[Leica] Re: the dynamic range of digital

[henningw at archiphoto.com (Henning Wulff)]

>I have experience with three Nikon DSLRs:  the D100, D2h, and D200.
>
>On each camera I have performed George's suggested experiment of 
>shooting a textured card to find out when the camera will blow the 
>highlights.
>
>The results are nearly uniform, with some minor variation depending 
>on whether you shoot .jpeg or .nef (Nikon's RAW format).
>
>The sensor clips hard at around 2 stops "overexposure", or more 
>precisely, 2 stops exposure greater than the metered value.
>
>There is usable data down to about 5 stops "underexposure", or more 
>precisely, 5 stops exposure less than the metered value. There is 
>visible data with more stops underexposure, but it is filled with 
>ugly noise.  (This result depends to a great degree on what ISO you 
>have set, and to what extent you are willing to peform noise 
>reduction in software outside the camera.)
>
>Therefore the meter is calibrated to give a response range which is 
>not symmetric around the metered exposure.
>
>If you are shooting in flat light, where there is no more than 4 
>stops of scene brightness range (+ and - 2 stops from the metered 
>value) then you do not need exposure compensation.
>
>In contrasty light, I typically find I have at least 6 stops of 
>scene brightness range (+ and - 3 stops from the metered value) and 
>need to introduce an exposure compensation of -1 stop (when using 
>the Nikon matrix metering.)
>
>When I dial in -1 exposure compensation when shooting in contrasty 
>light, I am not "underexposing"--I am just biasing my exposure to 
>correct for the meter's calibration, in order to place the histogram 
>just to the right. Another way to think about it is that I am 
>fitting the scene brightness range into the recording range of the 
>camera's sensor.
>
>When shooting static subjects (like landscapes) you can take the 
>time to spot meter the brightest highlight where you want to record 
>detail, and then expose about 1 and 2/3 stops more.  In zone system 
>parlance you are "placing" the highlight at Zone 6 and 2/3. I then 
>look at the histogram(s) and make further small adjustments.
>
>In shooting sports on bright contrasty days, I sometimes take test 
>shots and adjust my exposure compensation to get the R,G,B histogram 
>right.  This allows me to tailor the exposure compensation to 
>prevailing conditions.
>
>One weakness of the D100 and D2h is the lack of separate R, G, and B 
>histograms--these cameras appear to simply use the G channel to 
>represent luminosity.  This can lead to blowing the R channel when 
>shooting flowers, sunsets, and red soccer jerseys and you get 
>strange color shifts.
>
>When I get time I'll check the sensor response of my R-D1 and report on 
>that.
>
>I hope my Nikon experience helps others.
>
>Has anyone done these experiments with any of the Canon DSLRs?  Do 
>they center the recordable brightness range around the metered 
>value, or do they clip at the same 2 stops over the metered value? 
>How about the Olympus 4/3 cameras?
>
>Please note that the poor camera engineers have a hard choice to 
>make in setting the meter calibration.  Setting the meter to read 2 
>stops below highlight saturation makes full use of the sensor range 
>when shooting in flat light (giving the most accurate tonal detail), 
>but it ensures blown highlights when shooting in contrasty light.
>
>Also note that careful metering with an incident meter does not 
>change the problem.  If there are objects in the scene which spot 
>meter more than 2 stops over the incident meter reading, then they 
>will become blown highlights if the you set the camera to the 
>exposure from the incident meter.
>
>Mark Davison

I haven't done a rigorous test on my Canons like you have, Mark, but 
the result is the same. In flat light I can meter straight; in very 
flat light, like when shooting a telephoto through haze, I dial in as 
much as +1.3 to shift the recorded data as far to the right. That 
way, when I expand the dynamic range in PS, I have enough data to 
work with.

In very contrasty light I set the compensation to as much as -1.3 or 
even at times -2 if the highlights are to be fully recorded. Again, 
under new and especially difficult lighting conditions I take a 
couple of shots and examine the histograms (RGB if possible) and set 
the compensation accordingly..

This way I generally avoid having to bracket like I would with film 
in extremely contrasty conditions, although I sometimes still do, and 
I'm ready to react to photo opportunities that pop up quickly under 
those conditions. A real advantage with digital.

-- 
    *            Henning J. Wulff
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