On Wed, 20 Jun 2001 07:55:14 -0700 Shough, Dean (dean.shough@lmco.com)
wrote:
> I'm not sure exactly what you mean about the Nyquist limit making the
> MTF
> incalculable or why you emphasize systems.
To counter the discussion hereabouts which is regarding the Nyquist limit
of the CCD as actual scanner resolution. This is usually going to be
overoptimistic, the optics and other facets of the system will degrade
real-life results. But there's no simple way to calculate this empirical
result, it needs to be measured.
> One can still measure the
> MTF
> for an optical system, even above the Nyquist limit.
Yes, exactly - as above.
> A straight
> foreword
> method for measuring MTF uses a sinusoidal pattern in front of the
> system
> and measures its response out the back.
No disagreement : my point was that conventional optical MTF test charts
are unsuitable.
> <<ISO 16067.jpg>>
Thanks for this.
> Again, I am not sure what you mean by this. When we place a test slide
> in a
> scanner and measure the scanner's MTF we are measuring the MTF for the
> entire system - optics, CCD, and electronics. Knowledge of the CCD's
> MTF
> provides us with an upper bound for what the MTF can be.
Sure :) I was arguing *for* *measurement* (vs. estimation or assumption
that CCD MTF=scanner MTF)
> Most of the patterns Sinepatterns makes are available off the shelf in 2
> inch squares and are suitable for testing 35 mm film scanners. But the
> costs start around US$700.
Really? For some reason I thought that most were 0.5"x0.5". However I went
through the site about 18m ago and once I found out costs I admit I didn't
pay much attention.
> Unfortunately the slide
> belongs to
> work. :-(
Just as a matter of interest, what material is this on?
Regards
Tony Sleep
- Online portfolio & exhibit; + film scanner
info & comparisons
