Digital BW, The Print

Claude,

> > The best you get is 100, the WORST you get is 50.  In reality, you get a
> > range of 50-100.  The 50 would be called "RELIABLY".
> >
> > Austin
> >
>
> Correct me if I'm wrong, but historically, haven't we put the lens MTF in
> parallel with the film MTF? Like tow 100 ohm resistors in
> parallel and invert the
> sum of their inverses in the process? and is "reliably"/planning
> for worst
> case? According to this formula, if either of the MTFs is any
> lower, the total
> MTF would be less than 50, reliably. If there's a more accurate
> formula, please
> enlightent me.

Yes, electronically, 100 ohms in parallel with 100 ohms does give you 50
ohms, but electronics are not the same as optics and film.  Film records the
data just like a CCD array does, using discrete elements.  If the photons
being "measured" happen to fall right on the sensing area, it will record at
that resolution, if it happens to straddle two sensing areas, it'll record
half that resolution.  What you will get are values from %50 gray on two
adjacent sensing areas, to one %100 white and one %100 black (if you are
using a test pattern that is).  Of course, film grain size is random, but
still within a rather narrow size band.

It's more than a formula, it's an understanding.

Austin