FotoDave@aol.com
Mon, 18 Jan 1999 22:12:19 -0500 (EST)
In a message dated 99-01-14 15:59:11 EST, you write:
> Second, I've been printing wedges like crazy ....
Absolutely beautiful! excellent! wonderful! smart! intelligent!
> Step ten is the beginning of the highlights,
> and I have decent seperation up to step 5, but steps 5-2 show very little
> seperation, with step 1 going quite a bit darker. Does this mean that I
> should consider step 5 to be the end of the wedge? What about the great
> 'black' at step 1 - is this just tantalizing me with the impossible? In
> general, I see this often - 4 steps or so of color, and another 4 with
> weak seperation and the last one or two with more seperation - what gives?
I know what you are after. You want that deep, rich, thick, velvety,
beautiful, gouachy black! :) Rather ambitious, but since you have printed
step tablet like crazy and have a good sense of sensitometry, I am sure you
can get it.
This is actually a common problem in photographic emulsion, including silver
gelatine emulsion. If you consider the nice separation region (print paper
typically uses 90% of Dmax in calculation), the curve is approximately linear
(as most books will tell you), but if you include the deepest black, there is
a shoulder, and there is a long long shoulder for gum.
Basically you want to increase the contrast of shadows but retain the
separation region.
There are a few methods that you can use to get that black:
1. Single-Negative
Increase the contrast to increase the separation of step 1 to 5 in your
example. This will make the contrast of your negative super high, so you will
have to multiple coat (at least 3 if you do the calculation) and print with
different contrasts (higher for shadows, pretty flat for highlights).
If you carefully calculate and make a lot of tests (w/ your step tablet), you
might be able to reduce the printing to 2 coats.
2. Double-Negative
Use a high contrast negative and a low-contrast negative. Even if you use lith
film, since the exposure range of the film is about 7-8 steps, you can only
use 2 film and 2 coats as opposed to 3 coats as required in #3.
3. Masking Method
Use a mask to control the negative so that shadow contrast is increased but
highlight is lowered. You would still probably need 2 coats, so it doesn't
seem to be much different from #2. However, this might be preferred if, say,
you make a 4x5 positive and mask and then make the final enlarged negative.
In all cases, if you are familiar with sensitometry, it is not really that
hard to calibrate a system. I am omitting as much details as I can. If you
have any specific question, feel free to contact me off list because sometimes
I get complains when I give details.
Dave
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