and does.
That's why they put that into the criterion.

If viewinfg distance cannot invalidate DoF, there's no need to put an assumption about viewing distances in the criterion for DoF.
So again, why would you say did they do that anyway?

Why would viewing distance matter enough to make it an integral pat of the CoC/DoF criterion, but print size not?
You cannot separate the two.

So yes: print magnification, any (!) magnification, changes DoF.

I'm sure you think that looking at prints will easily show you are right.
But once you figured out how things work, once you have found the answer to the above questions, you will see that all that was easily done is fool you into believing that you could easily see what you thought you could easily see.


Print magnification does indeed change DoF. It cannot not do that.

Q.G. said:

... And that's where you're completely wrong. ...

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Good grief...

Q.G. said:

... Print magnification does indeed change DoF. It cannot not do that.

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Just repeating this nonsense doesn't make it right, you know. Why don't you try your own print example and see how two focal lengths will produce a different DoF despite having the same subject magnification on the print?

Alternatively, I can scan an example and show you?

Allen Friday said:

Definition: Circle of Confusion, noun, "A group of photographers sitting around discussing depth of field."

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Allen

You are absolutely right. I really don't know why I put myself through this pain sometimes. I should know better.

RalphLambrecht said:

Good grief...

Just repeating this nonsense doesn't make it right, you know.

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You read my mind, Ralph.

Can't help but notice that you have not even tried to remove the obvious contradictions in what you wrote. And i don't need to hear how you solve that. I'll just leave you to think about it.

When I was young I bought a book in which this consideration was made.

We take a picture of a heron. We use 135 film, and 200mm focal lenght. The heron fills the picture.

We take the same picture of the same heron. Same point of view. We use 120 film, and we use a 200mm lens on our Hasselblad. The heron will not fill the picture.

We now have two negatives. The 120 and the 135.

We print the 135, this print of X size has a typical "tele" perspective effect and DoF.
We print the 120, this print of the same X size has a less pronounced "tele" perspective effect, and seems to have more DoF. The heron does not fill the frame, we see water and vegetation around it.
We then print a 24x36 mm section of the 120 negative. We obtain a print of the same X size which is identical to the print from 135, identical also as far as perspective rendering and DoF are concerned.

That is because the focal lenght 200mm is what defines DoF and perspective appearance given equal magnification.

When printing the 120 the impression is that there is more DoF and that there is a different perspective rendering because the magnification was smaller. By enlarging more the 120 film, and bringing to the same level of enlargement to which we had brought the 135 image, we see that the DoF and the perspective effect coincide.

I suppose this in accordance with what Q.G. says.

DoF is defined as a function of the CoC which is defined as a function of magnification. The "depth of field scale" that is printed on lens barrels is the typical acceptable DoF when printing in small formats. It is somehow known that when printing larger, as usual vision is going to be, in comparison, nearer (we don't see large prints at a distance equal to its diagonal, we tend to see large prints from a comparatively shorter distance than small prints, and normally there is no piano to avoid that) then we cannot rely on the depth of field scale printed on the barrel. We would use the DoF scale for 8 when we use f/11 (corrected).

That is, again, to confirm that DoF depends from magnification. When we see the print from nearer, we "magnify" it. The CoC that, measured on film, was acceptable on a negative printed small is not any more acceptable on a negative printed large and seen from comparatively nearer. The DoF on the negative is not valid in abstract but it depends on how much we are enlarging it, or on how much we are enlarging all those CoC.

Besides the page on CambridgeinColour already mentioned, a further photographic enquiry into the matter is performed here:

http://www.luminous-landscape.com/tutorials/dof2.shtml

The question is very interesting, as everything which is counter-intuitive. Let's avoid any bickering though

Fabrizio

PS The book in question is "La Caccia Fotografica" by Gandolfi. In a kind of photography in which long focal lenses are required and DoF is never enough, a photographer might be tempted to think that using a small format he is advantaged because he reaches a higher magnification. He is not. The magnification is the same. You can always enlarge a smaller portion of your larger film.

In modern digital times, people say that 4:3 format is better for nature photography because you can have an equivalent 400mm with the size of a 200mm. That's wrong. If you use a 200mm on a FF digital camera, and only print the part of the frame corresponding to the 4:3 format, you would get an "equivalent" 400mm anyway.

RalphLambrecht said:

Allen

You are absolutely right. I really don't know why I put myself through this pain sometimes. I should know better.

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Ralph:

See (there was a url link here which no longer exists)

Ralph's definition of depth of field embeds viewing distance (diagonal of the print). I find it convenient, clear and acceptable because it is easily explained and repeatable.

But always willing to question the relevance of standards to ourselves, I propose we define a new term.

Personal Depth of Field (PDoF).

PDoF is what you get when you calculate DoF using your personal viewing distance.


As Diapositivo suggested you might start PDoF at one or two stops lower than standard. For example, line up infinity with f/11 mark and set aperture to f/16.

But you have to do extensive testing to get real PDoF.

Q.G. said:

... I'll just leave you to think about it.

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No need to be patronizing. After presenting the math for my argument and offering pictorial evidence, you may want to put your cards on the table. Show us the math that shows how print magnification changes the DoF. I'm really interested.

RalphLambrecht said:

No need to be patronizing. After presenting the math for my argument and offering pictorial evidence, you may want to put your cards on the table. Show us the math that shows how print magnification changes the DoF. I'm really interested.

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No need for maths either:

Bill Burk said:

Ralph's definition of depth of field embeds viewing distance (diagonal of the print). [...]

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Why?
There's your (!) answer.

Q.G. said:

No need for maths either:



Why?
There's your (!) answer.

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Still waiting for your evidence? Show me the math.

RalphLambrecht said:

Still waiting for your evidence? Show me the math.

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Stubborn you are.

You are not going to get maths. I have told you that. I have told you why too.

We also do not need maths.
I mentioned the contradictions in your reasoning earlier.
Just understand (no math needed. No explanation either; i do know how it works) why you included print size in your own definition, but don't allow for print size when someone else suggests it.

Q.G. said:

Stubborn you are.

You are not going to get maths. I have told you that. I have told you why too.

We also do not need maths.
I mentioned the contradictions in your reasoning earlier.
Just understand (no math needed. No explanation either; i do know how it works) why you included print size in your own definition, but don't allow for print size when someone else suggests it.

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Q.G.

You have no evidence, I get it. Just twisting words and hiding behind rhetoric. Come back when you can show some data or pictorial evidence.

RalphLambrecht said:

Q.G.

You have no evidence, I get it. Just twisting words and hiding behind rhetoric. Come back when you can show some data or pictorial evidence.

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This is Way Beyond Silly, Ralph.

Where's the rhetoric in pointing out that you yourself say that print size matters, yet do not allow that print size matters when someone else - me, in this instance - says it?
Pointing out the Bleeding Obvious is twisting words?
Come on! I know you are better than this!

So here we go again. Maieutics then. Step 1.
Why do you say, Ralph, that viewing distance and print size matter when DoF is concerned?

Q.G.

Still waiting for your evidence. Math, data, pictorial samples. Where is it?

My claim: DoF is locked in after exposure. Print magnification cannot change it.
My proof: All published DoF equations include nothing but image-taking parameters.

Your claim: DoF can be changed with print magnification.
Your proof: ?

How? Just tell us. Really like to see it.

RalphLambrecht said:

No need to be patronizing. After presenting the math for my argument and offering pictorial evidence, you may want to put your cards on the table. Show us the math that shows how print magnification changes the DoF. I'm really interested.

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Dear Ralph, dear Q. G.,

I don´t want to intermediate, but it seems that you both misunderstand each other...Try to resolve this.


My interpretation or maybe another point of view on DoF and enlargement factors:

You can skip this digging through some DoF calculation examples if you want. The important result is at the bottom.

What counts is the result. Let´s assume you have a 35 mm cam with a 42mm lens and a 5x7 inch cam with a 210mm lens located at the same point and you want to shoot (again) an object that is distanced 5 meters and something before and behind the 5 meters in the DoF. The framing of the scenery in both negatives is the same. After shooting I want to make a print, lets say in the size of 15x21 inch. I assume that a print must have 7 lpm to become reasonable sharp. Then I need at least 21 lpm in the 5x7 inch negative (3 times linear enlargment) and at least about 105 lpm in the 35mm negative (around 15 times enlargement).

I want to shoot at f/22 with the 5x7 inch. With 21 lpm the CoC is about 0,05 mm. The resulting DoF is from 4,47 m to 5,68.

Now the important thing in my example. To have a realistic chance to get 105 lpm with 35 mm I can not shoot at f/22 due to the diffraction limit of around 70 lpm. I must open the aperture at least to f/11 where the diff limit is about 150 lpm. Therefore for the 35 mm camera DoF I have to calculate with an aperture f/11 and a CoC of about 0,01 mm (for the 105 lpm). The resulting DoF is from 3,82 meter to 7,24 meter. Still more DoF with 35mm than with 5x7 inch but not as much as one would expect, if you could calculate with the same CoC and the same aperture and only the focal length would differ.

But I can find theoretical examples where the 35 mm cam with a 42 mm lens DoF and the 5x7 inch cam with 210 mm lens DoF that are needed for the same sharp print nearly become equal due to the different magnification needed for the same size and the same sharp print and the diffraction limits of different apertures.

Maybe you want to have a 25x35 inch print from both formats (very hypothetical!). You would need 35 lpm in the 5x7 inch negative for that end format to get sharp. For the 35 mm negative 175 lpm would be needed. With 5x7 you could again shoot at f22 to make the 35 lpm. But due to the diffraction limits with the 35 mm camera you have to use f/8 (or even f/5.6) to have at least a theoretical chance to make the 175 lines. I hope you can see what I want to say although this is all very theoretical and hypothetical. You had now to compare the DoF of a 210 mm lens at f 22 with a CoC of 0,03 mm (35 lpm) and the DoF of a 42 mm at f/8 (or even only f/5.6) and a CoC of 0,005 mm (175 lpm).

So DoF calculations are surely indirect dependent on the enlargement factor or the print format you aim at. Because the resulting maximum CoC that is allowed for sharp pictures and that is directly in the DoF formula changes with different negative formats if you want to enlarge them to the same size and same sharp print.

Now all are confused. Still hope to help resolving your misunderstanding...

Best,
Andreas

Ralph, if I can answer this otherwise two-sided argument, I would like to refer to the very well explained text of Cambridge in Colour to which I have often referred.

It says, among other:

When does the circle of confusion become perceptible to our eyes? An acceptably sharp circle of confusion is loosely defined as one which would go unnoticed when enlarged to a standard 8x10 inch print, and observed from a standard viewing distance of about 1 foot.
At this viewing distance and print size, camera manufactures assume a circle of confusion is negligible if no larger than 0.01 inches (when enlarged). As a result, camera manufacturers use the 0.01 inch standard when providing lens depth of field markers (shown below for f/22 on a 50mm lens). In reality, a person with 20-20 vision or better can distinguish features 1/3 this size or smaller, and so the circle of confusion has to be even smaller than this to achieve acceptable sharpness throughout.
A different maximum circle of confusion also applies for each print size and viewing distance combination.
(bold mine).

You say, if I get you right, that the DoF is "locked" into the negative, as the enlargement is supposed to be made in a way that the larger the enlargement, the larger the viewing distance, so that enlarging is out of the equation and in fact in the equation you give "enlarging" does not seem to take part.

But in the course of this discussion, the point that raised the divergence between you and Q.G. was, on post #76, that by enlarging "more" a portion of a certain negative one ends up with the same DoF that he would have had by shooting that portion of negative "straight away" (shooting with a smaller format). Your point being that smaller formats have more DoF and the point by Q.G. and by me being that the more you enlarge the smaller negative the less you have DoF so DoF is depending on enlargement.

In this context, what Q.G and I are saying is that you enlarge your negative more than the standard reference points which people take as "given" and keep as constant when they write those equations that you quote.

In the text that I quoted above, reference is made to the enlargement as it is, in fact, one of the things to be taken into account when we consider comparisons among formats.

Reading again the thread, I would also like to express my point again regarding your affirmation in post #72, and then by hpulley in post #73, to which both I peacefully disagree.

The point some of us were raising in this thread it is that micro formats are NOT kissed by a larger DoF even if it seems so given to our habit to compare different magnifications (equal final prints of different sized negatives).

If you compare equal magnifications of the negatives, micro formats don't have any more DoF than "macro" formats.

To explain this strange proposition, consider this:

you go round with two cameras: one is a 135film camera, and the other is a film camera that has the film surface of the 4:3 standard :wizard:

You take the same scene with a 25mm on both cameras. The area covered by the full frame of the 135 will be "wide-angle". The area covered by the 4:3 film camera will be "normal". So the two scenes will differ in your viewfinders.

When at home, if you print only the portion of the 135 corresponding to the 4:3, you will have the same image, same perspective, and importantly same DoF that you obtain when you print the entire 4:3 frame.

That would be "equal magnification", because you enlarge your negative the same "number of times" in both prints.

If, instead, you print the two images "full frame", you will have a different magnification, because you will have enlarged the 135 less than the 4:3.

In this second case, the print you make of the 135 full frame is enlarged "less" than the other, hence the higher apparent DoF. "Apparent" you will object. I see that DoF clearly being there. Yes. It's there, because the negative is less enlarged and the CoC less apparent. So it's there, but it is a result of the lesser magnification of the negative.

I don't know if I made my point clear. I hope we can discuss this very interesting technical topic without it becoming a competition about who's got it longer

Fabrizio