Exactly. Skip explains it quite correctly, but allow me an example:
I have a 180mm Rodenstock lens I use fairly often with my 6x9cm Graflex XLRF.
If I were to take a photograph of an object from a fixed point with it on the
Graflex and the 180/2.8 Zuiko on an OM, assuming the same aperture is set on
each lens, if I cropped a 24x36mm section from the center of the 6x9cm
negative, it and the 35mm frame shot with the Zuiko would be, for all intents
and purposes, identical.
Walt
--
"Anything more than 500 yards from
the car just isn't photogenic." --
Edward Weston
-------------- Original message ----------------------
From: Skip Williams <om2@xxxxxxxxxxxxxxxx>
>
> > On a film camera, for a given focal length, as the format gets smaller, so
> > the
> DoF gets narrower.
>
> (I'm no optical engineer, just a hack.)
>
> Calculation of DOF is independent of the film/sensor size. This assumes that
> DOF is really a measure of apparant sharpness based on some minimum
> circle-of-confusion.
>
> A 300mm lens that has an image circle large enough to cover a 5x7 piece of
> film
> produces the exact same image size as a 300mm lens on a 4/3 camera. The 4/3
> camera only uses a small crop of the 5x7 lens' image. The DOF
> characteristics
> are the same. That's why you typically see LF photographers using f/45-128
> to
> get enough depth of field to cover reasonable subjects. You could stop a 4/3
> 300mm lens down to f/22 or so, but the long exposure times wouldn't make is
> usable, whereas the LF lens is used for fixed subjects.
>
> Your statement above should really say: As image magnification
> on-the-film/sensor stays constant, the DOF increases as the film/sensor
> format
> gets smaller.
>
> Skip
>
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