I also found it a useful article.
Focal length equivalence ratio for 4/3 is 1:2
35mm frame: 36mm x 24mm = diagonal = 43.5mm
4/3 frame: 18mm x 13.5mm = diagonal 22.5mm
See http://www.four-thirds.com/about.htm
--
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of James Royall
Sent: 31 March 2005 08:02
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor
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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