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    FAQ or Answers to Frequently Asked Questions                  Section 21
    This is a file containing answers, tips, hints and guidelines associated 
    with recurring  questions asked by photographers.   If you would like to 
    add a tidbit of knowledge to  this list just send it to   ANDPPH@rit.edu 
    who will gladly add it to this collection. 
                     These files are available in SECTIONS. 
              This is Section 21 and its contents are listed below.
    21.01  -< A DOF program written in C FYI >-
    21.02  -< Polaroid batteries and accessories >-
    21.03  -< Infrared Ektachrome Processing in E-6 chemicals >-
    21.04  -< New f# when using bellows extension >-
    21.05  -< Data on Wratten Filters by the Numbers >-
    21.06  -< CHEAP IR Filters - experimental quality >- 
    21.07  -< UV and IR Technique Basics >-
    21.08  -< Solarization Tip >-
    21.09  -< Create-a-Print used for B&W printing >- 
    21.10  -< Decoding De DX Code >- 
    21.11  -< IR Ektachrome Processing in cool E6 chemicals >-

Note 21.01            -< A DOF program written in C FYI >-
From: bjthomas@cisco.com (Bill J. Thomas)
Subject: depth of field c code
Organization: cisco Systems
the following is a Depth of Field program written in C 


 enter focal length in mm's 135
 enter Y for 35 mm N for roll or sheet film Y/N? n
 enter focal length in mm's for depth of field f ratio scale 135
 Enter plot scale increment e.g., 0.4 now 0.4

    Feet     f3.5       f4     f5.6       f8      f11      f16     f22     f32
f scale     0.130    0.148    0.207    0.296    0.407    0.593   0.815   1.185

 Focus in Feet   4.921 Scale is    9.000
 Focus in Feet   5.150 Scale is    8.600
 Focus in Feet   5.401 Scale is    8.200
 Focus in Feet   5.678 Scale is    7.800
 Focus in Feet   5.985 Scale is    7.400
 Focus in Feet   6.327 Scale is    7.000
 Focus in Feet   6.711 Scale is    6.600
 Focus in Feet   7.144 Scale is    6.200
 Focus in Feet   7.636 Scale is    5.800
 Focus in Feet   8.202 Scale is    5.400
 Focus in Feet   8.858 Scale is    5.000
 Focus in Feet   9.629 Scale is    4.600
 Focus in Feet  10.546 Scale is    4.200
 Focus in Feet  11.656 Scale is    3.800
 Focus in Feet  13.027 Scale is    3.400
 Focus in Feet  14.764 Scale is    3.000
 Focus in Feet  17.035 Scale is    2.600
 Focus in Feet  20.132 Scale is    2.200
 Focus in Feet  24.606 Scale is    1.800
 Focus in Feet  31.637 Scale is    1.400
 Focus in Feet  44.291 Scale is    1.000
 Focus in Feet  73.819 Scale is    0.600
 Focus in Feet 221.457 Scale is    0.200
 Compute Depth of Field Table Y/N? n

 End computations ? (Y/N) n

 enter focal length in mm's 90
 enter Y for 35 mm N for roll or sheet film Y/N? n
 enter focal length in mm's for depth of field f ratio scale 135

    Feet   f3.5     f4   f5.6     f8    f11    f16    f22    f32
f scale   0.292  0.333  0.467  0.667  0.917  1.333  1.833  2.667

=====================plot depth of field slide rule=============
Lay out the "DISTANCE SCALE" using the numbers from the Focus in Feet
	 Draw a vertical line (DISTANCE SCALE).
	 At the top print the symbol for infinity.
	 Next at 0.200 inches (2/10'ths of an inch) print 221.457 feet.
	 Continue with the rest.
	 At the bottom at 9.000 inches from the top print 4.921 feet.
Lay out the 135 mm lens "DEPTH of FIELD SCALE" using the numbers
from the 135 mm "f scale" display.
	Draw a horizontal line with an arrow at the right end (FOCUS ARROW).
	Draw a vertical line through the horizontal "FOCUS ARROW LINE".
	On the vertical line print f11 "0.407" inches above and below
	Repeat the above for the rest of the numbers in the "f scale"
 USAGE: Align the vertical line of the "DEPTH of FIELD SCALE" with the
        "DISTANCE SCALE".  Set the "FOCUS ARROW" at the focus distance
        on the "DISTANCE SCALE" (say 17 feet).  Now for a given lens
        opening (say f11) read off the distance both before and after
	the focus distance (14.7ft & 20.2ft). Everything between these
	distances will be in focus (based on the "circle of confusion"
	built into the code based on your answer to "enter Y for 35 mm
	N for roll or sheet film Y/N?").
Lay out the 90 mm lens "DEPTH of FIELD SCALE" using the numbers
from the 90 mm's "f scale" display as was done for the 135 mm lens.
By running a series of different lens lengths less than in this case 135 mm,
you can construct a "DEPTH of FIELD SCALE" like the ones found on many
zoom lenses.



float F, H, u, c, dn, df, Hu, F_scale, H_scale;
char type_c;
#define MAX_u 1000
float u_range[MAX_u];
float v_delta;
float v_ratio;
#define max_f  8
short max_u;
#define TRUE 1
float temp[max_f];
short i, j;
/*float f_range[] = {3.5, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0, 32.0};*/
float f_range[max_f];

f_range[0] = 3.5;
f_range[1] = 4.0;
f_range[2] = 5.6;
f_range[3] = 8.0;
f_range[4] = 11.0;
f_range[5] = 16.0;
f_range[6] = 22.0;
f_range[7] = 32.0;

    printf("\n Lense Depth of Field Calculations");
    printf("\n 		Copyright (C) 1992. ");
    printf("\n 		All rights reserved ");
    printf("\n           Bill Thomas ");
    printf("\n           43559 Southerland Way ");
    printf("\n           Fremont, CA 94539 \n");

	printf("\n enter focal length in mm's ");
	scanf("%f", &F);
	if(F < 0.0) exit(0);
	printf(" enter Y for 35 mm N for roll or sheet film Y/N? ");
	scanf("%s", &type_c);
	printf(" enter focal length in mm's for DOF f ratio scale ");
	scanf("%f", &F_scale);
	if(F > F_scale) {
	printf("\n f ration length can't be less than focal length \n");
	F *= 0.03937;
	F_scale *= 0.03937;
	if(type_c == 'Y' || type_c == 'y')
		c = 0.001; /*for 35 mm*/
	else {
		if(type_c != 'N' && type_c != 'n'){
			printf("\n ***ERROR*** enter Y or N!!! ");
		c = 0.0019685; /*roll or sheet film*/
	H_scale = F_scale/F;

/*compute feet depth scale so as to be plotted at v_delta increments */
	v_delta = 0.4;
	if(F_scale == F){
	    printf(" Enter plot scale increment e.g., 0.4 now ");
	    scanf("%f", &v_delta);
	v_ratio = 9.0;
	i = -1;
	while(i++ < MAX_u && v_ratio > 0.00001){
		u_range[i] = F_scale/(v_ratio*12)*100;
                v_ratio -= v_delta;
	max_u = i;

	printf("\n\n  Feet  f3.5   f4  f5.6   f8  f11  f16  f22   f32");
	printf("\nf scale ");
	for(j = 0; j < max_f; j++){
		H = F*F/(f_range[j]*c);
		/*see v_ratio computation below*/
		v_ratio = F/H*100*H_scale;
		printf(" %8.3f",v_ratio);
	if(F_scale == F){
		for(i = 0; i < max_u; i++){
			u = u_range[i];
			/*m = F/(u*12); */
			/*v = F*(1 + m);*/ /*lens formula*/
			/*v_ratio = (v/F - 1 )*10; */
			v_ratio = F/(u*12)*100;
		printf("\n Focus in Feet %7.3f Scale is %8.3f ", u, v_ratio);
	printf("\n Compute Depth of Field Table Y/N? ");
	scanf("%s", &type_c);
	if(type_c == 'N' || type_c == 'n')goto EndTableComp;

	printf("\f \n  f3.5    f4   f5.6    f8   f11   f16   f22   f32");
	printf("\n   FOCUS");
	for(j = 0; j < max_f; j++){
		H = F*F/(f_range[j]*c);
		printf(" %8.1f", H/12);
	printf("\n        ");
	for(j = 0; j < max_f; j++)
		printf(" infinity");
	for(i = 0; i < max_u; i++){
		u = u_range[i];
		printf("\n %7.1f", u);
		u *= 12;
		for(j = 0; j < max_f; j++){
			H = F*F/(f_range[j]*c);
			Hu = H*u;
			dn = Hu/(H+u);
			temp[j] = df = Hu/(H-u);
			if(dn < 0.0)
				printf(" infinity");
				printf(" %8.1f", dn/12.0);
		}/*end of for(j */
		printf("\n        ");
		for(j = 0; j < max_f; j++){
			if(temp[j] < 0.0)
				printf(" infinity");
				printf(" %8.1f", temp[j]/12.0);
		}/*end of for(j */
	}/*end of for(i */
	printf("\n\n End computations ? (Y/N) ");
	scanf("%s", &type_c);
	if(type_c == 'Y' || type_c == 'y')
    }/*end while(1) */
Note 21.02          -< Polaroid batteries and accessories >-
Are you looking for batteries to power up your old Polaroid camera? Do you need
accessories?  Then the  FREE  catalog of the following outfit may interest you.

                                Graphic Center
                                P.O. Box 818
                                Ventura, CA  93002

They carry batteries and various accessories. They also convert Polaroid 110A/B
to use standard pack film.  They also carry refurbished plastic and  metal pack
film cameras, electronic flashes designed to fit 100-450 seies cameras, EE-100,
Reporter, and others.  Interesting  accessories include PC-flash adapter cords,
cold clips, filters, cable releases,  closeup kits, portrait kits, and filters.

As for batteries, the No. 532, are $7 each., the 4v No.531 batteries are $7.75.

Note 21.03    -< Infrared Ektachrome Processing in E-6 chemicals >-
                    Ektachrome Infrared processing in E-6

The simplest information on E-6 processing of film intended for E-4 was in 
Darkroom & Creative Camera Techniques magazine, Nov/Dec 1989, page 2. They 
had previously tried processing E-4 film in E-6 chemistry, but at 70F. This 
took a lot of time and the results were questionable. They then recommended 
using a prehardener and neutralizer before the first developer (such as is 
used in E-4), and then doing the E-6 process as usual at 85F.  There hasn't 
been any follow-up comment about this since last year in the magazine. The
formulas below should work adequately.

         E-4 Prehardener
                Water			800 mL
          	Sodium Sulfate		140 g
         	Formaldehyde 38%	 30 mL
	        Potassium Bromide 	 16 g
	        Water to make		  1 L

         E-4 Neutralizer
           	Water			800 mL
	        Hydroxylamine Sulfate	 18 g
	        Potassium Bromide	 20 g
	        Sodium Acetate		  7 g
	        Glacial Acetic Acid	  7 mL
	        Sodium Sulfate		 50 g
	        Water to make		  1 L

         These two solutions may be reused.

Most of the chemicals should be available from: Lauder Photographic, 2650B
Mercantile Dr. Rancho Cordova, CA 95670, 916-638-1225,Zone V, Stage Rd, S. 
Strafford VT 05070, 802-765-4508,  Tri-Ess Sciences, 1020 W. Chestnut St., 
Burbank, CA 91506, 213-245-7685. Rapid Fixer should be available from your 
photo dealer. Formaldehyde is available at most any drug store.

         Schedule at 85F:
	        Prehardener	3 min
	        Neutralizer	1 min
         First Developer and remaining steps per standard E-6
	 directions for a processing temperature of 85F.

The E-6 kit recommended in the article was the Kodak E-6 Hobby Pak Kit.

Obviously, these aren't official E-4 formulas, but they should work OK.  The 
biggest problem with E-4 film is that the emulsion isn't prehardened, and it 
gets too soft at normal E-6 temperature (100F). There possibly could be some
color shift, but I would guess if you are wanting to do Ektachrome Infrared 
how would you know a color shift if you saw it??? :)

I hope that this information works for you.  

Ron Speirs, Evans & Sutherland Computer Corp., Salt Lake City, UT
Note 21.04          -< New f# when using bellows extension >=
                 How to adjust for bellows extension factor/stops

It's actually pretty easy to do the arithmetic for this computation in your
head.  The effective  f-stop is simply the marked f-stop times the ratio of
lens-to-film distance (bellows extension) to focal length.

For example, say I have  my handy Schneider 210 mounted up,  and I'm taking a
picture of something at a magnification of 1:1, and I need to set the lens to
f/22 to get everything adequately sharp.  The lens-film distance according to
the tape will be  420mm,  focal length is 210mm,  f-stop is 22.  My effective
f-stop will be 22 x 420 / 210 = 44.  Call it f/45 and dial that into the meter. 
That's all there is to it.

This formula provides an additional benefit - you can calculate a magnification
or distance for which you needn't bother getting out the tape measure.

If 1/6 stop is the  largest  error  you find  tolerable,  that means  that the
lens-film distance/focal length ratio must be 7/6 or less.  Plugging that into
the formula for focal length (fl), lens-film distance (d_lf) and lens-object
distance (d_lo), 

1/fl = 1/d_lf + 1/d_lo

1/fl = 1/(7/6*fl) + 1/d_lo

d_lo = 7*fl

which means if you are more than 7 focal lengths  away from your subject, your
underexposure due to ignoring bellows extension will be less than 1/6 stop. If
you're willing to go to  1/3 stop error, 4 focal lengths is the threshold.  In
general, if you are willing to set your  error threshold at "err" f-stops, the
nearest you can get to your subject without compensating for bellows extension
is  (1+err)/err  focal lengths.  In the case of my 210mm (aka 8 1/4") lens, if
I'm making  life difficult for myself  by using color transparency film, and I
think I can meter things  accurately enough  that 1/3 stop accuracy is crucial
(don't I wish!)  I can see that if I'm closer than  about 3 feet I need to get
out that tape measure.  

Fortunately, since I mostly shoot b&w, and more often than not I'm doing
landscapes, I can see from the formula that I don't have to worry much about
the fact that I lost my tape measure a few months ago :-)


From: whp4@Csli.Stanford.EDU (Bill Palmer)
Organization: Stanford University CSLI
Note 21.05        -< Data on Wratten Filters by the Numbers >
    This is a listing of Wratten Filters by number, their color and
    applications. It was compiled from the  CRC Handbook where more
    filters and additional charactristics are also listed.
number  color    use

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

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

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

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

79	photographic sensitometry
87	for infrared photography; IR   770nm ->
87C	absorbs visual, transmits IR   830nm ->
88A	for infrared photography; IR   740nm ->
89B	for infrared photography; IR   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 l	   high l	 domin. l      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	.046
75	460	530	488	1.3
74	510	570	539	4.0
73	560	600	575	1.3
72B	590	640	605	.74
70	660	700	676	0.31

     This file was found in the photo-3D FTP-able archives at csg.lbl.gov.
Note 21.06        -< CHEAP IR Filters - experimental quality >- 
In case you did not know and might benefit from this information I had
some filters often used for Infrared photography, along with some unexposed
but developed Ektachrome sheet film, characterized with a spectrophotometer.
The films were obviously visually quite opaque. Especially if you stacked two
of these. It turns out that the dyes that make up the color layers in this
film (and I suspect all color films) are visually opaque but IR TRANSPARENT!
This means they can be used as cheap makeshift IR filters, especially to cover
a flash source to make unobtrusive flash photos by IR illumination. This info
is not totally new as I had already seen such curves at RMIT in Melbourne,
Australia, where I spent my summer vacation a couple of years ago. I also used
one and two layers of Ektachrome film as a filter in front of my camera's lens
and the images were not totally fuzzy and unusable. They had, in fact, a visual
quality all their own which you may (or may not) like if and when you
experiment in a similar fashion.                          andy - andpph@ritvax
   3.0|.........    ..........    ....... -------
      |         \__/         :\__/       \    ;  |       :  Wratten #25 (red)
      |                      :            \   ;   |
      |                      :             \  ;    |     ;  Wratten #87 (IR)
D     |                       :             \  ;   |
E  2.0|      approximate      :              \ ;    |    \  1 layer  Ektachrome
N     | Density vs Wavelength :                \;    |
S     |          for          :                 \    |   |  2 layers Ektachrome
I     | 2 Wratten Filters and :                  ;\   |
Y     | Ektachrome Sheet Film :                  ; \   |
   1.0| unexposed & developed  :                  ;  \  |
      |                        :                   ;  \  |
      |                        :                     ;  \  |
      |                        :                       ; \  '- ________
      |                         '.............>           ;-...........
     400          500          600           700          800          900
                            wavelength (nanometers) 

Note 21.07              -< UV and IR Technique Basics >-

                            by Andrew Davidhazy
                   Imaging and Photographic Technology
                    Rochester Institute of Technology

A large part of the spectrum and its relationship to the world around us is
invisible because we are limited to seeing electromagnetic wavelengths which
extend only from those characteristic of violet-blues to those of the deep
reds. Photographic materials can extend our vision, especially when aided by
special light sources and various filters. The proper use of film, lights,
filters, exposure techniques and specific applications of the four basic
methods of photographing the invisible spectrum are discussed below.

The premise for photographing by REFLECTED ULTRAVIOLET or REFLECTED INFRARED
radiation is that we desire to "see" the interaction, by way of reflected
energy from our particular subject, of UV or IR rays as compared to the effect
on the same subject of visible light rays. The hope is that the subject may
appear differently by these rays than it does by "white" light or than it would
appear if seen through colored filters.

An analogy for the reason to apply these techniques is the lengths to which we
go to render a blue sky dark on a B&W print to contrast it against the white
clouds. This, of course, is accomplished by placing a yellow or red
(complementary colors to blue and cyan, the color of the sky) filter over the
camera lens. The filter does not allow the sky color wavelengths to pass on to
the film and thus the sky is rendered clear on the negative and dark on the
print. The point is that we can distinguish between two subjects of similar
tone, the sky and the clouds in this instance, but different color by filtering
out one of the colors  with a filter of complementary color placed over the
camera lens. This principle applies also to the invisible areas of the spectrum
but we need films which can "see" in these areas in order for our own eyes to
see the differences if they exist.

Since UV and IR wavelengths are invisible to our eyes and thus can not be
assigned a "color" as such, B&W film is the most appropriate to use for both of
the above applications. Almost any B&W film can be used for  reflected UV
photography although the slower emulsions seem to deliver somewhat better
negatives. To record the IR wavelengths Kodak High Speed Infrared film should
be used. It is also about the only IR emulsion readily available! Since the
film has no antihalation backing allowing light and IR to pipe into the
cassette it should be loaded into the camera in total darkness or under subdued
fluorescent illumination. Fluorescent tubes usually are very weak in IR output
diminishing the chance for fogging the film by IR rays passing into the

When attempting either UV or IR photography the subject must be lit with lights
which emit the wavelengths by which we wish to photograph.Electronic flash is a
good source of both UV and IR wavelengths. Some flashes have a UV absorbing
filter incorporated in the flash head and this may need to be  removed (if
possible) for best results. However, even if not removed, there is usually
enough UV that "leaks" through so that at close range they still serve as
useful UV sources. Then,  placing a UV transmitting filter (Wratten 18A) or IR
transmitting filter (Wratten 87 or 87C)over the camera lens will effectively
expose the film only to the wavelenghths of interest.

Under certain conditions it is possible to previsualize the approximate
appearance of a UV scene by installing into the camera a groundglass covered 
with a fluorescing substance. The UV energy passing through the lens causes
this substance to fluoresce and the UV scene becomes visible in the finder!

In order to continue to use a 35mm SLR camera for reflected IR photography even
when you use the visually opaque 87 filter for photography it is possible to
install the filter behind the camera's mirror mechanism and composition of the
IR picture becomes almost as easy as if you were using "light" for your
pictures. In some cameras with behind the mirror metering  systems the filter
may need to be positioned just in front of the film between the film plane
guide rails. Metering off the film may be impossible.

While exposure is most appropriately determined in either case by making a set
of test exposures or by bracketing it may be possible to establish a UV or IR
"personalized speed index" by using one of the new ultrasensitive light meters
but metering through the UV or the IR filter and correlating the exposures that
seem to deliver negatives which you judge acceptable by your own standards with
those suggested by the meter. You should generally only attempt to establish
this personalized speed index metering in the reflected mode. Finally this does
not preclude bracketing but you may more consistently arrive at the proper
exposure with less waste.

The focal length of a given lens "changes" with wavelength and for this reason
its focus should be adjusted slightly when attempting to use it for other than
light wavelengths. The lens must be moved somewhat further from the film than
visual focus demands when photographing by IR and generally also when
photographing by UV. The reason for this is that most camera lenses are
achromatic in color correction (unless otherwise stated to be simple, very
unlikely, or apochromatic in correction) and thus curve the chromatic focal
plane about two visible (except in some cases with lenses intended specifically
for UV photography) wavelengths thus bringing both IR and UV to a focus further
from the film plane than visible wavelengths. Under normal conditions the use
of small apertures will in most cases diminish or eliminate the need to make
this focus adjustment. When using a fluorescing screen in UV photography the UV
rays are properly focused when the image on the screen is sharp.

I've already mentioned the term "fluorescence", and most of us are aware of the
term but may not be quite sure of what process is at work. When some subjects
are illuminated by certain wavelengths they reflect back not only the same
wavelenghts that they are illuminated by but they may transform some of these
incident wavelengths into usually longer ones. In a sense they change the color
of the light falling on them. When a subject behaves like this it is said to
FLUORESCE. Some subjects change short, ultraviolet energy into longer, visible,
wavelengths or colors. Others may change visible rays into yet longer, infrared
wavelengths. The former effect is, of course, visible while the latter is not.

This is the realm of FLUORESCENCE photography and to apply it you need to start
with a source that contains the wavelengths which the subject will transform
into longer wavelenghts. Usually over this source is placed an EXCITER filter
the function of which is to allow only those wavelenghts  through which will
cause fluorescence. In UV work this is most commonly the Wratten 18A filter and
in the visible region of the spectrum the Corning filter #9788 can be used. To
photograph fluorescence excited by UV, which usually results in a visible
effect, color film can be used to good advantage with Kodachrome 64 being
paricularly suitable. Since not only the "new", visible, wavelenghts are
reflected from the subject but also some of the UV transmitted by the exciter
filter, a UV blocking filter, called a UV barrier filter, is placed over the
camera lens to allow the film to record only the fluorescence. For UV work this
barrier filter is the 2E or similar, pale yellow, filter. Exposure may possibly
be metered in the camera especially with the newer more sensitive in-camera
meters. No focus compensation is necessary.

To photograph IR fluorescence (or as H.Lou Gibson calls it: IR luminescence)
the B&W infrared film should be used. The exciter filter placed over the light
source must not allow any infrared rays through to the subject. The Corning
9788 is just such a filter and it can be obtained from the Corning Corporation.
It is a glass filter and since it will be used over the light source it can be
of low optical quality. Even so, it is almost as expensive as the 18A filter
(which should be of optical quality) although for a much larger size. Six
inches square vs. three inches square for the 18A, at a price of about $100 for
the 9788 and $150 for the 18A. The barrier filter should be a deep red or
infrared filter such as the 87 or 87C. Camera focus should be adjusted as per
previous discussion. Metering is not possible because the effect ocurrs in the
IR and most meters are designed to meter light, not infrared. Even meters with
IR metering capability would probably fail to detect the presence of IR
fluorescence because of the very low amounts of IR produced in this fashion.

The four techniques briefly summarized above have widespread application in
document investigations and forensic photography, in surveilance and in
environmental studies. Also in medicine, mineralogy, philately, art
history,etc. Generally one sets out on a voyage of discovery when faced with a
new subject. One tries each method in turn, hoping that one of them will yield
better information about the subject than that which the unaided eye can
perceive. Each new subject becomes a most exciting photographic adventure. 


The sample is illuminated by "white" light and an 18A filter is placed over the
camera lens, tightly fitted. If the subject does not fluoresce then you can 
place the filter over the light but you need to work in a dark room.

This technique is useful for the photographic enhancement of rashes and other
skin disorders and also for detecting alterations in documents, etc.

Suggested light source: Electronic Flash (best if flash does not have UV
                        absorbing coating)
Filter on camera      : 18A
Appropriate Film      : Most any B&W film, especially slower emulsions
Lens                  : Should be able to transmit UV. Most camera
                        lenses are suitable for long wave UV associated
                        with use of 18A filter over lens.

Under special conditions, such as when a short wave UV source is available,
photography is done in the dark and the 18A filter is not used. Subjects that
fluoresce will be recorded as a mixture between reflected UV and visible
fluorescence. When photographing with short wave UV (around 254nm or less)
energy, typically provided by special sources, many standard camera lenses are
unsuitable because the glasses they are made of absorb such wavelengths. Quartz
or mirror lenses may need to be used although pinholes and some plastic lenses
are an alternative. Under very short wave UV conditions the gelatin of the
emulsion itself may absorb the incident rediation. In this case special
emulsions with silver halides deposited on the surface are used. 

Exposure  : Generally determined by trial.
Focus     : Camera focus must be adjusted for critical use.


In its most common practice the sample must be irradiated with UV rays and due
to fluorescence it will "GLOW" in the visible region of the spectrum. The
sample will appear in various colors as a result of the effect the sample has
on the incident energy. Because samples also reflect some UV as well as
fluorescing, the unwanted UV is removed with a "barrier" filter opaque to UV.
The filter which limits the incident energy to  a desired spectral region is
known as the "exciter" filter. This technique is particularly useful for the
identification of minerals and  for "fingerprinting" documents such as stamps
and currency. It is also used in forensic work with fluorescing powders in
fingerprint visualization.

Light source suggested  : Electronic Flash or UV emitting lamps
                          operating in a darkened environment.
Exciter filter suggested: with lamps it's built in so none needed
                          with electronic flash use 18A over flash.
Barrier filter suggested: Wratten 2A or 2E
Appropriate film        : Color reversal daylight film seems best.
                          Effect is in color so B&W film less useful.
Exposure  : Can often be determined with built in meter but light level 
            is much lower than it might appear visually.
Focus     : Visual focusing on groundglass possible.


The sample can be illuminated by "white" light and an 87 or 87C 9or similar)
filter is placed over the camera lens, tightly fitted. In a darkened room the
filter may be placed over the light source. Sometimes a filter is not required.
For example, a flatiron may be used as a source of IR radiation and if
operating in a dark room no filters are needed. 

Some photographers use a #25 filter over the lens of SLR cameras in particular
so that they can focus on the image in the groundglass. Alternatively, the
visually opaque IR filter may be inserted behind the camera's mirror.

This technique is useful for the recording of subcutaneous (below skin) veins,
for the detection of alterations or forgeries of documents, for

Light source suggested  : Electronic Flash, floodlights or daylight.
Filters suggested       : 87 or 87C over camera lens.
Film                    : Kodak High Speed Infrared
Exposure  : Determined by trial, use manufacturer suggested data, 
            or using CdS Luna Pro and metering through 87C filter 
            set ASA guide to a speed of 2400.
Focus     : For critical results it must be adjusted.


As in fluorescence excited by UV certain samples transform shorter wavelengths
into longer ones which in this case are in the invisible IR region. This
effect is sometimes called "luminescence" and the sample is usually irradiated
with BLUE-GREEN light without any IR present in the beam. A barrier filter
which allows only the newly created IR wavelengths to pass into the camera is
placed over the lens. Best to work in a dark, IR free, environment.

This technique is particularly useful for the study of inks, hardwoods and
forgery detection in forensic photography.

Light source suggested  : Tungsten or Electronic Flash.
Exciter filter suggested: Corning 9788 over light source plus Corning
                          3966 heat absorbing filter placed between
                          source and the 9788 if using tungsten source.
                          Certain blue-green lasers also may be used 
                          without any filters.
Barrier filter suggested: Wratten 87, 87C or 88A
Film                    : Kodak High Speed Infrared
Exposure  : Determined generally by trial. Expect it to
            be extremely great.
Focus     : Must be adjusted for critical results.

Note: when IR reflected light photography is done with COLOR INFRARED film,
then "white" light plus IR must fall on the sample, thus a Wratten #12 is used
over the camera lens to remove from the incident radiation the blue light to
which the three layers of the IR COLOR film are all sensitive.

Note 21.08                   -< Solarization Tip >-
    There was an interesting suggestion posted on the Internet that I thought 
    might be of help if you are trying your hand at solarization (Sabattier). 

    > My students just finished using dektol and Ilford Multigrade rc with
    > a #5 filter and a #5 filter in the white light source. They all seemed 
    > to get pretty good results.

    That would make sense...under those conditions, a Variable Contrast 
    emulsion becomes essentially a single-layer graded emulsion. (The second,
    green-sensitive, low-contrast layer is completely out of action.) I
    had tried the #5 filter in the image light, but not on the fogging
    light.  I'll try that...

    Richard Hosker 

Note 21.09         -< Create-a-Print used for B&W printing >- 
> Has anyone figured out a way to use  black and white  negatives other than
> xp2 in the create a print? It doesn't seem to want to accept non-bar coded
> negatives, and i was wondering if there was a way to override this...

    It's pretty easy.  Right above the negative eject symbol is a number,
    most often '1' but it depends on the last type of film inserted in the
    Create-A-Print.  Using the diamond key with the arrows (triangles) on
    it, move the cursor on top of that number and rotate the zoom control
    (one on the right) til the number gets to '40' .. turn it either right
    or left until it gets to '40'.  Then hit the button with the yellow
    circle on it and the machine is now set for B&W film.  You may need to
    turn that up or down while you are using the machine, using 41 or
    whatever (I think XP2 is 49) until you get the right color correction
    on the screen.  It will not be perfect at first, but make your own
    color corrections.  Good luck,

    Robert E. Klimkiewicz, Jr. -- Communication Major
    George Mason University  Fairfax, Virginia  U.S.A.
Note 21.10                  -< Decoding De DX Code >- 
                             DX codes decoded                                 

>1) Does any one have a clear view of the DX coding? What means what and how it
>is used. Especially interested in the meanings of each of the squares.

This info was transcribed from the June 1983 issue of "Modern Photography", 
page 8, by Markus Wandel  and he posted on rec.photo.   

	      =========================  <-- Light trap
	    +-| 1 | 2 | 3 | 4 | 5 | 6 |
Bottom -->  | +---+---+---+---+---+---+         <-- view of the film cartridge 
	    |_| 7 | 8 | 9 | 10| 11| 12|

The DX coding surface is divided up into 12 squares as shown.  Squares 1 and 7 
are ground, i.e. they are always bare metal.  The remaining squares are encoded
as follows ("*" means bare metal, otherwise square has nonconductive paint):

FILM                   FILM                EXPOSURE
SPEED  2 3 4 5 6       LENGTH  8 9 10      LATITUDE   11 12
----------------       --------------      ----------------
  25         *          12     *           +/- 1/2
  32           *        20       *         +/- 1      *
  40         * *        24     * *         +2/-1         *
  50   *     *          36         *       +3/-1      *  *
  64   *       *         -     *   *
  80   *     * *         -       * *
 100     *   *          72     * * *
 125     *     *
 160     *   * * 
 200   * *   *
 250   * *     *
 320   * *   * *
 400       * *
 500       *   *
 640       * * *
 800   *   * *
1000   *   *   *
1250   *   * * *
1600     * * *
2000     * *   *
2500     * * * *
3200   * * * *
4000   * * *   *
5000   * * * * *

Note 21.11     -< IR Ektachrome Processing in cool E6 chemicals >-
              How to process Ektachrome Infrared in E6 chemicals
    While it is true that E-4 chemicals should be used to process this
    film, it can be processed with E-6.  That is, if you can tolerate 
    somewhat weird colors.

    To process with E-6 first all temps must be at 75 degrees fahrenheit

    first developer				10
    -wash					2
    reversal bath				2	
    color developer				8
    conditioner	         			2
    bleach					10	
    fixer					10
    -wash					6
    stabilizer		        		2-3

    I have developed the two rolls that i was able to find like this.
    The results were fantastic, if only in an artistic sense.
    From: tom@po.CWRU.Edu (Thomas O. Moore)
    Organization: Case Western Reserve University, Cleveland, OH (USA)


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