Archived posting to the Leica Users Group, 2001/02/08
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Austing thought he was getting off easy... ;) He jotted down the following:
>> Martin wrote:
>> OK, explain how OPTICAL depth-of-field could exist independent of
>> (a) the essentially arbitrarily chosen 0.03mm CoC size,
>
> No one said the optical DOF doesn't have the COC as part of its equation.
OK, then provide the equation. Also, provide an explanation of how the CoC
is independent of the human perceptual system and therefore not dependent
upon an observer. Finally, please provide an explanation of how the CoC
size is derived.
>> (b) an observer.
>
> Is the number 3 the number three, even though no one is 'observing' it?
Irrelevant to the claims you are making. We're not talking about the mark
"3", or the concept of "three". We are talking about the concept and
manifestation of depth-of-field.
> It depends on what you mean by 'an observer'. Of course, if no one looks at
> 'it' then there is no consciousness of DOF, if that's what you mean. If you
> mean you NEED an observer to have DOF, that isn't the case.
You state that "optical" DOF (whatever that is) exists as an independent,
physical, and (in addition) measurable property. I would like you to show
how it could exist without the human perceptual system, or how it is
independent of the human perceptual system, and how it can be objectively
measured.
> It's not that hard...do you really want me to answer that? [how to measure
> "optical" DOF]
Yes. Since you are, to my knowledge, the only person ever to have claimed
that depth-of-field can be measured, as opposed to calculated, I would like
you to state how one goes about conducting this measurement, particularly if
it is that simple. I'm not trying to be cute, trite, or argumentative: I'm
genuinely interested in getting to the bottom of this and since you claim to
have the answers, you're the obvious person to ask to present them.
Please do not refer back to previous messages or vague claims that you've
already done this. Just post a simple message (perhaps collating and
clarifying previous material) which clearly shows:
(1) How the concept of depth-of-field can exist independent of
an observer. This, in turn, means showing that:
a) the size of the CoC is independent of the human perceptual
system;
b) how depth-of-field can be objectively measured. Not calculated,
but measured, and how the *value* of that measurement is obtained
independent of the peculiarities of the human perceptual system.
c) how the concept of depth-of-field would be unaltered if the
human perceptual system were, say, 100x better than it actually is.
(2) How what you call "optical" depth-of-field relates to, and is
conceptually different from, what you call "consciousness of DOF".
This would require you to show:
a) that there is a difference between CoCs on the film resulting
from depth-of-field and those resulting from a misaligned
film plane.
b) how these two are independent of each other.
c) that the "optical" component of these is independent of
viewing magnification, but the "consciousness" component is not.
Two simple points.
> You're the scholar, stop visiting and do something, like figure out how DOF
> can be measured ;-)
I have never claimed that DOF can be measured. As far as I'm concerned, it
can't be measured. It doesn't exist as an independent, objective property
of the world, so therefore it cannot be measured. It is a conceptual
construct used to understand how the limitations of the human visual system
relate to photography (or rather, the other way around). We exploit it in
everyday photography to control the appearance of "sharpness" of things
depicted in a photograph, but occasionally we run into surprises because of
misunderstandings of how the concept works.
You are the one who claimed it exists objectively and can be measured and I
think it is only reasonable to ask how one would go about doing that.
And it is because I'm a "scholar" (well, in training anyway ;) that I'm
asking you to present a plausible, coherent, congruent, consistent argument
for the claims that you are making: especially since they seem to fly in the
face of the other coherent, congruent, and consistent arguments for what
depth-of-field is and what properties the concept has.
M.
- --
Martin Howard |
Visiting Scholar, CSEL, OSU | "The future isn't what it used to be."
email: howard.390@osu.edu | -- Louis Cyphre (Angel Heart)
www: http://mvhoward.i.am/ +---------------------------------------