In message coh.net,
(Philip Homburg) wrote:

In article , wrote:
In message coh.net,
If you think a camera's metering is more accurate than the GN of a
speedlight flash, you put a lot of faith in the wrong things, IMO.

No, I think that a standalone light meter is designed to be accurate (around
D50).

And just how much do you think the flash, or shade, would affect the
reading? No frequency should vary more than about 1/3 stop between
"D50", and the meter isn't even narrow-band by any measure, just
slightly weighted.

What maximum RAW channel value do you think I would get on the 10D if I
had a D50 light source and an accurate meter calibrated to it, for 100%
reflectance?

Under no lighting situation that I've ever used my 10D with external
metering (incident or grey card), has 100% reflectance come anywhere
near the RAW maximum.

I state with 100% confidence that you can set your external meter to ISO
50 with the 10D set to ISO 50 (or 20D set to ISO 64), if you use
absolute exposure, and your brightest highlights are matte-reflective
only. If you need to capture detail in glare, or specular highlights,
then you might not get away with it (although the red and blue channels
will still have headroom to record greyscale highlights). Reflectance
of matte whites is usually 90% or less, and you may be able to push the
exposure more in some lighting.


Remember, the reputation that some DSLRs for blowing out highlights come
foremost from JPEGs that clip away RAW highlights, and even when the RAW
data itself is clipped, it is because the camera's AE increased the
exposure by a few stops because of weighted averages from the metering
(like a sliver of sky surrounded by shady city buildings on both sides
of the street). Incident metering rarely blows highlights and often
leaves headroom unused.
--


John P Sheehy