FotoDave@aol.com
Tue, 13 Apr 1999 00:54:02 -0400 (EDT)
In a message dated 99-04-12 20:51:37 EDT, you write:
> With a step wedge you will probably contact print and the result would be
> different than the one enlarged.
You can get projection step wedges which is basically step wedges in 35mm,
120, or 4x5 format. You would then do the tests with enlargement rather than
contact; or if you have more than one contact (regular, long strip) step
wedge, you can use 2 or 3 in your negative carrier and do the enlargement
tests.
And of course, if your enlarger is diffuser type, the difference between
enlargement and contact would be very small, if at all detectable.
> I don't know if it makes sense but when I
> remove the negative from the carrier I will also remove base fog, so the
> light striking the film in the easel is much stronger than the light
passing thru
> any no image part of the film.
Yes, but isn't the whole point of using step wedge that once you have
obtained the "data," you can adjust your exposure accordingly? For example,
since you know the density of your base+fog, you can adjust your flash
exposure accordingly.
> When you contact print you will not have this
> effect so having a higher flash %.Is anyone else getting short flashes too?
I personally think that the recommended flash is too short for precise
control. I do use flashing in some special applications (not reversal), and I
put special effort in having long flash time for control reason. You can
prolong flash time by increasing the height of enlarger head, closing f stop,
using neutral density filter, or use a separate light for flashing (e.g. a
low light directed toward the ceiling).
While I don't do reversal processing myself, I think it is a nice idea
especially for anyone wanting a quick, direct negative without much
manipulation (such as masking). However, it seems like the sensitometric
principles behind it is not clearly understood. It is actually simple but
difficult to explain in words alone. My recommendation is that rather than
testing it in positive and then multiply by a factor (this factor actually
depends on the density range of your original negative), you arrange your
test exposures so that in a piece of film, you have the 2x, 3x, 4x, ....
exposure. You pick the one that gives you the best shadows. Then you use
flash to control the highligh and the final density range.
As I mentioned in a previous message, if you can obtain the perfect, desired
shadow but no matter how much or little you flash, you still cannot get the
right highlights, the density range of your negative exceeds the exposure
range of the lith film. You can't do much about it. It is not a shortcoming
of the process. Rather, it is the characteristic of lith film. In that case,
you could use a camera negative or use masking.
But one should really do a step wedge test with base exposure covering the
toe and shoulder, then with the same base exposure, do a range of flashing
test, then everything will become perfectly clear.
Dave S
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