Re: (Fwd) Re: Color UV?

[Zoe Paddy Johnson CIRT CSOS <pjohnso@xxxxxxx>]

I posted this yesterday, but when the post came back via the list, it was 
empty so...
Our 1968 Wratten Handbook shows 3 filters labeled 47, 47A and 47B.

The 47 is called dark blue and has the same description Russ gives.  The 
filter transmits light from 350nm thru 530nm, so it is getting much more 
blue than uv.  The old number was C5.

The 47A is called light blue.  It transmits over a broad multi-lobed 
curve from 290 thru 560, with another lobe that extends into the IR 
starting at 680nm.  No old number.

The 47B is again called dark blue.  It transmits from 380 nm thru 500nm.
No old number.

For comparison, the UV pass filter we use, appears black, but you can see 
thru it if you hold it real close to your eye and then look at a light 
bulb, you see a deep maroon glow.  If you put a 301A IR cut filter in 
front of it, you see an even fainter violet glow, so the "maroonish" glow 
is due to the secondary lobe of the filter.  The primary lobe runs from 
305nm thru 400nm.  The secondary lobe starts at 700nm.  This is the 18A.

>From reading the accompanying chart, 9.4% of the light the 47 picks up is 
UV, for the 47A it is 26.4%, the 47B is 4.51% and the 18A is 99.64%.

Geoff has an old spiratone violet filter that gives fascinating effects 
when used on color film to photograph parrots.

ZoeJohnson  


On Sun, 26 Jan 1997, Robert Long wrote:

> 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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