Just when I thought I had this understood, I was researching
"exposure" postings from the various forums & now I'm very confused.
My questions are:
1). When should one use a Grey Card & the proper way of setting the wb
2). When should one use a White Card & the proper way of setting
the wb
3). When should one use a pringles lid & the proper way of setting
the wb
4). Should a combination of either a Grey Card, White Card or
pringles be used together? If so, what is the proper way of doing
so?
The replys varied so much on the different forms it confused me & I
want to make sure im doing things right.
I've been studying this a little lately, and I can give you some
preliminary results.
I bought an Expodisc, which is the real (calibrated) version of the
Pringles lid. I studied their literature closely, which literature
is not very well written, and I think I have the basic concept of
how they expect us to use it.
I went out with a notebook, my E20, the Expodisc, and an incident
light meter. I checked the exposure readings with the meter, the
Expodisc pointed back at the light source as an incident meter, and
the camera's reflected light metering in center weighted averaging.
The readings varied greatly for the same scene. For example, for
one normal, sunlit scene, the incident meter wanted 1/500 at f8,
the Expodisc as incident meter wanted 1/500 at f7.1, and the camera
pointed at the scene wanted 1/500 at f3.6!
The camera's reflected light reading was almost always right, as
judged by eye and the histogram afterwards. In general, it seems
that the incident meter (all set to ISO 80) was one stop darker
than the camera acting as incident meter with the Expodisc, and the
camera's reflected reading was a stop brighter than that, and was
more correct.
All of this was with normal front lighting. When you have side or
backlit subjects, it gets a lot trickier, and it is impossible to
avoid using some judgement about what results you want. I think
this is where the cameras with electronic viewfinders rather than
the optical would shine. They show exactly what results are being
recorded. The E20 also has live preview, but it requires a hood,
hopefully with magnifier, to be able to use it as an electronic
viewfinder in daylight.
Be that as it may, the answer to your question is that pointing
your camera at a grey card and taking a reflected light reading
from it is equivalent to putting the Expodisc on it and using it as
an incident meter. Not quite as accurate as using the actual
subject to meter on.
As for white balance, you can WB on either a white or a grey card,
or use something like the Expodisc or Pringles lid aimed toward the
light source. They will give a very good WB reading, but so will
Auto in daylight. Indoors, balance on a white (or neutral grey)
object or do the same Expodisc trick as before. Should be exactly
equivalent.
To summarize, the camera's reflected light meter is your best tool
for exposure, but you should intelligently aim the center spot at
the part of the image that you want to expose for. Maybe even check
several areas of the image. Maybe even bracket or check histograms
on playback. Digital's latitude is so narrow we must expose for
what we want in the original image, because it is more difficult to
fix it in post.
Gary Eickmeier
D (roflmao)