One reason for the amber safelights is their visual effect.
Dark red is safe for nearly any orthochromatic or color blind
emulsion but is hard on the eyes plus the sensitivity of the eye
for red is quite low. Most VC materials are not sensitive in the
yellow spectrum and the light appears much brighter for a given
actual intensity. Now, some VC papers are actually pretty
sensitive in the green/yellow spectrum and the usual Kodak OC
safelight is not really safe for them. These do require a red
light although perhaps not as deep red as orthochromatic film.
For many filter materials one can get a spectral
transmission curve and compare it to the sensitivity curve of the
material you want to handle under it. OTOH, the simple "coin"
test will tell you if the safelight is fogging the material. The
basic rule is there is no such thing as a safe light, any light
will cause fogging under sufficient exposure. Test to see how
bright the light can be without causing fog. You want the
brightest light the material will tolerate to work under.
I agree with the method of using multiple safelights. The
emulsion will be most sensitive before exposure and will begin to
lose some sensitivity once it gets into the developer.
I am not sure what safelight filters are available these
days, used to be easy to get them.
You can always dim a safelight by putting a sheet or more of
brown paper over the filter.
BTW, the use of dark green for panchromatic materials needs a
special technique: it is not really a safelight. The green was
chosen for two reasons: first, many pan materials have a dip in
their spectral sensitivity in the green (T-Max does not) and,
secondly, the dark adapted eye is most sensitive to about this
color of green so a lamp of minimum brightness can be used. Note
that the use of the green light is for brief occasional
inspections of density after development is about half completed.
Most developers (but not all) desensitize the material as
development progresses. What you are looking for is the
transmission density. Hold the film up to the light (not too
close) and hold a finger behind it to compare the developed
density to the finger. you may not see much by reflected light.
Usually, by the time the development is half completed the
anti-flare dye will be decolorized so you can see through the
film. If you try this before the developer has had a chance to
work the film will be opaque by transmitted light and too diffuse
by reflected light to tell much. It is not like working on ortho
or color blind film under a red light although the same method,
i.e. looking at transmission density, is recommended (by Kodak
and others).
I am not much of a fan of development by inspection, usually
only necessary where there is not very good control of exposures
and development.
On 10/7/2021 11:16 AM, Tim Daneliuk (tundra) wrote:
On 10/7/21 11:53 AM, Eddy Willems wrote:
I'm afraid you didn't buy the right filter, certainly not when you want to work
with multigrade photo paper, some yellow light still comes through the filter
I disagree. I use new old stock X-ray processing filters that are deep red
quite happily with VC papers of all kinds.
