Liam Lawless (lawless@vignette.freeserve.co.uk)
Wed, 14 Apr 1999 01:12:29 +0100
Hi Ken,
In the time it's taken me to get a reply together you've had a number of
answers that say pretty much all I'd have done, but I'd like to add that it
was not a good idea to list flash times as percentages of the main exposure
because, as I soon found out, the flash necessary to achieve a given maximum
density can vary greatly with the densities of original negatives. The
figures were only intended as a rough guide, but they seem to have proved
misleading.
You report that you found a factor of 3X better than the recommended 6X with
your pyro-developed original, and my guess is that your film/developer
combination does not give a strong pyro stain (in which case it would
probably be better to treat it as a straight silver neg); my advice was
based on Tri-X/PMK which stains quite heavily. But, again, the best choice
of exposure factor is also influenced by the densities of your original. A
low factor maximises shadow detail (and so is chosen when shadow detail is
weak in the original), but also gives lower contrast.
>My 30 second exposure (f 32) was showing a max density of 4.25 with no
>flash, 3.42 with 1 sec flash, 1.45 with a 2 second flash, .91 with a 4 sec
>flash, .64 with a 6 second flash and .56 with an 8 second flash.
>
>This means that my 3.0 negative would use about a 3% flash and 1.9 will be
>around 1.5(?) seconds or ~5% and my 1.5 negative would be ~7% compared to
>articles' 15%, 30% and 45%!
>
You say you used a 30-second base exposure (which, with the 3X factor, means
your normal time would have been 10 seconds). Someone is borrowing my P-F
at the moment, but I'm reasonably sure I said somewhere in the article that
a flash time between 10 and 50 percent of the NORMAL time will usually cover
the range of useful densities. For a normal exposure of 10 seconds, this
would indicate a flash between 1 second and 5 seconds, which would give you
a choice of maximum densities between 3.42 and (roughly) 0.8. (Sounds like
you've confused the normal and base times, though without checking I can't
say whether I told you wrong in the article!)
It is true that the flash time is critical and can be very short, and you
will find that it is more critical as it is shorter (i.e. when aiming for
high maximum density). Judy's suggestion of a separate flashing light is an
excellent one, but I wanted, originally, to make the method as simple as
possible, and what could be simpler than using the enlarger to flash, at the
same aperture as used for the base exposure? Stopping down probably isn't
an option as you were already working at f/32, but cutting down the
intensity of the flashing light does permit more control by increasing flash
times. Since writing the article, I have wired my (mains-powered) enlarger
through a dimmer switch for this reason, though another way would be to use
neutral density or variable-contrast printing filters under the lens. Since
the flash time is established by test strip, it is not even necessary to
know the filter factor of whatever you use (though the 10 to 50 percent of
normal exposure rule would no longer work).
A big, unexpected advantage of my dimmer switch is that with it set so that
I can work at f/11, my enlarged negs are significantly sharper and brighter
than they were at f/32. The reason for this is that lenses are generally
reckoned to perform best a stop or two down from their maximum aperture
(mine is a f/5.6 Componon), something I had not previously considered.
Well, you don't sound too disappointed with the method, though I'm sorry
you've wasted a whole box of film. APH and APHS are roughly two stops
faster than bromide papers, which means that your initial exposure test
should be based on a quarter of the time you would give if printing on a
paper like Ilford Multigrade. But there is a short cut. Base exposure
times are not really very critical, so if you have an enlarging exposure
meter (e.g. the Ilford EM-10) you can use it to obtain a sufficiently
accurate estimate of the normal exposure, and apply the factor to the time
obtained. The instructions supplied with such instruments usually say to
calibrate them for the brightest highlight tone, but I get better results
calibrating for the deepest shadows.
Hope this is some help, and thanks to everyone else who's responded. I'm
still learning too.
Liam
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:30