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[OM] Re: Depth of field - the aha! factor

Subject: [OM] Re: Depth of field - the aha! factor
From: john@xxxxxxxxxxxxxxxx
Date: Mon, 20 Dec 2004 22:26:58 +0000
On Mon, 20 Dec 2004 09:04:42 -0500, Chuck Norcutt
<chucknorcutt@xxxxxxxxxxx> wrote:

>The ratio between the vertical size of a 35mm film frame and the Minolta 
>A1's sensor is 24mm/6.6mm = 3.64.  Using the free DoF calculator I 
>mentioned earlier at the Digital Light & Color site 
><http://www.dl-c.com/Temp/> I noticed that, applying the ratio above to 
>focal length, f-stop and resolution yields the same DoF.

Although I have understood the priniples behind DOF for a long time
(and came to the same general conclusions as Chuck has found from the
DLC site) I have often pondered the following.

My first camera was a Box Brownie, which had an effective aperture of
about F9 and seemed to have a DOF that was larger than it should have
been (subjectively at least) for that aperture. One reason might have
been that most prints in those days were "contacts" (same size as
negative - 6x9). But could it also be that the best circle of
confusion for this single meniscus lens was bigger than we would
expect from a well corrected modern lens, so that the far and near
points at which the circle of confusion became noticeably worse were
therefore further apart? OK, so it was soft everywhere, but that made
the focus less critical and so the DOF bigger.

I hope you understand what I'm trying to say! If my hypothesis is
right then a "poor" lens will have a greater perceived DOF than a good
one.


Regards


John Gruffydd (Mold, Wales, UK)
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