Archived posting to the Leica Users Group, 2003/07/31

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Subject: [Leica] Off to Alaska, Digital characteristic curves
From: "Mark Davison" <mark_e_davison@msn.com>
Date: Thu, 31 Jul 2003 15:13:44 +0000

I'm off to Alaska for a cruise with family and mother-in-law. I've been 
lurking on the list for the last month or so.

After much soul searching I am only taking my N*k*n film SLR. I put together 
a kit with Leica M and  the SLR but decided it just wasn't worth carting all 
that stuff around to photograph glaciers and eagles. I guess I was inspired 
by the "less is more" discussions, even though it means leaving the beloved 
M camera at home.

I decided against my D100 because it just doesn't do well in high contrast 
situations, and I'm hoping there will be some good days with bright light.

Being a techie by nature, I plotted out the characteristic curve of my D100 
(digital output vs. exposure measured in stops.) You get what looks like a 
power curve, with a long long toe, rising up to an extinction point at about 
2.5 stops above metered exposure. There is no shoulder, and the slope of the 
curve is alway increasing. The metered exposure gives an output of about 97, 
which is below what you would expect (128). Without adjustment in Photoshop, 
the images coming out of the camera have very dark shadows, muddy midtones, 
and highlights with excessive contrast, just as the characteristic curve 
would predict.

The practical result is that in high contrast situations you must carefully 
meter for the highlights with the spot meter, or they will be mercilessly 
clipped, leaving daubs of brilliant flat white in your picture, where there 
used to be white shirts, glaciers, peoples foreheads etc. Exposing for the 
highlights makes the midtones quite dark, and often pushes the shadows into 
the dreaded basement of weird digital noise.

Have any of you plotted characteristic curves for the Digilux or LC5? Do 
they show similar characteristics?

Mark Davison

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