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    FAQ or Answers to Frequently Asked Questions                  Section 22
    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 22 and its contents are listed below.

      22.01  -< Sunrise/Sunset location finder BASIC program >-
      22.02  -< Simple Sound Switch to trigger Flash >-
      22.03  -< Make Black Borders or Lines around your images >- 
      22.04  -< Sound Synchronizer for ECM application >- 
      22.05  -< Pinout Layout for Carousel Projector Receptacle >-
      22.06  -< Foot-candles - how to measure them? >- 
      22.07  -< Film Acceleration >-
      22.08  -< IR Film Data Sheet >-
      22.09  -< Circular Polarizers - better than square ones? >-

Note 22.01     -< Sunrise/Sunset location finder BASIC program >-
>Can someone point me to a source of tables or calculations for determining at
>what compass point the sun is going to rise on a given day at my latitude?

* please note that at the bottom of this contribution there is word of warning
  about the "simplicity" of this program esp. when used in exteme situations.

This is a little BASIC program that will do this.  It's quite simple, and makes
some assumptions that may be  slightly erroneous.  For example it assumes that
the earth is perfectly spherical and that the sun is an infinite distance away
from the earth, neither of which are true.  And it makes no allowance for uneven
terrain. However it should give results accurate to within a degree or so. 
Since even the best compasses generally available are calibrated in increments
of 5 degrees, it should be adequate for setting up photos in advance.

Note that the answer is given in TRUE degrees, which must be converted to
magnetic according to your local variation.  In North America, magnetic heading
= true - variation (around 20 deg.)

I thought it might also be useful to know the angle at which it rises and sets,
which can be quite steep.  For example, if you wanted to get a picture of the
sun rising over a steeple, at that height it may have moved quite a few degrees
North or South of the rise point.  So that's another thing to consider.  Please
verify the answers this thing gives before making plans for a complicated photo
I take no responsiblity for it's accuracy, useful- ness, or lack of same.  It
doesn't predict the time.  You can find that in the newspaper or the evening

If you want to know how it works, it's based on the fact that the sun is far
enough away that it appears to rise for everyone from the same direction.  In
other words, on one of the equinoxes the sun is directly over the equator. If
you were standing at the equator that day, it would appear to rise due East. 
But if you were in Alaska that day it also appears to rise due East, it just
doesn't get anywhere near as high (the rise angle is different).  On the other
hand, on June 22 it rises 23.5 degrees North of due East.  Again, it doen't
matter whether the observer is at the equator, the arctic circle, or the
Southernmost part of Australia.  This makes things fairly simple.

The rise/set angle is easy to find, because it's the same as the maximum  angle
that the sun will be at noon.  Said another way, the angular height of the sun
at noon is the same as the angle it makes with the horizon near sunrise/set
looking due East or West.

The basic equation used to find the heading is:

	sun angle = sin (d) * 23.5

	Where 23.5 is the angle (in degrees) of the Ecliptic plane to the
	Earth's equator, and d is the degrees of movement of the Earth in
	it's yearly revolution around the sun.  Conveniently, this is almost
	exactly the same as the number of days (360 degrees ~= 365 days).
	Day zero is considered Mar. 22.  For better accuracy, days are con-
	verted to degrees by the factor 360/365.25.  Since most computers
	use angles in radians, degrees are converted to radians by div-
	iding by 57.3.  (if your computer uses degrees, delete the first
	part of line 40 and use the second half.  The resulting sun angle
	I round to the nearest degree.
This is the angle of the sun with respect to the equator, from a viewpoint
external to the Earth.  This number is subtracted from the nominal heading of
90 degrees (East) for the rise heading, and added to the heading of 270 deg-
rees (West) for the set heading.  The rise/set angle is simply the difference
between the sun angle and your latitude.  Before giving an answer, some sim-
ple checks are done to make sure there actually will be a sun rise/set that
day, in case you're close to one of the poles.  That's about it.  Corrections
are welcome.

10 print "Sunrise/set Bearing Predictor, D. Richards 2/13/92":print
20 input "Number of days after Mar. 22: ";day : deg=day*360/365.25
30 input "Latitude (N assumed -- South is minus): ";lat
40 sunangle=int(sin(deg/57.3)*23.5+.5) :'40 sunangle=int(sin(deg)*23.5+.5)
50 if lat-sunangle >= 90 then print "The sun will not rise here this day.":end
60 if lat > 90-sunangle then print "The sun will not set here this day.":end
70 print "true sunrise heading = ";90-sunangle
80 print "true sunset heading = ";270+sunangle
90 risangle=lat-sunangle
100 if risangle=0 then print "Sunrise/set angle will be vertical.":end
110 print "Sunrise/set angle will be ";abs(risangle);" degrees from vertical";
120 if risangle>0 then print " toward the South.": end
130 if risangle<0 then print " toward the North.": end


From: daver@felix.filenet.com (Dave Richards)
Organization: Action Capture  Costa Mesa, CA

From:   IN%"kbagschi@astro.uni-bonn.de"  1-SEP-1994 08:51:38.80

I stumbled across the sunrise/sunset contribution in the PhotoForum's
FAQ-file (FAQ-22.01). The programm is indeed nice and simple, but I'm sorry
to have to tell you that it's _too_ simple. The assumptions made (earth
spherical, sun at infinite distance) are fine --- the error they result in
(< 1 minute of arc) are negligible when compared to the (errors that are
_unavoidable_ when calculating the) effects of refraction.
The real bug is, that, while it is true that the sun rises in the same
direction for everybody during the equinoxes, this isn't true on all the
other days (and at the poles, since there you only have the direction "south"
[respectively "north"]) --- if it were, then the earth would look
like a cylinder, between the arctic and antarctic circles, with an
undefinable top [bottom] changing it's shape in the course of a year.
The problem with sunrise/sunset calculations is that they can't be done
without _spherical_ trigonometry. If I use this programm for the 23rd
of March at a latitude of 89 deg. north, I get 90 deg. as the heading 
at sunrise with a riseangle of 89 deg. --- a programm resident in our LAN
(which does all the calculations we need to point our telescopes and a
lot of other useless things) gives me 29 deg. as the heading and a riseangle
of 5 deg.(BTW sunrise is at 2:00 local solar time).
It's a pity that I've got plenty of things to do until sunday --- before
I'll vanish in the Auvergne (France, Massif Central) 'til the end of 
September --- or I'd take a look in our library. I believe there was a
relative short programm doing simple sunrise/sunset calculations in one of 
the three (four ?!?) last copies of  Sky & Telescope  magazine.
Klaus Bagschik                          phone:  +49-228-73-5658
Radioastronomischs Institut             fax:    +49-228-73-3672
der Universit"at Bonn                   e-mail: kbagschi@astro.uni-bonn.de
D-53121 Bonn 
(Fed. Rep. Germany)                     "Per aspera ad astra!"
Note 22.02         -< Simple Sound Switch to trigger Flash >-
                    +9v             This device  will trigger a  flash  upon  
     o---.           ^   + 10uf     sensing a sound. Input should be a small
         |           |  .-|(--.     speaker or large ceramic microphone. The
         |           |  |     |     386 amp is set to 200x gain. The 3011 is
     ^   |          6|  |1   8|     an optocoupled switch.   Could use 3010.
         |        .--*--*-----*-.              
     I   \10Kohm  |             |               .----------.6          
     N   /       3|             |5    10uf +   1|          *-----> to flash
     P   \<-------*   LM386     *---*---)|------*   3011   |             (by PC)
     U   /        |             |   |           |          *-----> to flash
     T   \        |             |   Z  10 ohm   |__*_______|4
         /        |__*___*___*__|   |             2|                
     v   |          2|  4|  7|     === .1 uf       |
         |           |   |   |      |              |
     o___|___________|___|___|______|______________|________> -9v

Note 22.03    -< Make Black Borders or Lines around your images >- 
> Does anyone have any good tricks for burning in black borders around a B&W 
> print? Do you need a special easel or process for doing this?

To make black borders to the edge of the paper make yourself an opaque mask the
size of the desired image area. Actually tranparent red masks work even better.
When you make the enlargement  make it a bit  bigger than the mask you've  cut.
After the paper is exposed to the image  place and fix the mask onto the  paper
in the correct position and  with no negative in the enlarger  use the enlarger
as a light source to burn in the edges.  When you do this  you would be working
without the easel.Or with it if you can afford a thin white border on the final
print. This white border would, of course, be covered by the mat.

If you want a thin, black line  to go around your image area the concept is the
same but  the mask this time  cut so it  is a  little smaller than  the easel's
opening, goes over the image area after your image was exposed. Then you remove
the  negative from the  enlarger and burn in the  line between the mask and the
easel edges. If the mask is a little larger than the print area then you make a
thin white line.  Combinations of  masks and  sizes let you get quite  creative 
with borders and/or lines.                                                 Andy

From: andpph@ritvax.isc.rit.edu
Organization: Rochester Institute of Technology

I use Speed-E-Zels mostly, and I cut red construction paper masks that I slip
in the easel over the paper. I have masks in both 8x10 and 11x14 size. I cut a
rectangle in an 8x10 size sheet of red paper, then I trim off about 3/16 inch
from each dimension of the "hole". (You want to make those borders as thin as
possible.) I compose with the large red mask in the easel, leaving just a
little more room than normal. Then I expose with the paper under the mask. I
then position the rectangular insert so that there is an even distance on all
four sides. I take the negative out of the carrier and expose the "border" for
about 5 seconds. This produces a thin black border around the print with a
large white border. With the combinations of mask and insert, you can have a
large black border, a large white border, or the previously described large
white with thin black border.
I have masks of several different aspect ratios: 5 x 10", 7 x 10, 7 x 9, 7 x 7.
This allows customizing the image to the frame.  For some of the aspect ratios,
I have two versions, one for a horizontal image, and the other for a vertical

From: fohl@cbnews.cb.att.com (mark.e.fohl)
Organization: AT&T
Note 22.04        -< Sound Synchronizer for ECM application >- 
Here is a schematic for a Sound Synchronizer designed for use with an ECM
(electret condenser microphone).

          +6v      +6v               
           ^        ^   + 10uf     
        _  |        |  .-|(--.                     *----> flash (hot)
       | | |        |  |     |                     | a
    |--| |-/       6|  |1   8|                    _|_
       |_|       .--*--*-----*-.                  \ /  TIC106D
        | 20Kohm |             |                 __V__        
        |       3|             |5    100uf +   g  /|     
+-2V -->*----||--*   LM386     *---*---)|--------/ | c          
     +  |  .01uf |             |   |               *----> flash (GND)
       |O ECM    |             |   Z 100 ohm       |
     -  | mic.   |__*___*___*__|   |               |                
        |          2|  4|   7     === .047uf       |
        |           |   |          |               |
        |___________|___|__________|_______________|________> 0 v
       --- GND

For the ECM to work, you'll need about +2v at the point shown in the
schematic, this can obtained by trimming the +6v down with the 20k lin. pot.
But this might vary with the type of ECM used. Observe polarity of the ECM.
This circuit is fairly sensitive, but I'm working on some improvements...

From: Jeroen Steenblik
Note 22.05    -< Pinout Layout for Carousel Projector Receptacle >-
>I was wondering if anyone knows the pinout for the dissolve/lamp control port 
>on Kodak carousel slide projectors?  I'm referring to the rectangular 
>connector with one rounded end; the one you typically connect to an external 
>dissolve unit  (NOT the remote control connector).

This is described in a couple of pamphlets that were published by Kodak:
Kodak Slide Projector Wiring and Operation, Cords, Plugs and Receptacles for
Kodak AV Equipment, Reducing or Controlling Ligth Output of Kodak Ektagraphic
Projectors. Kodak may still have these available through their Info Service 
reachable at 800-242-2424.

In the last pamphlet there is an indication that placement of a switch, switch
plus resistor (fixed or variable), or diode between the two sockets located
directly below the 5 pins devoted to the "remote" control will allow you to
control the light level. Proper consideration of power requirements must be
taken. This is explained in detail in the pamphlets. 

I transcribed the illustration for you:
                         /           \
Small Red (forward      /             \
and chassis ground)----/--> o     o <--\---- Small Black (focus)
                      |        o <------|--- Yellow (common -- not ground)
Small White (reverse)-|--> o       o <--|--- Brown (focus lock)
                      |                 |
                      |                 |
       Large Red -----|--> o       o <--|--- Blue (to lamp)
   (to power switch)  |                 |
                      |  .............  |
                      |  : O       O :  |
                      |  :...........:  |
                             /__ Not used with projectors having
                                 permanently attached power cords

Note 22.06          -< Foot-candles - how to measure them? >- 
>My mother in law grows orchids and for some reason needs to measure the amount
>of light falling on them in foot-candles.  All the light meters she has are 
>graduated in ASA or somesuch. How can she measure in foot-candles with them?

The illuminance at the surface of the earth due to the sun at zenith on a clear
day is about 10,000 footcandles. These same conditions are associated with the 
"sunny sixteen" exposure rule of 1/ASA seconds at f/16. You can use this as the 
basis to compute other values of illuminance.

For example:

Set a light meter for ASA 10,000 and take an incident reading (or a  reflected
reading of an 18 percent gray card) of the garden illumination. The value in
footcandles will be approximately equal to the inverse of the exposure time in
seconds; e.g. 1/60 second is 60 footcandles, and 4 seconds is 1/4 footcandle.

From: Chris.Ellinger@med.umich.edu (Chris Ellinger)
Organization: Kresge Hearing Research Institute

Note 22.07                   -< Film Acceleration >-
From: slq2w@cc.usu.edu
Subject: Color Acceleration
Organization: Utah State University         

This is a copy of an article that I read in Photographic/November 1992.
by Marc S. Bloom
	ASSIGNMENT: Film acceleration is a Color III assignment at Brooks
Institute of Photography.  The process drastically increases film speed, but it
also radically changes the characteristics of the film; most notably, color
balance and grain.
	CHOOSING THE FILM: Select an E-6 transparency film and expose it at a
higher EI (exposure index).  Keep in mind that selecting a medium-speed film
over a high-speed one will result in less grain.  In choosing the EI, I
recommend a two-stop increase; for instance, from ISO 100 to EI 400.  This
procedure can be done with color negative film, as well, but transparency film
will enhance the grain effect.
	PROCESSING THE FILM: Follow these simple steps in order, for both
color-slide and color-negative films.

Step 1:  presoak the film in water (75 degrees farenhite) for two minutes. 
	 This will yield more even development.  Agitation will release air 
	 bubbles that may adhere to the film surface upon immersion. 
Step 2:  Develop in either Acufine, T-Max, or Perfection XR-2 developer.  Refer
	 to the chart for times and tempatures.  Agitate normally, as you woul
	 in developing black-and-white film (per your normal procedure).
Step 3:  Rinse in water for one minute, with agitation.  This will replace the
	 acid stop bath.
Step 4:  Fix the film in non-hardening fixer for five minutes.  Color-film
	 fixer, Rapid fixer without the hardening agent, or a fixer made from
	 Sodium Thiosulfate crystals, will work well.
Step 5:  Wash the film for ten minutes, with intermittent agitation.  From this
	 point on, you may expose the film to room light.
Step 6:  Bleach for ten minutes.  I recomend using E-6, C-41, or E-4 bleach
	 solution.  Refer to chart for homemade version.
Step 7:  Wash your film for atleast ten minutes.  Do not use Photo Flo solution
	 or other wetting agents
Step 8a: Bring your film to any profesionale lab to have it processed normally
	 in C-41 chemistry.  (Don't have the lab push process your film.)  You
	 can bring the film to the lab in the processing tank, wet, or you can
	 dry the film for easier transport.
Step 8b: If you choose to dry the film, rinse your film in deionized water,
	 with two or three vigrous tank inversions, then squeegee dry.  If your
	 lab questions your strange looking film, tell them that it will not
	 harm their chemistry.  The film will look badly underexposd, but this
	 is normal.  If you have rinsed your film for atleast ten minutes, and
	 refrained from using Photo Flo in your final rinse, the C-41 chemistry 
	 will not become contaminated.
	SHOOTING: Shooting a faster film will heighten the grain effect.
	RESULT: As you can see from the image, you don't get the normal tonal
rendition that you would if normally processed the film.  After you havr
processed you film and sent it to the lab for C-41 processing, you will have an
unmasked color negative.  It is no longer a transparency.
	PRINTING: In the printing make sure that the lab knows to print for
skin tone.  That way, everytging else in the photograph will not have any true
color rendition.  The results are fascinating!

Ektachrome 100  400   Acufine    12min.  75deg.
Ektachrome 200  400   Acufine     9min.  75deg.
Ektachrome 200  800   Acufine    12min.  75deg.
Ektachrome 200  1600  Acufine    16min.  75deg.
Ektachrome 160  320   Acufine     9min.  75deg.
Ektachrome 400  800   Acufine     9min.  75deg.
Ektachrome 400  1600  Acufine    12min.  75deg.
Ektachrome 400  3200  Acufine    16min.  75deg.
Fujichrome 400  800   Acufine    10min.  75deg.
Fujichrome 400  1600  Acufine    13min.  75deg.
Fujichrome 400  3200  T-Max      14min.  75deg.
Ektachrome 400  3200  XR-2       12min.  86deg.

	Start with 750ml of water at 75deg..  With constant stirring, add the
following: Potassium Ferricyanide (30 grams), Potassium Bromide (10 grams), and
water to make 1 liter.


Note 22.08                   -< IR Film Data Sheet >-
                         Kodak High Speed Infared Film 2481
                                    (Estar Base)
          * A high-speed, infared-sensitive black-and-white film on
          dimensionally stable .004-inch (0.10nm) Estar Base.
          * Sensitive through the visible region of the spectrum and in the
          infared to approximately 90nm, with maximum sensitivity from 750nm
          to 840nm.
          * Used in scientific, medical, biological, industrial and
          questioned-document photography.
          HANDLING: Handle only in total darkness. No safelight should be
          FILTERS: For most applications, a filter must be used over the lens
          (or light source) to absorb the blue light to which the film is
          sensitive. For general photography, a KODAK WRATTEN Filter No. 25
          is recommended for this purpose. If only infared is to be recorded,
          use a KODAK WRATTEN Filter No. 87, 87C, 88A or 89B or its
          equivalent. Under very low light conditions and when infared
          rendition is not important, the film can be exposed without a
          FILM SPEED: Exact speed recommendations are not possible because
          the ratio of infared to visible radiation is variable and because
          photoelectric meters are calibrated only for visible radiation. Use
          a hand-held meter rather than a through-the-lens type.
          It is recommended that trial exposures be made to determine proper
          exposure for the conditions under which photographs will be made.
          Under average conditions, the following speeds can be used as a
          basis for determining exposures when meters marked for ASA speeds
          or exposure indexes are used.
          No. 25, 29, 70, or 89B              50             125
          No. 87 or 88A                       25              64
          No. 87C                             10              25
          Without a Filter                    80             200
          FOCUSING: For best definition, take all infared pictures at the
          smallest lens opening that conditions permit. If large apertures
          must be used and the lens has no auxiliary focusing mark, establish
          a focusing correction by photographic focusing tests. A basis for
          trial is the extension of the lens by 1/4 of 1 percent of the focal
          length of the lens.
          DAYLIGHT EXPOSURES: -for subjects in bright or hazy sunlight
          (distinct shadows):
          Distant Scenes       Nearby Scenes               Distant Scenes
          1/125 sec at f/11    1/30 sec at f/11          1/125 sec at f/16
          PHOTOLAMP EXPOSURE TABLE: For use with a KODAK WRATTEN Filter No.
          25 over the camera lens. Use two 500-watt reflector-type photolamps
          or two No. 2 photolamps in 12-inch reflectors giving comparable
          light output. Place one lamp on each side of the camera at an angle
          of 45 degrees to the camera-subject axis.
          Lamp-to-Subject Diatance          3 feet       4 1/2 ft   6 1/2 ft
          Lens Opening at 1/30 Sec.         f/11           f/8        f/5.6

          FLASH EXPOSURE: To obtain the lens opening for electronic flash or
          flashbulbs, divide the guide number by the distance in feet from
          flash to subject.
          87 over the camera lens:
          Output of Unit     350 500 700 1000 1400 2000 2800 4000 5600 8000
          (BCPS or ECPS)
          Guide Number for    20  24  30   35   40   50   60   70   85  100 
          Distances in Feet
          Guide Number for     6   7   9   11   12   15   18   24   26   30
          Distances in Meters
          1. Develop:
          Approximate Developing Time (in minutes)
          Kodak Dev    Aprox     SMALL TANK-(agit at    LARGE TANK*-(agit at 
                     Contrast    30-sec intervals)      1-min intervals)
                                 65F 68F 70F 72F 75F    65F 68F 70F 72F 75F
                               18.5C 20C 21C 22C 24C  18.5C 20C 21C 22C 24C
          D-76         0.70      13  11  10  9.5  8     14  12  11  10   9
          HC-110       0.80       7   6   6  5.5  5      7  6.5  6  5.5  5
          (Dilution B)
          D-19 (max-   1.65       7   6  5.5   5  4     8.5  7.5 6.5  6   5 
          imun con-
          *Development times of less than 5 minutes in a large tank may
          produce poor uniformity and should be avoided.
          2. Rinse:
             At 65 to 75 F (18.5 to 24 C) with agitation.
          Kodak Indicator Stop Bath - 30 seconds.
          Kodak Stop Bath SB-5     -  30 seconds.
          A running-water rinse can be used if an acid rinse bath is not
          3. Fix:
             At 65 to 75 F (18.5 to 24 C). Agitate films frequently during
              Kodak Rapid Fixer      -2 to  4 minutes    
          OR  Kodak Fixer            -5 to 10 minutes
          OR  Kodak Fixing Bath F-5  -5 to 10 minutes
          4. Wash:
             For 20 to 30 minutes in running water at 65 to 75 F (18.5 to 24
          C). To minimize drying marks, treat in Kodak Photo-Flo Solution
          after washing, or wipe surfaces carefully with a Kodak Photo
          Chamois or a soft wet viscose sponge. To save time and conserve
          water, use Kodak Hypo Clearing Agent.
          5. Dry:
             in a dust free place.

          Keep unexposed film in a refrigerator or freezer at 55 F (13C) or
          lower in the original sealed container. If the film is stored in a
          refrigerator, remove it four hours before opening the package. If
          stored in a freezer, remove it about eight hours before opening. A
          sufficient warm-up time before opeing the package is necessary to
          prevent condensation of atmospheric moisture on the film.
          Keep exposed film at 40 F (4 C). Process the film as soon as
          possible after exposure to avoid undesirable changes of the latent
          image. If it is necessary to hold exposed but unprocessed film for
          several days, it should be resealed and refrigerated. Before
          unsealing and processing exposed film that has been stored in a
          refrigerator or freezer, follow the moisture prevention and
          handling procedures for raw film as described above.
          FOR MORE INFORMATION: see the following Kodak Publications
          No. M-28, Applied Infared Photography
          No. N-1,  Medical Infared Photography
          No. N-17, Kodak Infared Films
          This film will be replaced if defective in manufacture, labeling or
          packaging. Except for such replacement, the sale or any subsequent
          handling of this film is without warranty or liability even though
          defect, damage or loss is caused by negligence or other fault.
          Eastman Kodak Co, Rochester, NY  14650
          Kodak, Estar, Wratten, D-76, HC-110, D-19 and Photo-Flo are

Note 22.09    -< Circular Polarizers - better than square ones? >-
From: bbowen@megatest.com (Bruce Bowen)
Subject: Circular polarization, what and why.
Organization: Megatest Corporation
> I understand how a polarizer works, can somebody explain to me how a circular
> polarizer works please?  Should I have spent the extra money for this? 



    Circular polarization is a form of polarization for light (and other
    transverse 2-D waves) where both horizontal and vertical components are
    present, but they are coherent with each other and 90 degrees out of
    phase.  So instead of going "up and down", or "right and left" as in
    linear polarization, you get a field vector that rotates in a circle,
    either CW or CCW, and never goes through zero.

    For example, if you take a clothesline, tied at one end, and wiggle it
    up and down, you get a linearly polarized standing wave, if you rotate
    it around in a circle like a jump rope you have a circularly polarized
    standing wave.


    Modern autofocus cameras employ dielectric beam splitters in their
    autofocus mechanisms.  These are sensitive to, and don't work properly
    with, linearly polarized light (for those of you who are familiar with
    optical refraction and reflection, think "Brewster angle").

    In order to get the advantages of a linear polarizing filter with a
    modern autofocus camera, you use a linear polarizing filter with a
    second coating on the back that de-"linear polarizes" the light after
    the other linear component has been filtered out.  This second layer
    turns the linear polarized light reaching it to circular polarized
    light, which is compatible with the beam splitters.

    Fun things to try:

    I've never done this, but it should work.  Take two circular polarizing
    filters.  Have their fronts facing inward toward each other.  As you
    rotate one with respect to the other you will see the normal linear
    polarizing effect of it going light and dark every 90 degrees (so, what
    else is new). Now take the far filter and turn it arround so that the
    front of the near filter is facing the back of the far filter.  Now as
    you rotate around,  nothing will happen (or it may still go through
    the light and dark cycles, but not as intensly.)

    -Bruce		bbowen@megatest.com

                            PhotoForum (Internet)
by the way ... if you want to subscribe to the PhotoForum list for photo and
imaging educators, students and others interested in the topics that might be
discussed by such a group you can do so by sending mail to: 
with this text in the BODY of the mail: 
subscribe photoforum your-name-here
where it says your-name-here substitute your real name and then send message.
Also, there are a number of articles available from this server. Get to them
at the following URL: http://www.rit.edu/~andpph/articles.html

For info on a global databank of schools offering photography instruction go 
to: http://www.rit.edu/~andpph/database.html

FTP: You can also obtain most of these files also by Anonymous FTP from 
   vmsftp.rit.edu under pub/ritphoto/photoforum

WWW: You can access the PhotoForum Home Page on the WWW at the this address: