Re: 5% MTF "contrast" (TECH-3D digest 217)

[T3D John Ohrt <johrt@xxxxxxx>]

T3D Bob Howard wrote:

> Quotes from Lothar Koelsch, Head of Optical R&D Department Leica Gmbh.
> Article has some spot diagrams too and mentions their use!

I appreciate the reference and will try to look it up.  It is valuable to
have real world guidlines.

Not having read it, I can't understand how someone can relate lpm on the
negative presumably due to the limited lens rendition of observable
features without making reference to the degree of enlargement
anticipated.  For example, an extreme example, tech pan 2415 has a rated
resolution of 320 lpm and even some portrait photographers demand 1600
lpm in the lens to avoid unduly compromising the film resolution simply
because they are planing enlargement to something like 20x24.  Such
portraits are neither harsh or unpleasing.

My simplistic viewpoint is than when high resolution films and lens are
routinely used by non-scitech photographers, there must be some value,
but not that it is of use in all situations.

My one point were that 5% contrast is an user display requirement
independent of the medium of display.  Film and digital images can
capture at higher contrast and be manipulated to enhance that contrast
such that it is observable.  ie. the contrast must be 5% to be observable
by the eye, but the image contrast can be much lower and enhanced so that
the eye can observe it.

The other was that certain subject matter even in an artistic
presentation might benefit from contrast enhancement and that the
function was available in any software image processing or graphics
package that I have used.

As to how to use this artisitically, I don't know.  Maybe someday when I
develope an acceptable level of artistic sensibility I can be more
precise.  But beauty and elegance can be found in detail when you take
the time to look for it.

The only reason I remarked at all was that it appeared that some regarded
5% as the limit of useable contrast and that didn't happen to be the
case, even before digits started competing with chemistry.

Judging by the extreme opinions, and I do not mean yours, it would seem
that you could take a Realist and smear a heavy layer of vaseline over
the filters and the net result would always be acceptable.  I view such
as ludicrous as the other extreme that would require anyone to own a
Leica in order to take snapshots.

To bad you couldn't quote the whole article, but then as you pointed out,
that could cause all kinds of greif.

Thank you very much for pointing it out.

--

John Ohrt * Toronto * ON * Canada





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