Hmmmm, now lets see...
Yes, if you look at the picture from the same distance, you will sense
that the DOF is larger if the magnification is less. But, if the
picture is the same then you reduce the size of the print and the
viewer will go closer and adjust the sensed magnification. If that is
the case the viewer will sense the same DOF.
If you reduce the magnification while the print size is constant then
you have changed the lens, the size of the image sensor/film or a
little of both, in which case the viewer will keep the same distance
(unless he wants to look at some detail) and sense a different DOF.
The effective resolution limits the possible magnification, viewing
distance, and the possible range of DOF.
But this is theory not practice. In real life people usually don´t let
the sensor/film decide the size of the print. They want a print this
size and they like the effects your photograph has in that size. In
that sense the larger resolution, once it is sufficient at a certain
viewing distance, has the effect of giving a possibility of moving in
closer letting the image fill you field of view and at the same time
see more details. In that process you can say that the DOF changes as
you move into the picture. The sensed magnification changes as well as
the DOF.
So in some ways you are both right.
(and by the way JCO, I´ve been making my own prints since 1977 so don
´t use your experience, it´s not enough :-)
DagT
Den 7. april. 2009 kl. 21.53 skrev JC OConnell:
I already stated you can choose ANY reference you
want ( a particular COC for example) it doesnt matter,
if you want to increase or decrease DOF, regardless
of your reference, only image mag/f-stop can CHANGE it.
I think what your trying to do is define DOF absolutely,
via a maximum COC for example. This is fine if you know
and understand that concept. But changing your COC size
only changes the way you MEASURE the DOF, it doesnt
change the actual DOF. IF if WANT more or less DOF
it does not matter how you define/reference it, only MAG/FSTOP
changes will increase/decrease the DOF ***COMPARED
TO YOUR REFERENCE, WHATEVER YOU CHOOSE*** All the other
varibles cancel out and your left with only MAG and F-STOP
to increase/decrease DOF.
JC O'Connell
hifis...@gate.net
-----Original Message-----
From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf
Of
Bob W
Sent: Tuesday, April 07, 2009 3:41 PM
To: 'Pentax-Discuss Mail List'
Subject: RE: Trading resolution for depth of field
Sir,
MY "burden of proof" is no greater than yours.
If you cant provide any reliable "proof"
that my contention is not true, then
your word is no better than mine.
You haven't supplied us with anything that is falsifiable. All you've
given us is unsupported assertions.
I dont need
any more "proof" to support my contention than
you need to support yours.
I've provided you with definitions of terms, a mathematical formula
and
a published reference. Others have pointed you to definitions and
formulae which state the same thing as me, and which also have
published
references, including references from companies such as Kodak and
Zeiss
and the leading optical scientists.
This is very simple. DOF is all about magnfication
and f-stop.
I did supply the formula,
relative DOF = F-stop number/MAGNIFICATION.
INCREASING F-STOP NUMBER OR DECREASING IMAGE MAGINIFICATION increases
the image relative DOF.
Conversely,
DECREASING THE F-STOP NUMBER OR INCREASING THE
MAGNIFICATION decreases the image relative DOF.
If you dont believe me, do some experiments.
I have, its called about 35 years of practical
experience to back up what I have read in theory.
This isn't my theory, this is the correct theory
that I have read and found to be true over the years.
I have as much experience of practical photography as you do. I can
cite
theory, and I can provide references. You cannot provide references,
and
the formulae you have provided do not include definitions of terms
(such
as DOF), so they're useless.
Give us a respectable reference which supports your claim and these
so-called formulae.
Bob
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