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# Thread: DOF - OK, I'm confused!

1. I did that and I know what it does.... I'm trying to make sense out of it and understand what I see. Thanks though.

2. Fair enough.

3. Originally Posted by fdisilvestro
It's not the physical size of the aperture that goes into that calculation but the entrance pupil - the aperture as you see it when you look through the lens from the front.

Yes, that is correct. I should have been more specific.
That's why it is so cumbersome to work with actual apertures. They are not easily determined. Working with f/stops is a lot simpler, in my opinion.

Originally Posted by fdisilvestro
If you shot both film formats with the same lens at the same aperture, you would have identical depth of field in both frames.

No, since the CoC are not the same.
Correct, if both film formats are enlarged to the same print size, the smaller format will have less DoF with the same focal length and f/stop, because it was enlarged more. Remember, we are always assuming the same print viewing distance.

Originally Posted by fdisilvestro
... In this case the AOV is not the same either.
Correct. The angle of view (a) is given by the equation below:

a = 2*arctan(d/2*f)

where ‘d’ is the dimension of the negative-format diagonal and ‘f’ is the focal length.

4. Originally Posted by Tom Nutter
I think the real solution is to take out the gear you have and shoot pictures and look at your results. Experience will tell you what aperture to pick.
I am always mildly amused by these lengthy technical discussions.
I'm glad you're entertained and still hanging in there. I always learn something during these lengthy technical discussions. Not just talking about it, and going out there and do it, is important. But, knowing what to do when out there also helps.

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