DOF and film format

Anyway, I am interested in this discussion because I am new to medium format and knowing these types of things would help me visualize the image while taking it. Understanding the differences ahead of time might help me take better photographs.


edited for caustic remarks...
 
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Here is a little experiment YOU ALL CAN DO -- no medium format required:

Shoot Frank's model in the marina with your favorite 50 on you 35mm camera (at say f4). Now shoot the same scene with your 105 (or 90 -- whatever telephoto you have) AGAIN on your 35mm camera, from the SAME spot/distance from your model. Focus both lenses the same. Of course the telephoto will cover less of the scene.

Now enlarge BOTH negatives so that the model's face is identical size on your print. Yes, the telephoto one will enlarge less as the model's face is larger in it.

Now look at the out of focus/background detail. Which to you like? Which to do find more 'out of focus'?

Points to remember:

1) The medium format coverage will cause the telephoto (105 or so) lens to render the entire scene -- much like the 50 on the 35mm.

2) A 105 is a 105 when it come to what is in focus. Format only affects coverage for a given lens length.

3) The face of the model will be of the same size (say in milimeters) in ALL format films as long as the lens used is the same length (say 100mm) and your distance from) the model is the same.
 
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Maybe someone already posted this DOF calculator:
http://www.dofmaster.com/dofjs.html

This calculator assumes you enlarge your negative (35mm, 6x6, 8x10, etc) to the same size of print (10 inches wide, if I'm not mistaken), with no cropping whatsoever.

If you want to crop your picture or enlarge it to something other than 10 inches... this calculator won't help you... you're on your own!
 
Obviously experience is the best way to learn anything, and it's a shame that my fuji acros 100 hasn't come in the mail yet because I wouldn't be here. I don't really see anyone getting bent out of shape maybe because everything I say is is light hearted and I just assume everything else is as well.

back on track, now someone tell me if I have this backwards. A greater enlargment = a smaller (perceived) sharp focus area?

in that case would a smaller negative result in less DOF because of the greater amount of enlargment?
 
Brennotdan said:
back on track, now someone tell me if I have this backwards. A greater enlargment = a smaller (perceived) sharp focus area?

in that case would a smaller negative result in less DOF because of the greater amount of enlargment?
Click to expand...
DOF calculations are non-linear (see here)
http://www.dofmaster.com/equations.html

So there isn't a simple rule-of-thumb that applies to all negative sizes and enlargment factors.
 
I will add a different thought, too.

Do you like how your telephoto (say 100mm) renters out of focus areas (for a given f-stop), and, do you wish you could include more scene around your subject when you look at your telephoto pictures?

If your answer is 'yes', then shoot medium format with the same size lens (say 100mm).

Do you like your telephoto (100mm) coverage on your 35mm, but wish it had more depth for a given f-stop? Use digital with a crop factor (Olympus has a 2x, so your 50mm will do the trick).
 
dnk512 said:
Here is a little experiment YOU ALL CAN DO -- no medium format required:

Shoot Frank's model in the marina with your favorite 50 on you 35mm camera (at say f4). Now shoot the same scene with your 105 (or 90 -- whatever telephoto you have) AGAIN on your 35mm camera, from the SAME spot/distance from your model. Focus both lenses the same. Of course the telephoto will cover less of the scene.

Now enlarge BOTH negatives so that the model's face is identical size on your print. Yes, the telephoto one will enlarge less as the model's face is larger in it.

Now look at the out of focus/background detail. Which to you like? Which to do find more 'out of focus'?

Points to remember:

1) The medium format coverage will cause the telephoto (105 or so) lens to render the entire scene -- much like the 50 on the 35mm.

2) A 105 is a 105 when it come to what is in focus. Format only affects coverage for a given lens length.

3) The face of the model will be of the same size (say in milimeters) in ALL format films as long as the lens used is the same length (say 100mm) and your distance from) the model is the same.
Click to expand...


Yes, that is correct (as far as I know.) 🙂
 
Brennotdan said:
wow.... digital sensors make people crazy.
Click to expand...

Yeh, I guess it does. I know I had a hard time remembering to shoot at wider aperatures than what I was used to with 35mm film cameras when I started to use an Olympus C5050 with it's very small sensor. Again just a different format and being a much smaller size than 35 it had , to me, more apparent DOF at any given f stop. Digital being what it is was cheap to find out what the difference was unlike med format which is expensive to experiment with.

Bob
 
Sharpness is a complicated subject, but DOF less so. It really is just a calculable value--with certain subjective assumptions to be sure, regarding "normal" print sizes and "normal" human vision, incorporated into the value used for acceptable CoC--but there really isn't any need to get worked up over this topic.

DOF is always calculated relative to focal length, aperture, subject distance, and format, based on print sharpness, so enlargement factor is included in the calculation. Format is expressed in the calculation by the value chosen for the acceptable circle of confusion.

Experience and taste come in when you consider whether or not to accept the standard DOF value when you decide what aperture to shoot at. Say you plan to make a very big enlargement--if you're the sort of person who calculates these things, you might use a smaller value for acceptable CoC than what is normal for the format. If you just use the DOF scale engraved on the lens, you might decide to stop down one or two more stops than the scale recommends, and you would be doing the same thing.

For those who want to try running some numbers and reading about the formulas used to calculate those numbers, I recommend a shareware program called "f/calc." The formulas used by the software are in the help screens, and they are explained more clearly there than I could do here.
 
There is those who feel photography is an art and those who feel it is a philosophy and then there is those who see and understand the simple physics in it. An understanding of DOF, nevertheless, should be important for all three types, and users of whatever format there is. I was surprised to read a forum member state that the M8 simply "crops" the final image and that the DOF markings on the lens barrel do not change.
 
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