Ooops! Sorry, I didn't know that Mike had posed this very question with
the very same distances and focal lengths to Dr. Focus. He went out for
a beer (well, some beers) a little while ago to see if he can keep the
label in focus throughout the night. Anyhow, I've answered for him.
He'll understand.
Chuck Norcutt
Chuck Norcutt wrote:
> 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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