Archived posting to the Leica Users Group, 2000/11/09

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Subject: Re: [Leica] Re: DOF
From: Christer Almqvist <christer@almqvist.net>
Date: Thu, 9 Nov 2000 21:58:57 +0200
References: <5.0.0.25.0.20001109122440.00aab280@206.34.200.40>

>At 06:25 AM 11/9/00 -0800, you wrote:
>>If you crop a picture shot with a wide angle lens and then enlarge it
>>so it is comparable to a print made through a longer lens, the DOF
>>will be the same in both prints.  The actual lens doesn't affect DOF.
>
>um...not to be argumentative, but i disagree...
>I am considering DOF to be the point of nearest acceptable focus to 
>the point of farthest acceptable focus in any given image.  Like 
>Perspective, it is set on the negative as a latent image by your 
>choice of lens and aperture. Nothing you do to it during or after 
>development of the negative can change the DOF (or perspective such 
>as apparent background compression.) You can change Composition and 
>other characteristics (Gamma, RGB, hue, contrast, etc..) in the wet 
>or digital lab, but Depth of Field, Focus and Perspective are 
>determined in camera.
>
>Carpe Luminem,
>Michael E. Berube

(I presume we agree that sharpness is not  equal  throughout the 
range of distance which we call DOF, but drops constantly as we get 
further away (in both directions) from the point which is in perfect 
focus.)  We certainly agree that the DOF covers a larger range behind 
and in front of  the subject on which we focus if we use a 21 mm lens 
than if we use a 90 mm lens provided the camera to subject distance 
and the aperture are  the same in both cases. However, if you want 
the subject to be the same size when you print your negatives, then 
you will have to enlarge your 21mm negative more than the 90 mm 
negative and those things just on the DOF limit of the 21 mm lens 
will then, on the print, have more or less the same sharpness as 
those same things will have on the print made from the 90 mm  lens 
negative as the 90 mm negatiive require less enlargement.  Of course, 
many other factor come into play, including the quality of your film 
and processing.

I do not think perspective is set by your choice of lens and 
aperture. I think it is dependent on the relative distances between 
the subjects photographed and the camera. Look at the final prints of 
pictures made with different focal lengths, but make sure they  show 
exactly the same things, no less no more. If the pictures you compare 
do not show exactly the same thing, then your are discussing cropping 
and picture content, not perspective.


(I looke at wour werb site and conclude we also disagree on ties and 
bow ties  ; -)



- -- 
Christer Almqvist
D-20255 Hamburg, Germany and/or
F-50590 Regnéville-sur-Mer, France

In reply to: Message from "M.E.Berube" <MEB@goodphotos.com> (Re: [Leica] Re: DOF)