Based on observation only, the K20 metering appears to be more accurate for RAW exposures than is that of the K10. I frequently find that exposures require no adjustment in white point of black point. I look at different values anyway but sometimes return to right at default for exposure brightness and shadow values (ACR). Paul On May 2, 2008, at 10:39 AM, Godfrey DiGiorgi wrote: > On May 2, 2008, at 1:37 AM, Davis, Lee wrote: > >> Are you saying that, regardless of whether you have the camera set to >> JPEG or RAW, the meter readout will always be the same for the given >> scene BUT that using RAW really needs extra exposure, > > Yes. > >> as if RAW and >> JPEGS were two different 'films', each having slightly different ISO >> ratings? > > Not quite ... With RAW, you have 12bit quantization, rather than > 8bit, and control of the gamma correction curve so you effectively > have more dynamic range to work with. > > Proper exposure technique for digital capture is to acquire as much > data as possible without saturating the sensor: the upper limit of > exposure has a hard edge at saturation, where the lower limit is > ultimately an arbitrary call to how much noise you find tolerable for > given scene dynamic. This is different from film exposure in that > film has a "soft" boundary at both ends of the spectrum. Since the > capture curve is a linear ramp in powers of 2, you want to get as > much data as close to saturation as possible: the top bit is half the > data, the next bit is 1/4, etc. > > Bruce Fraser explains this fundamental eloquently in the first > chapter or two of his book "Real World Camera Raw...". > > The *ist DS metering calibration for RAW capture was significantly > less accurate than the K10D. I have not experimented with a K20D to > know how it does. The R1 was shockingly accurate. > > >> At first, I was a little disappointed, thinking that many of the >> shots >> were up to a stop underexposed ... Even though we had even (though >> dull) >> lighting. The histograms are shifted to the left. In Lightroom the >> shots >> looked way too contrasty and muddy by default. >> >> I am also trialing Silkypix (too many variables here perhaps) and >> really >> like it. It seems to render the images better, less contrasty and >> perhaps brighter, by default. > > I rarely worry about the default settings in the RAW conversion > applications. Silkypix has perhaps better defaults but I absolutely > detest trying to work with it. Lightroom's defaults seem ok for a > good deal of stuff, but I hardly ever use default settings. > >> I got my Sony R1 out and started comparing its meter readings with >> the >> K20D for the same focal length shots, same ISO settings etc, set to >> RAW. >> (My neighbours must think I'm some sort of freak or nutter). Most >> of the >> time they were in agreement. What I did see though was that the >> K20D was >> *much* more sensitive ... Only a slight shift of the camera left or >> right would make it fluctuate. I wonder if the Pentaxes 'panic' if >> anything in the frame is considered a highlight, even on evaluative >> metering? For example, I only need to shift the K20D upwards >> slightly to >> include a small amount of extra sky and the meter reading changes. >> The >> Sony would need a little more of a shift. > > Sounds like the K20D has a more sharply defined metering pattern in > its evaluative mode, if that's the metering pattern you were using. > >> So, I am slightly confused but if it is generally true that cameras >> need >> or ought to meter differently for JPEG or RAW, then that is >> interesting >> stuff! > > A JPEG image is a rendered RGB image in a smaller quantization space, > post gamma correction. The gamma correction process is lossy: what is > lost in largest measure is dynamic range. So it should be no surprise > that the exposure requirements are different ... Kind of like > processing Plus-X in Microdol-X vs Acufine developer, you need to see > exposure on a different curve. > >> Why can't Pentax just make the firmware change this automtically? > > A simple bias adjustment is possible, but like so many ahoer aspects > of exposure evaluation, there are always mitigating circumstances > that might lead you to push the exposure in different directions. > Proper exposure is quite a serious study in finesse... > > Godfrey > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above > and follow the directions.
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