"piterengel" <pslaviero RemoveThis @interfree.it> wrote in message
news:ac51fdbf-2d1d-4f35-8850-26a60c31b55b@c4g2000hsg.googlegroups.com...
> Hi, I've had a discussion with a friend of mine about
> darkroom safe
> light.
> Even if on Ilford Multigrade paper box a light brown
> safelight is
> indicated, in my opinion a red safelight works well too.
> Or, better,
> red light is "more universal" than light brown one. Is
> this correct?
> Thanks all
> P.
This is true with some qualification. Modern variable
contrast papers are sensitive to green light was well as red
so a usable safelight should not have much output there. The
Wratten (Kodak) OC, Ilford 905, and similar filters are
designed for use with VC paper, however, they do have some
output in the range the paper is sensitive to so the time
the paper can be exposed to them without fogging is pretty
limited. A red safelight, like the Wratten No.2, has less
output in the green and yellow range so its "safe" for both
VC paper and orthochromatic film, which generally is
sensitive into the yellow as well as green. Some VC papers
recommend a red safelight because they have more extended
green sensitivity than is typical.
The qualifications are that no safelight is completely
safe, that is, all will produce some fogging if the
sensitive material is exposed to the lamp for too long. The
other qualification is that the sensitivity of the eye has
an effect on how bright the safelight must be to be useful.
The dark adapted eye is most sensitive to bluish-green light
and has very poor sensitivity to red light. So, for a given
perceived brightness a greenish amber lamp like the OC will
be greater than a red light with the same actual brightness.
Where the safelight has some residual output at the
wavelengths the paper is sensitive to the lower required
brightness of the amber light may actually make it "safer".
Visual acuity is also color dependant and is better under
green light than red although the acuity of a dark adapted
eye is inferior to the eye in reasonably bright light. This
may not be significant for reasons noted below.
Also, some people just find an amber light to be more
comfortable to work under. As far as judging prints I find
that all safelights distort perception to some degree. I
think this has more to do with brightness than with color
but probably both have an effect. What one must do is to
keep notes on the way prints look under the safelight and
then evaluate them later under white light when they are
dry. After a while you will get some idea of what
differences the light makes. Note that there is always a
difference between a wet and a dry print. For some papers
and surfaces this can be considerable. Generally, both
maximum black and contrast are greater for wet prints.
My point is that since evaluation of a print is going to
be somewhat misleading under the safelight and while it is
wet the differences between safelights is not too
significant, you still have to judge the finished print
under white light.
A further note: B&W printing is often described in a way
that makes it seem that development should be adjusted for
the individual print. I think a better practice is to
develop for a fixed time and adjust exposure according to a
scale established by white light results. While errors in
print exposure can be to some degree compensated by varying
the development time, and while development time may have to
be extended for used developer, the process can be
controlled as much as film development. Because paper is
developed to "completion", that is, to obtain the greatest
black density possible with the paper, the contrast is
pretty much fixed. While there are all sorts of variable
contrast developers and development techniques in the
literature most don't work or have only a very slight
effect: contrast is pretty much built into the paper.
Another caviat, all safelights should be tested
periodically. The filters can fade with time. Both Kodak and
Ilford have effective procedures for testing on their web
sites. I think the Kodak data sheet is K-4. The two
procedures are somewhat different but both accomplish the
same thing so either will do.
--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk RemoveThis @ix.netcom.com
>> Stay informed about: Darkroom safe light 
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