I hope I won't confuse you even more. Densitometry and sensitometry can be a
little bit confusing at first, but once you get it in the system, you get it.
You will feel that you can throw away all the books about them and zone
system. (Zone system is not a separate system. It is, technically speaking,
simply a specific application of the two systems mentioned).
In a message dated 98-01-14 15:08:01 EST, cor@ruly46.medfac.leidenuniv.nl
writes:
<< ...but is there not an absolute value/density attached to a graycard (
I mean, when one makes a photograph of a graycard, it's properly exposed,
the film is correctly processed, when one reads the density (assuming a
good calibrated densitometer, one should get an absolute, fixed value
of..?)
Yes and no. Of course a gray card has a fixed density value, but the meaning
of density in itself is *relative.* Remember the definition of density? It is
the log of opacity, which is the inverse of reflectance or transmittance. So a
gray card simply means it is a card that reflect back 18% of light that shines
on it. This is *relative* because it does not tell you how light or how dark
the card is, it simply tells you that it will refelct back 18% of lights that
falls on it.
The reason that people in photography have used it more or less as an absolute
value is because within this specific application, it is assumed that
everything (camera, shutter, apperture, light meter, film, developer,
enlarger, and paper) works in a specific manner; and in zone system, Adams had
worked out a way to use it so that it will work for normal paper. It does not
have to be that way.
In zone placement, just for an example, we open up or close down the lens
opening. Note that technically speaking, this is equivalent to say that you
use a lighter card or a darker card but treat it as the gray card. You might
not grasp this completely, but it again shows that *gray* is relative.
When you deal with special film, or special developer, or the not-so-normal
situation, you need to be able to calibrate the system differently. In order
to do that, however, you need to understand why it works in the first place
and how it works technically in additional to understanding, for example, that
you have to place zone I to 0.10 + b + f and develop zone VIII to this value
or that value.
>> Maybe I am fussing to much about these details, of course its the produced
image that counts, wheter it's from a lousy exposed neg. for that
particulaer process or from a perfect one. It's just that I like to test a
bit, to give me more insight in the matter, without hopefully becoming a
slave of eternal testing, but at the and be able to concentrate only on
the subject when I photograph (but what was the subject....)
>>
You are close, so you can go back and forth. If things start to get too
confusing, forget it for a while and concentrate on producing good image; but
don't throw it away completely. Read about it, think about it, ask and discuss
about it; and I am sure one day you will get it completely. Then it will
enable you to create good images easier and more repeatible. Densitometry is
just a tool, but it is a beautiful tool!
Sincerely,
Dave
PS: I talked too much and forgot about your original question. If you have
*very specific* question, you can email me (on or off list), and I will try to
make suggestion. But remember densitometry is a complete system, so it is hard
to say something like measure step 5 of Stouffer step table, and develop so
that its density is .7 or whatever. One has to view and know the complete
cycle.