Bruce Girrell on tue 21 mar 00
>> nothing like a hand held light meter. used, 75 bucks. last forever
>> and they can be taken in and calibrated.
>Right again, mel! In fact, I would go one step further. Not only
>should you get a hand-held meter, you should also get a photo-grey card.
Sorry, I have to jump in here one more time.
Hand-held meters and gray cards are fine. I use them myself, especially for
the view camera, on which through-the-lens metering is almost impossible.
But...
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* You must be aware of what you are measuring and how to interpret it. *
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First, if your camera meter does not match the hand-held meter, take them to
a camera shop and get them calibrated. They should agree. Take your lens in
also. Maybe there's a problem with the aperture diaphragm that is messing up
the reading. From this point on, I'll assume that the hand-held meter and
camera read the same, given equal conditions.
Second, to interpret a hand-held meter reading properly you must account for
any filtration that you place in front of the camera's lens, especially a
polarizer. Polarizers can decrease the exposure by over 2 stops. Other
filters, such as warming (yellow) or cooling (blue) filters usually affect
the exposure by 1/3 to 1 stop.
Third, at close distances - which we are talking about with shots of pots -
the amount of light reaching the film through the lens is decreased compared
to the same lens focused at infinity. You must also account for this effect
when using a hand-held meter.
Finally, when you meter a gray card, you will get an exposure that is
correct for an average subject. This is what Paul was getting at. If you
meter a light colored pot, the meter will give you an exposure reading that
would represent the pot as having the same reflectance as an 18% gray card.
In other words, the pot will be dark (underexposed). If you meter a dark
colored pot, once again the meter will give you an exposure that would
represent the pot as having a reflectance of an 18% gray card, yielding a
photo that will be too light (overexposed). By metering the gray card
instead of the pot you eliminate variations resulting from the color of the
pot.
However, there can still be problems. When we take photos of pots, we tend
to fill as much of the frame with the pot as possible. This, incidentally,
is what trips up the automatic printers at the local one-hour shop. What
constitutes an "average" photo (represented by the gray card) is no longer
valid when most of the frame is filled with a single object.
If you really want to know how to use a hand-held meter or to properly
interpret the readings provided by your camera's meter, learn about the Zone
System. The Zone System was developed by Ansel Adams so that he could
produce predictable results for black-and-white photos. In it's full-blown
form, the Zone System will calibrate you, your camera, your light meter, the
processing, and, if appropriate, the printing so that you can produce the
same results every time. See http://www.zonesystem.com/ for details.
While the Zone System was developed for and, technically speaking, only
exists for, B&W photography, the concepts can easily be extended to color.
If you master these concepts, you will not need to bracket _at all_! Your
photos will simply be properly exposed every time. It doesn't matter what
the subject is, what the lighting conditions are, what film or camera you
are using, the exposure will be the best that it can be. Don't get me
wrong - if you are shooting a scene with ten stops difference between the
darkest point and the brightest point and your film has only five stops
latitude, something will have to give, but at least you will know how the
photo will turn out before you even take the picture. You can decide what
portions of the image will have detail and what will be lost in the shadows
or in the highlights.
Ideally, you should use a spot light meter for the measurements, but if you
are able to get close to the subject - which we can with pots - then you can
use a normal hand-held meter. Just don't get so close to the subject that
you shadow it. Also, hold the meter so that it is in line between the
subject and the camera.
I'll see if I can describe the basics briefly (I know - this is already
long).
First, go the above web site, optimize your monitor
(http://www.cicada.com/pub/photo/zs/calibrate.html), and look at the gray
levels of the different zones
(http://www.cicada.com/pub/photo/zs/tables/31.html). Zone V is the
brightness of an 18% gray card and is the basis from which everything else
is judged. Zone IV is a dark gray and is one stop less exposure than Zone V.
Details are clearly visible. Zone III is a darker gray, but with detail
still showing when you look closely. Zone III is two stops less than Zone V.
Zone II is almost black, with detail visible under close examination. Zone
VI is one stop more exposure than Zone V. A general rule is that the
brightness of caucasian skin on a print is about Zone VI. Zone VII is a
detailed white. Zone VIII is white with some detail still evident.
Illuminated snow would often be represented as a Zone VIII.
Knowing this then, we can meter a navy blue pot and realize that it should
_not_ be the same brightness as an 18% gray card, but should be more along
the lines of a Zone IV or III 1/2. So we would subtract 1 to 1 1/2 stops
from the indicated reading to achieve the proper exposure. If we metered a
mostly white pot we would not want that represented as an 18% reflectance,
we would want something more like a Zone VII and would add two stops to the
indicated reading to determine the proper exposure.
You need to meter both the darkest point that you want to show detail as
well as the brightest point that you want to show detail. Ideally, you
"place" the dark area at the zone that you want and adjust the development
to have the bright area "fall" where you want it. If you are dealing with a
print, you get a second chance to manipulate the densities. If you don't
have control of the development, you would look at the two measurements that
you made and choose a compromise to make an exposure that will produce the
best result given your lighting conditions and film.
Color slide film typically has a shorter exposure latitude than either color
print film or B&W film, so the direct correspondence between stops and
density breaks down somewhat, but the concept still applies and you can
recalibrate the zones to whatever your film/camera/meter/processing system
provides.
All this metering and adjusting may sound tedious. The first few times that
you do it, it will take some effort. Things are a lot easier if you are
using your camera's through-the-lens meter so that you don't have to
compensate for filtration or bellows effect. After a little practice you
will find yourself looking at a pot thinking, "I ought to shoot that about a
Zone VI." You take a couple of measurements, compensate the meter reading,
and shoot, knowing that the results will be what you want. Even professional
wildlife photographers, who must deal with unpredictable movements of far
away subjects, are able to use this system.
There is no simplistic approach to determining proper exposure. Even the
most advanced camera metering systems can't possibly understand what _you_
want the picture to look like. Manual metering and a systematic
compensation, such as the Zone System, is still the most effective way to
achieve the proper exposure.
Bruce "I'm sure that clears _everything_ up" Girrell
in rainy northern Michigan where Lynne and I finally got to fire some pots
this weekend. Miserable results the first day. Broke out the OxyProbe. My
burners were _way_ off! Amazingly, the pots turned out much better after
readjusting the atmosphere. Why didn't I do that sooner?
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