If you have the same image size on the sensor from two different focal
lengths both images will have exactly the same depth of field at the
same aperture.
For example; let's say that a particular flower fills the frame on an
E-3 from 1 foot with a 50mm DZ. If you're using a 100mm lens instead
then the same flower will fill the frame from 2 feet.
If you go through the DOF calculation using a resolution of 60 lines/mm
(CoC of 0.0167mm) and aperture of f/11, for 50mm at one foot you get
closest focus of 0.98 feet and farthest focus of 1.02 feet for a DOF of
0.04 feet. For the 100mm you get the same result. Nearest focus is
1.98 feet and furthest focus is 2.02 feet for a DOF of (once again) 0.04
feet.
Chuck Norcutt
Moose wrote:
>
> The thing I don't know about is DOF. My sense is that the trade-off for
> the working distance would be less DOF, but I can't do the juggling of
> different sensor sizes and focal lengths in my head.
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