Archived posting to the Leica Users Group, 2004/02/19

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Subject: RE: [Leica] Digital DOF
From: "Don Dory" <dorysrus@mindspring.com>
Date: Thu, 19 Feb 2004 21:51:10 -0500

Jacques:
It is not the sensor size that is determining the DOF.  It is the lens
focal length.  On a small P&S digital you might have a 5-16mm focal
length zoom roughly equivalent in image magnification to a 35-105 in
35mm.  So if you were doing a portrait using the 16mm focal length on
the P&S and a 100mm on the 35mm from the same position and aperture then
you would indeed have very different DOF on any reasonable image size.
Now, if I used a 16mm lens on my 35mm and cropped to the same image size
then the DOF would be the same assuming the same aperture, distance to
subject, and image size on finished image.

Some of the confusion is coming from magnification factors with digital
SLR's using different focal length lenses to put the same image on the
ground glass.  Using the E-1 as an example, a 50mm lens magnifies like a
100mm on a full frame digital or normal 35mm.  The 50mm retains the same
DOF properties that it would have on 35mm so the DOF using the Olympus
system at a given aperture and image magnification would be greater than
the DOF that would happen with a 35mm system, 100mm lens, same aperture,
and same image magnification.

I hope that this helps.

- -----Original Message-----
From: owner-leica-users@mejac.palo-alto.ca.us
[mailto:owner-leica-users@mejac.palo-alto.ca.us] On Behalf Of Jacques
Bilinski & Barbara Bradbury
Sent: Thursday, February 19, 2004 5:40 PM
To: leica-users@mejac.palo-alto.ca.us
Subject: Re: [Leica] Digital DOF



> 1) Sorry, not right. Increasing magnification, and keeping the other
> variables the same: shooting distance, aperture and output -- say 4x6
> print at 18 inches, you are reducing apparent DOF.
>
I'm still having trouble with this. I thought that a major complaint of
the
small sensor digital cameras was that you cannot shoot portraits with
the
background out of focus like you can with 35mm. So if you take 2
pictures -
one with a small sensor digital and one with a 35mm from the same
location
(same perspective, different focal lengths, same f stop), and then print
both on a say 4x6 print. Will not the 35mm shot show a more out of focus
background?

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Replies: Reply from Henning Wulff <henningw@archiphoto.com> (RE: [Leica] Digital DOF)