Absolutely correct Walt in all respects. Though circle of confusion are
helpful!
--
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Walt Wayman
Sent: 19 December 2004 19:04
To: olympus@xxxxxxxxxx
Subject: [OM] Re: New member with question about 100/F2
I have and regularly use three 100mm lenses: 100/2 Zuiko with 35mm, 100/2.8
Zeiss Planar with 6x9cm Graflex XL, and 100/5.6 Schneider APO Symmar with
6x9cm Crown Graphic. At any given aperture, I am certain, and my experience
bolsters my certainty, that all three have exactly the same depth of field,
or depth of focus, whichever you prefer to call it. (Don't confuse me with
circles of confusion.)
However, it might seem that the two 6x9 lenses have a greater depth of
field, but that's only because a 6x9 negative or transparency doesn't have
to be enlarged nearly as much as a 35mm negative or transparency to make an
equal size print. But if we snip out a 24x36mm section from the center of
the 6x9cm negative or tranny and blow it up to the same degree as the 35mm,
it will look exactly the same in terms of depth of field. The more you
magnify the slightly out of focus parts, of course, the more out of focus
they look.
Wait a minute! I think I used this same "snipping out a piece" analogy a
while back in a discussion about focal length and perspective. But what the
hell! It applies here too. Focal length is focal length, and aperture has
the same relation to focal length no matter what the focal length happens to
be: the hole in the diaphragm has a diameter 1/x the focal length of the
lens, where x equals the f/number. (Don't confuse me with T-stops.)
I may be wrong, but I'm not really uncertain. However, I await correction.
Old as I am, I keep learning new stuff and unlearning old stuff I throught I
knew.
Walt
--
"Anything more than 500 yards from
the car just isn't photogenic." --
Edward Weston
-------------- Original message ----------------------
From: Fernando Gonzalez Gentile <fgnzalez@xxxxxxxxxxxxx>
>
>
> > From: "Piers Hemy" <piers@xxxxxxxx>
> > Reply-To: olympus@xxxxxxxxxx
> > Date: Sun, 19 Dec 2004 13:23:10 -0000
> > To: <olympus@xxxxxxxxxx>
> > Subject: [OM] Re: New member with question about 100/F2
> >
> > All 100mm lenses have the
> > same DoF. It depends how D0F is defined -
> [snip]
> > (and it is
> > also showing the shortcomings of a principle (DoF) defined in the
> > 1920s (if I remember correctly) .
>
> Could you elaborate or point towards more web published material on
> this subject, Piers?
> I supposed that the wider the aperture, the shallower the DOF; the
> longer the FL, the shallower the DOF.
> Wrong, isn't it?
>
> Thanks,
>
> Fernando.
>
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