Misconceptions about DOF, lens brightness, etc.

Started Feb 10, 2012 | Discussions thread
skrulm8
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Re: Misconceptions about DOF, lens brightness, etc.
In reply to sherwoodpete, Feb 10, 2012

I think your answers are misleading because they rely on obscure technical details of how we've come define the DOF.

See, the reason why the values of the DOF change between the same lens on a 7D and a 5D II is because the pixel denisty has changed, and the DOF was defined in relation to pixel denisty. If we were looking at prints from both these cameras where the print resolution exceeds the resolution of the eye at that distance, the DOF, of course, would look to us exactly the same way. And, yes, relative to the resolution of our eye (which is what actually matters), they would have exactly the same DOF, not merely appear so.

So, if I were to take the 5D II and crop its sensor to APS-C size, the DOF calculator would rightly show that the DOF results for the same lens remain unchanged. Also, if I were to take the ASP-C sensor in the 7D and expand it to the size of 35 mm film, the same lens would obviously give the exact same DOF on both cameras. No amount of cropping or magnification anywhere would change anything.

The absurdity of your argument is best illustrated by taking two full frame cameras with sensors of different resoltutions, equipping them with the same lens, and taking a picture with each camera. Now, the field of view is obviously the same on both of them and the pictures show the same scene. If we were then to print and examine them closely, the pictures would be exactly the same. If we were to look at the DOF calculator, however, it would show pretty different values of DOF for each of them.

In essence, your way of presenting the data would only be relevant if the resolution of the human eye that's looking at a same size pictore from the same distance were to magically change depending on the resolution of the camera that the picture was taken with.

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