Depth of field of 4/3 or m4/3

Started Nov 3, 2010 | Discussions thread
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jpzundel Forum Member • Posts: 75
Depth of field of 4/3 or m4/3

I am unhappy to read so many half-truths about depth of field and how 4/3 have systematically smaller DOF than other sensors.

Depth of field depends on f stop and subject magnification only.

So the DOF of a 20mm 1.7 on 4/3 is the same as the DOF of a 40mm 1.7 on 35mm for the same subject magnification.

Unless someone teaches me something new, these statements about DOF of 4/3 being less because it is a smaller sensor are false.

DOF is pure geometry.
When the geometry is the same, never mind the scale, DOF is the same.

I.e. same f stop and same magnification give same geometry to the image making light rays therefore the same circle of confusion relative to the whole image.
Trace the rays, it will be obvious.

Actually DOF does not depend on focal length either, only on f stop and magnification. That should be a surprise to most.

An image of the same magnification of the subject has the same depth of field, be it taken with a 20mm or an 80mm. Of course you have to stand much further with the 80mm to have the same magnification as with a 20mm.

Try it. Take picture with the same f stop and same subject size in the final image, and the DOF will be the same whether taken with an 8mm or a 100mm.

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