Digital BW, The Print

> Then again, I'm a pragmatist.  I'm not going to wait for a sensor
> breakthrough.  I can live with 12 bits as long as my image range
fits the
> range of the sensor.  That's what the old timers did before graded
paper.
> So, I'll just tune the system, like the old zone system, so that
happens.
> 
> Paul
> www.PaulRoark.com
Many of us take pictures of static subjects - then the simple way to
extend dynamic range is to take multiple shots with differing shutter
speed, then stack them into one image (for which I find Picture Window
Pro useful).  It is "easy" to get more range
than cameras will deliver in 5 years time - indeed more than can be
stored in a 16-bit file... Problem is that it gets even harder to
compress this range on to a print .... very complicated characteristic
curves take a long time to get right.  Strangely I've never found the
final print to be very much better than just the straight exposure,
but I'm sure that is my fault.

Similarly the cheap way to get more pixels for bigger prints (or
smaller artifacts) is to join multiple images (yesterday I took 10
pitcures, 8 were made from between 2 and 4 300D shots, total
processing about 1 hour, 5 printed).  Big advantage of this is the
lens appears better too (whereas more pixels in the camera don't help
much there).  In this case the pictures nearly always look better than
the single frames (and with some lenses effective depth of field can
be extended too, by careful focussing).  Speed is of the essence if
the light changes - 350/RebelXT is better than my 300D in this
respect.

The knowledge in this thread is fundamental to digital photography.

On some of the points that arose earlier:- 

From experiment it seems that the quantum efficiency figure of around
25% is about right, and with not-too-long exposures Canon (for
example) has done a great job in keeping amplifier/readout noise down
so that we can make use of the high QE, while not having to wait a
long time to read out each frame (the faster the readout the quieter
the amplifier needs to be to "read" the number of photons in the well
in time).  

The end result is that we see very low noise compared to film (QE<<1%)
of the same effective speed (by which I mean the ISO taking into
account relative frame size).  Another way to say this is that the
sensor noise for the whole image, samples into a given number of
pixels, is equivalent to film larger in area
by the ratio of QE (i.e. >25 times, or >5 times in linear measure).
 
The low noise allows us to sharpen images and obtain good contrast in
the mid-range of spatial frequencies in the image (more important in
real images than the extinction resolution - where film wins).  That
is why I love digital images. 

Of course the cost of flexibility is the need to understand what one
is doing to keep the process under control - in that sense it is
harder than with film, where choices were more limited.