Digital BW, The Print

Claude,

> > It's more than a formula, it's an understanding.
> >
> > Austin
> >
>
> The electronic analogy was merely to point out the classic
> formula used to
> figure out system MTF between lenses and film. The
> "understanding" that you
> outline concerning "straddling" two sensing areas is precisely
> what is taken into
> account with the formula.

Some things ARE 1/x + 1/x etc (like the resistors), and some things are not,
and understanding enough to know when some are and some aren't is the
understanding I was mentioning you apparently don't have.  Straddling gives
you the WORST case, and aligned gives you the best case.  There is no such
thing as "straddling" with respect to resistors, but there IS when respect
to sampling.  Resistors are not sampling, but imaging is.

> The accepted formula for doing so, in all literature I have ever
> come across
> is to invert the sum of their inverses.  So, 1/100 is 0.01 for
> the film and
> lens. If we add 0.01 + 0.01 = 0.02. Now taking the inverse of
> 0.02 (1/.02), we
> get 50. This is the BEST possible performance we can expect with a high
> contrast subject, with the lens and film working together. If
> either one of them is
> slightly lower (usually the lens), then the system drops to less
> than 50 LPPMM.

Your statement that started this was about DIGITAL sensors, BTW, which is an
easier example to show you're incorrect.  If you have a lense that gives 100
lp/mm and a sensor that is also, say, 100 lp/mm, then you CAN IN FACT get
100 lp/mm at the sensor if the.  You can only RELIABLY get 50, but in
reality you get a range of between 50 and 100.  This is just plain and
simple fact of sample theory, and if you just don't understand it, well,
then you just don't understand it.

> Your reasoning sounds good, but it doesn't appear to be congruous
> with the
> traditional formulas cited above.

Since you obviously don't actually understand how the system works, or the
actual dynamics of "the formula", or how it actually applies, you're going
to draw erroneous conclusions.

Austin