DOF and film format

[FrankS]

This issue came up a while ago and has not been answered definitively, so I ask for your help:

Consider a normal 50mm lens in 135 format at f3.5 focused at 5ft, and a normal 100m lens in 6x7cm format also at f3.5 and focused at 5ft.

The subject is a beautiful model 5ft from the camera and there is a marina behind her with lots of sailboat masts that will demonstrate out of focus areas.

The negs from each set-up will be enlarged to 11x16 inches for evaluation. (That means that the smaller neg will be enlarged to a greater degree.) Enlargement will be done with an optical enlarger to bypass digital scanning and printing issues.

Does one get greater DOF with a smaller film format than with a larger format, or is the effect of greater DOF with wider lenses nullified due to the greater degree of enlargement necessary to achieve the same sized print?

Will the out of focus sailboat masts behind the subject be rendered with the same degree of "out of focus-ness" in each 11x16inch print, or will the smaller format have less "out of focus-ness" and the larger format have more "out of focus-ness" in each 11x16inch print?

Just interested in putting this to rest in my mind.

This principle will be applicable to digital sensors, cropped vs. full frame.

 

[Nikon Bob]

That is an interesting question and I am also interested in the answer not having much experience with med format. I am going to guess that the 35mm neg having to be enlarged more will pretty much nullify any DOF differences in formats.

Bob

 

[David Goldfarb]

The smaller format will have more DOF, but you might like the medium format image for other reasons (less grain, better microcontrast, smoother out of focus areas, sharper sharp areas, etc.).

 

[FrankS]

The smaller format will have more DOF, but you might like the medium format image for other reasons (less grain, better microcontrast, smoother out of focus areas, sharper sharp areas, etc.).

Thanks David, I agree on both counts!

Ned?

 

[Roger Hicks]

The shorter focal length has more depth of field at a given focused distance and aperture. At least, so I have always been told, and always believed; and my belief is born out by experience. I have been assured by a physicist who should know that the advantage is lost on enlargement but on the basis of more than 40 years' experience, I do not believe him.

Of course the degree of out-of-focus-ness is governed by lens design and aperture position as well, so unless you are using (say) Tessars of identical geometry, scaled up or down as needed, this will make a difference too.

Cheers,

R.

 

[FrankS]

Fred, like Roger, I have seen this difference in DOF in my photography with different formats and in doing my own printing. The recent discussion of this topic in other threads had me wondering/doubting myself. That discussion was all a muddle, and I just wanted to clearly state the conditions so that this issue could be clearly resolved.

BTW, bokeh is not that difficult a concept either. Just look at the Summarit thread to clearly see examples of a very distinct character of bokeh.

 

[ferider]

The 50@f3.5 (35mm) has about twice the DOF as the 100@f3.5 (6x7), for 5ft focus distance and same final print size.

Thanks David, I agree on both counts!

Ned?

So if you know, why do you ask, Frank ? Trolling in my book; go RFF ...

 

[FrankS]

The 50@f3.5 (35mm) has about twice the DOF as the 100@f3.5 (6x7), for 5ft focus distance and same final print size.



So if you know, why do you ask, Frank ? Trolling in my book; go RFF ...

Trolling? Come on. I am a seeker of truth and clarity. I have seen this difference in DOF in my photography with different formats and in doing my own printing. The recent discussion of this topic in other threads had me wondering/doubting my understanding of this issue and the effect of greater enlargement of the smaller format. That discussion was all a muddle, and I just wanted to clearly state the conditions so that this issue could be definitively resolved.

 

[Tuolumne]

Has anyone done the exact experiment that Frank suggests? Could someone post the results for us to see with our own eyes?

/T

 

[aad]

Curious-isn't the depth of field of a given lens dependent on its focal length? If I crop a 6x6 negative down to 35mm format, how will it have changed the depth of field? Is it a product of proportionality?

An expensive test for film-maybe look at 2 lenses with the same focal length/different formats, see what the DOF scale says.

 

[FrankS]

I realize that this was a contentious topic, but that was the fault of the participants letting their egos and anger into the discussion. I'm just really wondering, and am hoping for a scientific analysis of the physics to support my observations. Roger mentined a physicist who argued against his observations. I thought it was an interesting topic. Isn't it a physics question rather than a subjective one, like perfect art?

 

[Tuolumne]

I realize that this was a contentious topic, but that was the fault of the participants letting their egos and anger into the discussion. I'm just really wondering, and am hoping for a scientific analysis of the physics to support my observations. Roger mentined a physicist who argued against his observations. I thought it was an interesting topic. Isn't it a physics question rather than a subjective one, like perfect art?

It seems like their should be an optical formula that expresses this exactly. Is there not?

/T

 

[FrankS]

T, I think the issue of contention is the effect of the greater degree of enlargement of the smaller format, which causes circles of confusion, small enough to be perceived as sharp points at a lower degree of enlargement, to become enlarged to a degree that they are now perceived as out of focus, resulting in less DOF, perhaps matching the DOF of the longer lens in the larger format.

That is the counter argument.

See Fred, we can talk about this.

 

[Solinar]

I shoot both 35mm and 6x9 film. The DOF penalty in using the larger film size is not trivial.

To get similar DOF results using Frank's comparison with the subject @ 5 feet from both cameras and the 35mm frame exposed at f/2.8 - a 6x9 shooter would need to use a lens with twice the focal length - then expose at f/5.6.

Now enlarge both negs to 11 by 14 and compare.

 

[Tuolumne]

The wikipedia Oracle speaks

The wikipedia Oracle speaks

Since we are on the Web, I have consulted the Oracle at Wikipeida, and here is what she said:


"DOF vs. format size

To a first approximation, DOF is inversely proportional to format size. More precisely, if photographs with the same final-image size are taken in two different camera formats at the same subject distance with the same field of view and f-number, the DOF is, to a first approximation, inversely proportional to the format size. Strictly speaking, this is true only when the subject distance is large in comparison with the focal length and small in comparison with the hyperfocal distance, for both formats, but it nonetheless is generally useful for comparing results obtained from different formats. To maintain the same field of view, the lens focal lengths must be in proportion to the format sizes. Assuming, for purposes of comparison, that the 4×5 format is four times the size of 35 mm format, if a 4×5 camera used a 300 mm lens, a 35 mm camera would need a 75 mm lens for the same field of view. For the same f-number, the image made with the 35 mm camera would have four times the DOF of the image made with the 4×5 camera."



For those who want to run the formulae, be my guest:
http://en.wikipedia.org/wiki/Depth_of_field



/T

 

[kuzano]

I haven't the slightest idea.....

I haven't the slightest idea.....

I have an 8X10 picture of a white Dahlia on a black background. The picture was taken in a Dahlia garden in bright daylight. The DOF is incredibly short. I have no idea how I got a black background in the image, nor how the short depth of field was acheived. It is one of my favorite close up pictures, yet if asked to duplicate it, I would be lost.

Perhaps one of the things that makes it a favorite is the mystery that surrounds the acquisition of the image.

I took the picture with some nondescript Autofocus SLR (probably a Pentax). The camera most likely had a short zoom lens attached. The camera was most likely set on either A or P, and the zoom was more than likely set at the widest angle.

I do not recall any of the other technical data, as I was far more interested in scoring points with the lady who accompanied me to the Dahlia Gardens. I do know that the Dahlia Gardens were in Canby Oregon, West of the town, toward Interstate 5.

I saw the last thread on this subject and have made every effort not to invoke anger in anyone with my tecnical details.

Does this help you with your question in any way?

 

[kuzano]

Physics is a theoretical science

Physics is a theoretical science

I realize that this was a contentious topic, but that was the fault of the participants letting their egos and anger into the discussion. I'm just really wondering, and am hoping for a scientific analysis of the physics to support my observations. Roger mentined a physicist who argued against his observations. I thought it was an interesting topic. Isn't it a physics question rather than a subjective one, like perfect art?

My long held conclusion, as an engineering student many years ago, is that the theories expounded by physicists are vague and meaningless in the real world and that Physicists are no fun at parties unless introduced to hallucinogenics of one sort or another. Some years ago, I spend three days with a physicist one evening.

 

[FrankS]

My long held conclusion, as an engineering student many years ago, is that the theories expounded by physicists are vague and meaningless in the real world and that Physicists are no fun at parties unless introduced to hallucinogenics of one sort or another. Some years ago, I spend three days with a physicist one evening.

That must have been an interesting week. 🙂

 

[Tuolumne]

Fred,
I must have missed the earlier thread on this topic, so I don't know what all the anger is about. It seems like a pretty straightforward question, and one I have wondered about myself from time to time. It's great to have one's intellectual curiosity satisifed, whether it's useful for anything else is moot. So, I'm happy that I found out something I had been wondering about, and can now move on to ther things. I think this thread is now closed for me! 🙂

/T

 

[Nikon Bob]

I know nobody wants to go there but I will. I took a photo of a building that I thought might make a good enlargement. It was a disappointment because at the aperture that I had used there was not enough apparent DOF in the enlargement to hold the building front to back in acceptable sharpness. It did look fine at 4x6 though. I am taking it that enlarging an image can have an effect on what I see as apparent depth of acceptable sharpness. That is why I thought FrankS had an interesting question in the first place. I can't understand why anyone would get bent out of shape discussing it. As T says it might help me get a better understanding of a new format before I use it.

Bob