[Leica] M8/M9 "pushed" ISO 640 better than 1250

[pklein at threshinc.com (Peter Klein)]

When the M8 first came out, some people reported that they got better 
low-light results by underexposing ISO 640 by one stop and compensating 
in their RAW developer, rather than setting the ISO to 1250.  I think 
Tina was one of them.  I tried this myself, didn't like either results 
much, and have pretty much stuck to ISO 640 and lower.

Well, things have changed.  Today's RAW developers are better, and this 
approach does even better than before. I decided to revisit it with my 
M8 and the current Capture One v. 7.   The results are much better than 
I remember with Capture One v.4 (which came with the M8) or even Capture 
One v.6.  Here are a couple of real-world pictures taken in my den, with 
some deep shadows.

Here's ISO 640 pushed one stop (top) vs. 1250 (bottom):
<http://gallery.leica-users.org/d/366816-1/M8-640_1pushVs1250-NoNR.jpg 
<http://gallery.leica-users.org/d/366816-1/M8-640_1pushVs1250-NoNR.jpg>>

ISO 640 pushed two stops (top) vs. 2500 (bottom)
<http://gallery.leica-users.org/v/pklein/album170/M8-640_2pushVs2500-NoNR.jpg.html
 
<http://gallery.leica-users.org/v/pklein/album170/M8-640_2pushVs2500-NoNR.jpg.html>>

Dim tungsten light, fixed tungsten white balance "as shot" in camera. 
Sharpening and color NR was at default, and Luminance NR was turned off 
to see what we're really getting.

ISO 640 pushed one stop looks decidedly better than 1250 to my eyes. 
Quite usable, actually. I just got another stop out of my M8.

I wouldn't want to use either 2500 or 640 pushed two stops if I had a 
choice. The pushed 640 does look a little better. It might do in B&W 
with some careful NR and black point fussing.

If I recall correctly, C-1 v.7 shows the same default NR numbers for all 
ISOs. "50" is nominal, but behind the scenes it's applying more NR when 
the camera ISO is higher. My rule of thumb at higher ISOs is to keep the 
color NR at default, and use 1/4 to 1/2 the default luminance NR. And 
sometimes I just turn it off, as I prefer a little grit to the plastic 
look.  I'm still experimenting, but I have found that by raising the 
black point a little and using very sparing NR, the pushed ISO 640 
picture looks pretty good.  The 1250 picture is inherently more muddy 
and gets more smeary.

The point is that current RAW developers can push the M8 at least one 
stop, so you can get an effective ISO 1250 from 640.  The LUF thread 
shows that the M9 can be pushed even farther.  Current software is way 
better than turning up the electronic amplifier in the M8/9 beyond 640.  
Sure, the M240 and MM are objectively better high-ISO cameras. But if 
you don't wish to change cameras, there's life in that old CCD sensor yet.

There's a whole thread about this on l-camera-forum.com (LUF):
http://www.l-camera-forum.com/leica-forum/leica-m9-forum/301422-m9-iso-performance-new-life.html

--Peter