Archived posting to the Leica Users Group, 1997/08/12

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Subject: 2 1/4 vs 35mm, surprising DOF results
From: "BIRKEY, DUANE" <dbirkey@hcjb.org.ec>
Date: Tue, 12 Aug 1997 16:19:56 -0500

Curt Miller wrote:

>If there are any doubters among us, just get out a 50 Leica lens and =

an 80
>Hassy lens (or a 35 Leica and a 50 Hassy).  See what the DOF scales =

show for
>f/8 (or F/whatever you choose).

>Think this is sort of a common misperception about applied optical =

theory.

Gee, I was always told that at a 50 is a 50 is a 50.  That the depth of =

field for any 50mm lens, no matter the format, is always the same, just =

more or less coverage.

Hoping that I was right, I decided to check it out on a couple lenses.  =

Are you sitting down???  The Canon FD 35mm lens at f/16 shows about 4ft =

to infinity.  A Mamiya 35mm C at f/16 says about 2.3 ft to infinity.    =

Yes that's right, the Mamiya says it has more depth of field.  I =

couldn't believe it.  So I compared another.  The Canon FD 85mm at f/22 =

says 15ft to infinity.  The Mamiya 80 C  at f/22 says 7 feet to =

infinity.   How can this be?????????

My real world experience tells me this Mamiya 35C doesn't deliver sharp =

images period.  Someone at  Mamiya had to be playing with those circle =

of diffusion numbers to show that the Mamiya has more "depth of field". =

  Anyhow,  if I'm shooting at f/16 I usually set the infinity mark to =

around f/8 as a safety margin and sometimes bracket focus if it's =

really critical.

Theory is fine, but doesn't always play out in practice.   Sorry, I =

don't have equivalent Leica lenses to compare yet.

Duane Birkey
HCJB World Radio
Quito Ecuador

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