DOF and Cropping take 2

Started 10 months ago | Discussions thread
moving_comfort
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Re: DOF and Cropping take 2
In reply to awaldram, 10 months ago

awaldram wrote:

Let break it down even further

DoF and Focal Length is an inverse Quadratic.

As you increase focal length so magnification increased therefore fairly obvious as we know the entry pupil is as viewed through the front of the lens that if we double focal length then for the same F number the physical aperture is doubled.

So for the same F number at the same Magnification you have the same DoF.

so if you shoot 50mm f2.8 at 10ft then walk 40ft away and shoot the same target with 200 F2.8 then DoF and image will be identical.

I suggest you read

http://groups.csail.mit.edu/graphics/classes/CompPhoto06/html/lecturenotes/22_DepthDefocus_6.pdf

which is the lecture notes for courses 6.098 (Digital and computational Photography) and 6.882 (Advanced Computational Photography) MIT-EECs

or are you now going to say

Cambridge in colour are wrong

Luminous Landscapes are wrong

I'm wrong James is wrong and the Massachusetts Institute of Technology is wrong as well !!

Do you not think maybe they are not ?

I think the problem here is that you're throwing some good information in with the bad in order to support something you were saying earlier.  The appearance of the 'good' information does not suport all your previous statements, because the 'good' information is in conflict with them.

Let's summarize, try to be succinct so we can know the point you're trying to make:

Q:  Does cropping FF (to ap-sc, for example) change DOF when displayed at the same sizes?  Because I think you used to hold the position that it does not.**

** I'm referring to, for example, this post where you seemed to be getting it wrong

.

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