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RE: filmscanners: Nikon MF LED light source...





On Mon, 16 Jul 2001, Austin Franklin wrote:

> > I've also questioned Austin before (and agree with
> > your skepticism) that exposure times can be varied
> > willy-nilly with no effect on scan quality.  This
> > is quite contrary to my experience with film
> > scanners and photography in general.
> 
> Not only does the Leafscan manual say you can do this, and suggest doing it,
> but I've compared at least a dozen scans and there is no perceptible
> degradation in the image.
> 
> Obviously, if you have a Leafscan, you can do it your self, and for you
> Rafe, I'm happy to put two scans on a CD, or email you clips...


No need, Austin.  I'll take your word for it,
as it really isn't of great importance to me.

It just seems to defy logic, is all.  (Aside 
from making me doubt almost everything I 
thought I knew about scanners, CCDs, analog 
ciruitry, and A/Ds <g>.)

These "exposure" options -- what is the range 
of variations?  2:1? 4:1? 8:1?

Why would you ever use the "long" exposure 
option if the short one yielded a scan that 
was as good?

Only way to explain it is if the A/D has 
far more input range (and resolution) than 
is needed by the CCD, and *extremely* low 
noise, from CCD to A/D and all points between.

Either that or some non-electronic 
explanation, optical trickery (ND filters?) 
or other trickery -- like data being thrown 
out, or clock scaling or .... ???!?!?!

Makes my brain hurt just thinking about it.


rafe b.




 




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