Digital BW, The Print

Two thoughts:-

1) The big unknown here seems to be the noise in the readout amplifier
under real operating conditions. (The properties of sensor itself can
be guessed more easily as the physics is simple.)  The amplifier noise
sets the balance between readout time and dynamic range.  Astro CCDs
read fewer pixels much more slowly to reduce the effect of readout
noise.  I like the fast readout provided by my camera:)
I guess that the manufacturers take a system design approach to the
problem of handling the image information as it passes through
lens/microlens/filters/sensor/readout/gain/digitisation, balancing the
noise at each stage against cost, time to save image, etc. I don't
believe the ADC is the hardest part of the problem, and suspect that
extra bits would be used if they gave better images (at least in >$1k
cameras). Of course there is still room for improvement in all areas,
but it might not be very rapid.  

2) If we "expose to the right" we always have the same light on the
brightest pixel(s), for a given ISO, and lens and camera flare will
tend to produce perhaps of order 0.3% of this on the darkest pixel
(give or take - of course it varies by quite a lot from image to image
and lens to lens).  That corresponds to about 8 bits dynamic range.
Add another few bits to dig some detail out of the shadows/flare and
it seems to me that we don't have much to gain except in very special
circumstances. 
Of course one could argue that the lowering of shadow contrast by
flare means that we need more bits so that it can be expanded again in
raw conversion, but this really just fighting nature - a better
approach would be more contrasty lenses and good lens shades to reduce
flare and therefore require less expansion of the lower end.  

That is another reason why stacking differently-exposed images could
help, especially if the exposure change is achieved by putting an ND
filter over the lens to cut down the flare in absolute terms. (I'm not
sure how seriously this suggestion should be taken: a solid tripod is
needed and some care. I have never tried it - indeed don't have an ND
filter to hand.)  I think it could work quite well.  

From memory one of the big benefits of some medium format and most
large format film cameras was quite low flare compared to 35mm
(perhaps I am generalising too much, but it fits my experience) -
perhaps it is still true with MF digital backs?  

It would be interesting if someone has pointers to flare results to
make these numbers firmer, or if anyone has tried the ND filter trick.


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Jeff Medkeff
<medkeff@g...> wrote:
> Steve Kale wrote:
> 
> 
> > do you feel that for a given Canon
> > sensor (say the 1Ds MK II sensor) there is anything to be gained from
> > increasing the bit depth of the ADC?
> 
> Steve, in the specific case of the 1Ds Mark II, I do not think 
> additional bits (with higher sampling resolution) would be a gain. One 
> additional bit halves the gain and that seems like it would be too much 
> to me.