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[OM] Re: Figuring out depth of field with 4/3 adaptor

Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor
From: James Royall <james@xxxxxxxxxxxxx>
Date: Thu, 31 Mar 2005 08:02:25 +0100
I think the article that Radix posted the link to the other day has the 
most useful in the field guide, as we all have an idea of what kind of 
f stop we would use in a given situation with 35mm. The only thing I'm 
not completely sure of is what the focal length equivalence ratio will 
be for 4/3 system. It must be less than 1:4 as I think the sensors are 
larger than in the E-20.

James


http://www.wrotniak.net/photo/dof/index.html

"More, the relationship turns out to be quite simple. It can be 
summarized as

  The N-times-F Rule:

  The depth of field of a digital camera with a lens of the 1:N focal 
length equivalence ratio at a given F-setting is the same as that of a 
35 mm camera with a lens closed down to the aperture number of F 
multiplied by N.

  For almost all digital cameras (except models based on modified SLR 
bodies by Canon, Nikon, Sigma, and Contax), N varies between 4 and 5.5, 
hence difference is quite dramatic. The rule is accurate for all focal 
lengths and subject distances (there may be some deviations at macro 
settings), as well as for all focal length ratios (N-values).

  For example, an Olympus C-4000Z (1:5 ratio) at F/2.8 provides 
acceptable sharpness in the same range as a 35 mm camera with the lens 
closed down to F/14 i.e., 5*2.8 (at the same equivalent focal length, 
i.e., image angle). The Olympus E-20 has the focal length ratio of 1:4, 
therefore its lens at F/2.8 provides depth of field of an equivalent 
35-mm camera lens at F/11.2."




On 30 Mar 2005, at 06:17, Moose wrote:

> Joel Wilcox wrote:
>
>> <>But I thought Walt provided a good clear reference point from which 
>> to
>> think about the actual question. That's more than I had before. The
>> actual question is not that easy to answer, we have discovered.
>
> But there is an answer, and I'm on its trail....
>
> Moose
>
>
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