Archived posting to the Leica Users Group, 2001/04/02
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At 11:20 AM -0700 4/2/01, Paul Chefurka wrote:
> > -----Original Message-----
>> From: Austin Franklin [mailto:darkroom@ix.netcom.com]
>> Sent: Monday, April 02, 2001 1:33 PM
>> To: leica-users@mejac.palo-alto.ca.us
>> Subject: RE: [Leica] Re: film scanners
>>
>
>> A 14 bit A/D gives 16384 maximum unique values and Log 10 of
>> 16383 is 4.2,
>> which I am reasonably sure is what they are basing their
>> 'claim' on. It is
>> inaccurate (and misleading IMO) to make a claim based solely
>> on number of
>> bits. The spec should be based on overall system performance, not the
>> number of bits of the A/D.
>
>Has anyone heard any rumours about the "real" dynamic range of the
>4000 or 8000?
>
>Paul
Haven't heard anything yet, but if they can get these machines to
truly handle 2.6D Status A transparencies the world will be a better
place. As Austin pointed out, the claimed 4.2 density range refers to
the 14bits/channel that the electronics can process, and has little
to do with the actual dynamic range, or better yet, maximum density
range that they can handle.
The best photomultiplier imaging devices in drum scanners only get to
about 3.9, with the best CCD scanners using refrigerated devices to
reduce solid state background noise only get to about 3.0. Nikon
reduces the noise issue with its multi-scanning technique, but cannot
eliminate it. Also, CCD's have a certain non-linearity at the lower
input levels, resulting in a certain compression and limiting the
D-max capability.
Most well processed slide film today will produce 3.4D Status A
density in unexposed film, but an ability to read 2.6D would handle
most of our needs. I think the Imacon can handle 2.7D, and it can
produce excellent scans.
The hope is of course, that the new sensors in the Nikons are
actually able to read a higher D-max, and that the 14 bit electronics
aren't just hooked up to sensors with the same sensitivity.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com