From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Newsgroups: rec.photo
Subject: Re: Viewing Filters (long)
Date: 25 Jan 1993 23:33:35 GMT
Organization: Lawrence Berkeley Laboratory, California
Distribution: world
NNTP-Posting-Host: 131.243.192.10

>> For years I have seen "viewing filters" listed in catalogs (they all
>> seem to sell the same one made by Peak).  One catalog I have states that
>> viewing filters will "render tonal values as they will be reproduced by
>> film".

[stuff deleted]

>Someone whose head is sufficiently capacious to hold the spectral
>responses of the Wrattens will no doubt be able to tell you what colour
>a #90 is.  Until then, I might speculate that this is the purple one I
>have...  The ones I see in catalogues are mostly a muddy green colour. 
>However, I have no particular reason to believe that one is right and
>the other is wrong.  The purple one seems to work for me.
>
>   -- Ian
>
>P.S.  I would have mailed rather than posted, but it seems to me I have
>seen this question before.  (Yet another) one for the FAQ list?

Yeah, I've seen it posted before too but I can't seem to find it now.
I don't know what the spectral response is but I'm sure it's in the
CRC handbook.  I've written down a few of the filter numbers from the
CRC Handbook of Chemistry and Physics and from other places:

------------------------------------------------------------------------


filter	color	                     use

colorless
UV(0)	none	absorbs UV
0	clear	thickness compensation
1		absorbs UV < 360nm
1A	pale pnk skylight filter
1B	lt. pink (skylight) cuts blue cast in shade and distance, absorbs UV

yellows
2A	pale yel	UV 405 nm
2B	pl yel	absorbs UV 390 nm
2E	pl yel	absorbs UV
3	lt yel
4	lt yel	CCC - corrects outdoor scenes for panchromatic film
6	lt yel	(aka K1) partial correction for outdoors
8	yel	(aka K2) full correction outdoors for Type B panchromatic film
9	dp yel
11	yl-grn	(aka X1) corrects tungsten light for Type B film
12	dp yel	minus blue - haze cutting for aerial photography
13	yel-grn	(aka X2) corrects tungsten light for Type C panchromatic film
15 	dp yel	(aka G) contrast control in aerial IR photography
16	yel-org	blue absorbtion
18A		transmits UV and IR only

oranges and reds
21 	org	blue and blue-green absorbtion
22	dp org	yellow-orange (mercury yellow) increase contrast in blue 
		preparations for microscopy
23A	lt red	contrast effects
24	red	for two-color photography
25	red	(aka A) for tri-color separation, high contrast effect, 
                aerial IR haze
		two-color general viewing
26 	red	stereo red
29	dp red	high contrast, tungsten projection of tri-color, red sep. in 
                fluor. process

magentas and violets
30		green absorbtion
31		green absorbtion
32	magen	minus green
33		strong green absorbtion
34A 	violet	blue separation in fluorescence process
35		contrast in microscopy
36	dk violet

blues and blue-greens
38		red absorbtion
38A	Blue	red absorbtion, increasing contrast in visual microscopy
39		contrast control in printing motion pictures
40 	green  	two-color photography
44	lt blu-grn minus red, two-color general viewing
44A	lt blu-grn minus red
45		contrast in microscopy
46		blue projection
47	blue	direct color separation, tungsten tri-color projection
47A	lt blue
47B	dp blu	tri-color separation form transparencies
48		green and red absorbtion
48A		green and red absorbtion
49		dark blue
50		very dark blue - mercury violet

greens
52	lt grn
53		middle green
54		very dark green
55		stereo green
56 		very light green
57		green for two-color photography
57A	lt grn
58	grn	tri-color green for separations, contrast in photog & microscopy
59 		green for tri-color projection
59A		very light green
60 		green for tungsten two-color photography
61 	dp grn	grn tri-color sep, tungsten projection
64		red absorbtion
65		red absorbtion
66		contrast effects in microscopy & medical photography
67A		red absorbtion   Two-color projection

narrow band
70 	dk red	IR photography 		676 nm
72B	dk or-yel			605 nm
73	dk yel-grn          		575 nm
74	dk grn	mercury green   	539 nm
75	dk blu-grn          		488 nm
76	dk vio	(compound filter)   	449 nm

Hg line filters
77		transmits 546 nm mercury line.  glass plus gelatin   580 nm
77A		transmits 546 nm mercury line.  glass plus gelatin   582 nm

photometrics
78	bluish		photometric filter (visual)
78AA	bluish		photometric filter (visual)
78A	bluish		photometric filter (visual)
78B	bluish		photometric filter (visual)
78C	bluish		photometric filter (visual)
86	amber   	photometric filter (visual)
86A	amber   	photometric filter (visual)
86B	amber   	photometric filter (visual)
86C	amber   	photometric filter (visual)

light balancing
80A  blue  color correction for daylight film (5500) under 3200K (studio) lamps
80B  blue  color correction for daylight film (5500) under 3400K (photo) lamps
80C  blue  color cor. for daylight film (5500) under 3800K (clear flash) lamps
81  amber  warming -100K
81A amber  color correction for Type B tungsten film under 3400K (photo) lamps
	   warming -200K
81B amber  to remove blue cast in shaded daylight
	   warming -300K
81C amber  to remove blue cast in cloudy/rainy weather; Kodachrome Type A with
           flash;  warming -400K
81D amber  Kodachrome Type A with flash; warming -500K
81EF amber Ektachrome Type B with flash; warming -650K
82   blue  cooling +100K
82A  blue  color correction for Type A tungsten film under 3200K (studio) lamps
	   cooling +200K
82B  blue  color correction for Type B tungsten film under 2900K (100w incand.)
           cooling +300K
82C  blue  to remove reddish cast in early morning or late afternoon
	   cooling +400K
83  amber  16mm commercial Kodachrome in daylight
85 orange  color correction for Type A tungsten film in daylight (5500K->3400K)
85B orange color correction for Type B tungsten film in daylight (5500K->3200K)
85C amber  converts 5500K (daylight) to 3800K lighting

miscellaneous
79	photographic sensistometry
87	for infrared photography; absorbs visual   	770nm ->
87C	absorbs visual, transmits IR   			830nm ->
88A	for infrared photography; absorbs visual   	740nm ->
89B	for infrared photography    			700nm ->
90	monochrome viewing (narrow-band for viewing scene brightness);
	about 570->590 nm; 10% luminous transmittance
96	neutral filter for controlling luminance; 9% luminous transmittance
97	dichroic absorption
102	correction filter for Barrier-layer cell
106	correction filter for S-4 type photocell
FL-day  purple	converts "daylight" fluorescent light for daylight film
FL-W    purple	converts "white" fluorescent light for daylight film
K2      yellow	improves contrast in B&W; absorbs UV and part of violet
G       orange  greatly improves contrast in B&W; absorbs UV and part 
                of blue-green
25A 	red	strongest B&W contrast; absorbs UV and part of yellow; 
		"night filter"
		also used as a color separation filter with #47 blue and 
		#58 green
X0	yel-grn	natural rendition of skin and lips of female models    B&W?
X1	green	Absorbs more red than X0, good for green trees       B&W?

Data on a very few narrower band filters:
Filter no.  low wavelength  high wavelength  domin. wl      lum. transm. %

Color separation filters:
47 blu		400		475		464		 2.8
58 grn		490		600		540		23.7
25A red		590		700		615		14

Narrow band filters:
76		400		470		449		0.046
75		460		530		488		1.3
74		510		570		539		4.0
73		560		600		575		1.3
72B		590		640		605		0.74
70		660		700		676		0.31

This data is from the CRC handbook.  Much more data is available in the CRC.