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RE: filmscanners: Scanner resolution (was: BWP seeks scanner)



On Mon, 18 Jun 2001 07:02:45 -0700  Shough, Dean (dean.shough@lmco.com) 
wrote:

> That is what MTFs (Modulation Transfer Function) are for.  The MTF for
> optical systems can be either computed (see Canon's EF Lens Work) or
> measured. 

Yes I know this, it is what I was referring to without calling it MTF - 
and my point was that Nyquist renders MTF incalculable for pixel-based 
*systems*. It is also difficult to measure sensibly, as the position and 
orientation of a conventional MTF target relative to the pixel locations 
affects the amount of aliasing and consequent artefacts. 

About all you can determine easily is the theoretical MTF 
possible at the CCD, according to the Nyquist limit, which tells you about 
as much about scanner system performance as an MTF test of film does about 
a camera/film system. We can't rip the lens out of these things and test 
them separately either.

There are special resolution targets available for empirical determination 
of pixel-based MTF - eg http://www.sinepatterns.com/ for targets made for 
scientific use - but I am not aware of any which are suitable for 35mm or 
other filmscanners. Sinepatterns would doubtless make one for a few 
thousand $$, but that is somewhat beyond my means;)

Regards 

Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner 
info & comparisons




 




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