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Re: [OM] More on DOF and focal length (by Ctein)

Subject: Re: [OM] More on DOF and focal length (by Ctein)
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Mon, 29 Jun 2009 08:23:49 -0500
>
> The whole point of the article is that, after moving the camera to
> maintain the same magnification, the shorter lens will have greater
> total depth of field and proportionately more behind the subject rather
> than in front.  Any good depth of field calculator will show that to be
> true.  Changing image magnification in post processing without moving
> the camera is something that you and Jan have introduced.  It's not part
> of his argument at all since he doesn't even address it.
>


You need to read Ctein's comment on Thursday 1:01AM, copied below:
-----------------------

Dear Craig,

Yer right; Colin's comment slipped past me.

Yes, the two photographs were not made from the same location. I had to move
back about a dozen meters to get the same target magnification with the
telephoto lens as I'd gotten with the wide angle. So you'd expect the
composition to change.

Had I stayed in one place and made photos with two different lenses, the
composition would have stayed the same. I could have blown up the wide angle
photo and gotten the same composition as the telephoto picture.

BUT...

... and this is most curious ...

The two photographs would NOT exhibit the same DoF. The photo created with
the wider-angle lens will exhibit more DoF both in front of and behind the
target.

Bizarre, huh? Definitely counter-intuitive.

So cropping and enlarging a photo does not produce the same photograph as
changing lenses, although it does produce the same composition.

This one makes my head hurt.

pax / Ctein

--------------------------

AG
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