aperture, FL, sensor size and DOF

Started Aug 19, 2012 | Discussions thread
Detail Man
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Re: aperture, FL, sensor size and DOF
In reply to ennemkay, Aug 22, 2012

Detail Man wrote:

ennemkay wrote:

Great, thanks for the replies. I'll bookmark that other thread. In particular I was trying to compare the dof capabilities of the nex 55-210 f4.5-6.3 and panny 45-200 f4-5.6.

The sensor-size is a factor in determining the DOF, as well (see the first formula in the linked post).

Seems like the nex lens will provide noticeably shallower dof at the extremes.

I think that you may be missing my point. Consider the lenses that you mention, the same camera-subject distance, the same Focal Length, and the same F-Number. The image that you record with the NEX will not be the same image that you record with the M43 camera system. Because of the larger sensor-size, the image recorded using the NEX will include more of the scene in the vertical and horizontal axes. So, then you crop the NEX image in post-processing so that both recorded images are the same , and view them at the same print/display size from the same viewing distance

Cropping-down the NEX image reduces the calculated DOF - by an amount that is exactly equal to the difference in the image-sensor sizes (linear dimensions). Guess what. The DOF is the same .

Had you (instead of post-cropping) increased the Focal Length of the lens on the NEX (so that the image that was recorded on the NEX had been the same image as the image that was recorded on the M43 camera), and increased the F-Number of the lens on the NEX by an amount equal to the ratio of the Focal Length of the lens on the NEX divided by the Focal Length of the lens on the M43 camera, then the DOF of the two recorded images would have been exactly the same ...

ennemkay wrote:

Same 35mm-equiv fl, yes.

Note that the relevant formulas (in the post again linked-to below) use actual Focal Lengths only:

http://forums.dpreview.com/forums/read.asp?forum=1041&message=42069700

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