Re: 2 1/4 vs 35mm, surprising DOF results

[George Huczek <ghuczek@sk.sympatico.ca>]

At 04:19 PM 12/08/97 -0500, you wrote:
>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?????????
>
It all depends on what the lens manufacturer considers to be an
"acceptable" limit for the circle of confusion.  Assigning a larger circle
of confusion makes it _seem_ as if the lens delivers more depth than it
actually does.  Leica lenses are assigned very small circles of confusion,
but that does not mean that they deliver less depth.  It means that there
are more critical limits set for what appears to be sharp. 

- -GH