[Leica] Don't diss my MTF

["Jonathan Borden" <jborden@mediaone.net>]

Martin Howard wrote:
(hazy stuff clipped)
>
> You mentioned yourself: "...assuming you believe in systems theory".
That's
> the key, it's a theory.  ...

    Where to start? the use of the term "Theory" in science means something
which is generally held to be valid.  The suitability of the optical
theories mentioned are that they are used by optical designers to create the
latest generation of lenses. If you like any of the Leica ASPH lenses (or
Schneider or Zeiss etc.), you ought appreciate the theory that allows these
lenses to be designed. The "proof" is in the pudding, so to speak.

>
> Even if the concept of bokeh is captured by the MTF theory, every single
> practical MTF test I have ever seen has looked at how the lens renders
> something that it is focussed upon (usually at infinity).  Not how it
> renders something that it is *not* focussed on, either infront of or
behind
> the plane of focus.
>
> We observe what we know to look for.
>

And you appear to know only what you have yourself seen.  Without getting
overly technical, the MTF as commonly published is a subset of or otherwise
related to something called a "deconvolution kernel" which is a 3
dimensional <phase, frequency> response, or point spread function of the
lens. The point spread function strongly depends on out of focus
information.

There are a few talks on the web which explain this in more detail for the
technically inclined:
http://www30.accu.nl/talks/talksIndex.html

This is not some mamby pamby flaky theory subject to debate about what is or
isn't science. This is science by any definition of the term. E. Leitz would
strongly approve!

"Bokeh" on the other hand is a term which describes in English :-)) actually
Japanese, the appearence of the out of focus parts of the photograph
produced by the lens. There is nothing wrong with that, just don't diss my
MTF.


Jonathan Borden