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



On Tue, 17 Jul 2001 20:11:27 -0400  Austin Franklin 
(darkroom@ix.netcom.com) wrote:

> DMax is of no value what so ever unless there is a DMin associated with 
> it
> (and vice versa).

Hmm, I don't want to sound like a tiresome pedant who gets all worked up 
over precise use of language, but (to be tiresomely pedantic:) my point was 
that DMax *does* have a particular meaning in photography and it ain't 
'dynamic range'. It is an absolute value of opacity - a densitometric 
measurement relative only to the illuminant intensity unimpeded by film. 

This does matter, and is meaningful by itself, even within scanning. A 
scanner may not be able to cope, say, with a DMax of 4 although it can with 
a DMax of 3 (because it cannot increase illuminant intensity or 
integration time sufficiently). 

This is a separate parameter, distinct from Dmin or the dynamic range, aka 
Optical Density Range/ODR (difference between DMax and DMin).

Most scanners have fixed illuminant intensity, but if longer integration 
time is required, noise will increase.  Performance with a target DMax 4.0 
- DMin 1.0 ODR=3.0 is certain to be worse than with DMax 3.0 - DMin 0.0 
ODR=3.0. 

Although on the face of it you could describe the dynamic range as 3.0 in 
both cases, in the first you might lose a whole lot of shadow detail in 
extra noise. The extent to which this matters depends on the scanner and 
film base fog level, of course. But most do present CCD noise as a 
significant problem even with films with a low DMin.

> Typically, DMin is assumed to be 0 when DMax is used 
> by
> it self.

Yes, I know, but it's a misuse of terms really, and one which might make 
specs look better than they are. DMin never is 0 in real life, and 
pretending it is conveniently minimises the noise issues which arise with 
real film. An exaggerated dynamic range falls out of this simplification, 
to the benefit of marketing rather than accurate description, as far as I 
can see.


Regards 

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




 




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