[Leica] Leica Digilux 2 @ 1600 :-)

[henningw at archiphoto.com (Henning Wulff)]

At 9:08 AM +0200 9/3/04, Douglas M. Sharp wrote:
>Guten Tag Ted,
>That IS an interesting discovery, I tried something similar with my
>EOS300D/Digital Rebel at the weekend, I suppose it must work in the same
>way.
>I was shooting in a very dim chapel of remembrance in Berlin and was
>getting shutter speeds
>too slow for hand holding and didn't have a tripod with me. Shooting in
>RAW mode at 400 ASA I deliberately underexposed in manual metering mode
>and then corrected the image
>in Canons File viewer Facility (which allows the pre-processing of RAW
>images) to get
>back to the shutter speed I would have had to use according to the
>automatic mode.
>The shot turned out IMO better than I expected (within limits)
>see
>http://gallery.leica-users.org/New-Old-Pictures/Ged_chtnis_1
>
>I also read in a German photo publication that the ASA/ISO setting of
>100 is not necessarily better than
>at 200, though I didn't quite understand why, they even suggest avoiding
>the lowest value.
>In addition, shooting with higher ASA values, at least with the Canon,
>seems to make the files larger - any ideas/explanations on this count?
>greetings from sunny Northern Germany.
>Douglas

If you shoot at higher ISO values, you produce more noise, or pixels 
with values that have little to do with the scene values. In a 
simplified sense, JPEG works by describing a value for an area with 
similar values, so if there is a 'noise pixel', it has to be 
described separately, taking up more space in the file. In some 
cameras, shooting at the highest ISO can produce files that are 50% 
larger than the slow speed, smooth toned low ISO files of the same 
scene.

The 'underexpose' technique works just like pushing film. You're 
using just the most sensitive part of the film or sensor, and then in 
Photoshop you're 'overdeveloping'. With film this means that you get 
higher contrast, more grain and generally poorer tonal quality. With 
digital it means that you are getting more noise and getting poorer 
tones through something called 'banding', as you are expanding your 
finite number of digital levels that are useful to the total number 
of levels your printer can handle. With the standard JPEG files, you 
get 256 levels for each colour, and if you then only use the bottom 
50 (because the top 206 don't contain any useful info) and expand 
them into the 256 level space, you might find that these are too 
large 'steps' in some areas, resulting in a 'banded' look.

With a DSLR, shooting in RAW and producing a 16bit file with millions 
of values, this banding doesn't happen very easily because you might 
wind up using 'only' the bottom 10,000 values, as 16bit has over 
65,000 values for each colour. When you then get the file ready for 
printing, these 10,000 values easily get reduced to 256 that the 
printer can deal with.
-- 
    *            Henning J. Wulff
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