Re: (Fwd) Re: Color UV?

[boblong@xxxxxxxxxxx (Robert Long)]

On Sun, 26 Jan 1997 01:37:21 GMT, Russ Rosener wrote:

|Speaking of Ultra Violet photography, I found an old Wratten # 47 filter
|in my filter box last night. It's a deep indigo blue, so I wonder if =
this
|is some kind of Ultra violet filter which could be used to take images =
in
|the UV spectrum?

The Wratten 47 actually was listed as tricolor blue and was intended
for use in making color separations.  (There were two versions: the 47
for use in dye-transfer work and the 47B for graphic-arts separations,
but I don't know what the difference was.)  In its booklet "Infrared
and Ultraviolet Photography" (Sixth--evidently 1955--edition, 1959
printing), Kodak discusses ultraviolet-pass filters but includes no
Wratten types, which I believe were all constructed with regular
(UV-inhibiting) glass.  The recommended filters are all in the Corning
5xxx series.

Other manufacturers made filters that looked like the Wratten 47 (mine
is from Spiratone) and sold them for times when the photographer wants
to maximize the effect of atmospheric haze in b&w photography.  A
biproduct of this use is a general reduction in contrast (just as a
Wratten 25 filter will increase contrast even with standard
panchromatic films), but Spiratone labeled its blue filter as a
"Contrast Filter."  Kodak also mentioned "contrast effects" for the 47
without saying precisely what sort.  So the spiel I was given when I
bought the filter--and my *very* limited experience in using it--may
be misleading, and perhaps it does, indeed, increase apparent contrast
in some circumstances.  Because shadows are rich in blues and weak in
reds, however, the reduced-contrast paradigm makes sense.

Bob Long
(boblong@xxxxxxxxxxx)

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