[PhotoForum logo]

The PhotoForum on the Internet is an email based photo-imaging
education and professional practice discussion list

    FAQ or Answers to Frequently Asked Questions                  Section 34
          Please check "root" (faq$txt) file for acknowledgements. 
    This is a file containing answers, tips, hints and guidelines associated 
    with recurring  questions asked by photographers.   If you would like to 
    add a tidbit of knowledge to  this list just send it to   ANDPPH@rit.edu 
    who will gladly add it to this collection. For complete table of content
    send message to   ritphoto@rit.edu   with  FAQ$txt  in the Subject: line
                    These files are available in SECTIONS. 
             This is Section 34 and its contents are listed below.

    34.01   -< Accounting for extension tubes and exposure factors >-
    34.02   -< Developing Tech Pan film recommendations >-
    34.03   -< Managing Polaroid Type 55 Pos/Neg film in the field >-
    34.04   -< Pinhole Resources and the Hole Thing >-
    34.05   -< Multiple Exposure Capability - what good is it? >-  
    34.06   -< How are higher flash sync speeds achieved >-
    34.07   -< Front projection for professional backgrounds >-
    34.08   -< Desensitizing film for development by inspection >-
    34.09   -< How much light does it take to expose film properly? >-
    34.10   -< What is a diopter? >-
    34.11   -< Daylight balanced fluorescent tubes and correction filters >-
    34.12   -< How are the faster X sync speeds achieved these days? >-
    34.13   -< How to adjust the tension on a Graflex Focal Plane shutter >-
    34.14   -< How does a teleconverter change Depth of Field? >-
    34.15   -< Title slides with BLUE backgrounds - how to make them? >-

Note 34.01   -< Accounting for extension tubes and exposure factors >-
>I just bought a set of extension tubes for my medium format camera. The short
>tube requires an exposure adjustment of 2X, the longer one 3X. In terms of
>exposure stops ie: full f-stops OR shutter speeds, can someone explain to me 
>how to adjust the exposure for each tube and when the tubes are used together.
If you are using a plain extension tube (absolutely no lens elements in it) the
amount of exposure adjustment is dependent upon BOTH the length of the
extension tube AND the focal length of the lens being used with it!!! In other
words, using a 25mm extension tube with a 50mm lens is a different exposure
adjustment than using the same 25mm tube with a 200mm lens.
   You can use this table for your calculation of exposure adjustment. 
     Extension / focal length               Exposure increase in EV
                                                  or f/stops
      1/10 - 1/5                                     1/2
      1/4 - 1/3                                      1
      1/2                                            1.5
      1                                              2
      1.5                                            2.5
      2                                              3  
If you're into the real math, you can calculate the Exposure Factor (not the
same thing as exposure increase in the above table... Exposure Factor 4 =
exposure increase of 2 f/stops, for example).
       EF = (Magnifaction+1)^2
  where Magnfication = Extension / Focal Length. We can convert both into a
  single equation for simplicity:
       EF = ((Extension / Focal Length)+1)^2
   Got that? 
From: WiltW@aol.com
One of the easiest and most versatile ways to make exposure compensations for
longer than normal lens-to-film distances, or "bellows extension", as it is
often called, is to use a variation of the inverse square law.
To do this, you will have to measure a standard distance from a point on the
lens to the back of the camera. This "standard distance" MUST be equal to the
focal length of the lens you will be using with the tubes. For example, you
mentioned MF, so I'll assume an 80 mm lens. Measure from the back of the
camera to a distance of 80 mm, and note that point on the lens. This is your
normal lens to film distance, or "old extension, as they sometimes say. Now
put on the longest tube you have, and measure that distance again. Let's say
it's 140 mm now. Note: the longest tube will give you the difference between
the two numbers. You actually use whatever will do the job.
The formula is: the new lens extension squared divided by the old lens
extension squared, or 140 squared divided by 80 squared, or 19600 divided by
6400, or 3.06. "3" is certainly close enough. That translates to a one and
one half increase in exposure. So if the meter says shoot at f/11, it's one
stop, or twice the exposure, to f/8, and if you want twice more, or four times
altogether, it would be f/5.6. You want a point in between 5.6 and 8 to equal
a three times increase.
This will become second nature in no time. The nice thing about it is that it
works for 35mm cameras and normal lenses, or wide angle or telephoto lenses, or
4 by 5 cameras with the bellows racked out 3 miles, or what ever else you may
be working with. You can make extension tubes of old paper towel tubes, and it
will work flawlessly. It works for my Robertson Meteorite copy camera, which
takes up to a 15 by 18 inch negative. And it works exactly the same for every
conceivable situation.
Summary: take the new focal length of the lens, or the new extension, square
it, (or multiply it by itself if your calculator doesn't have an x squared
key), and divide that by the old focal length, or *actual* focal length,
squared. That is your exposure factor. Increase exposure that much, and you
can't miss. Works every time, unless you really go overboard and start getting
into reciprocity failure.
Math, yes, but if you want to do some serious closeup work without in camera
meters, it's a necessity, especially for slides.
John Thompson, Canton, Ohio
From: "John D. Thompson" 
There are probably many ways to arrive at the answer you are looking for. I
would approach it from the point of view that a factor of 2 is one stop. I also
know that the log of 2 is .3   From here, if I need an exposure increase
associated with a factor of 2x I find the log of this factor and divide it by
.3 to find the increase in terms of stops.
For example: need an increase of 2x. The log of this factor is .3
                                      divided by .3 the answer is 1 stop
               "   "    "        3x  The log of this factor is .47
                                      divided by .3 the answer is 1.6 stops
now I if I place both tubes on the camera and use the two "factors" together, 
their "power" is multiplied. This is because if I need a factor of two and add 
a stop, and then I need (for some reason) another factor of 2 on top of that 
I'd open up another stop. The total would be two stops or a factor of 4. Thus 
factors get multipled. In the case you mention, 2 x 3 = 6 and thus to continue:
For example: need an increase of 4x. The log of this factor is .6
                                      divided by .3 the answer is 2 stops
               "   "     "       6x  The log of this factor is .78
                                      divided by .3 the answer is 2.6 stops
andy, andpph@rit.edu
Note 34.02      -< Developing Tech Pan film recommendations >-
>Does anyone have any suggestions for developers with Kodak Technical Pan? I'm 
>a scientist and use it in microscopy because of the low grain.  I also use it
>at home for wildlife and macro work. I currently use Rodinal which brings ASA
>up to around 50.  Any suggestions?
I have had considerable success with modified POTA developer. Formula follows:
water (125 F)            750ml
Sodium Sulfite (anhyd)   25 gm
Kodalk                  1.0 gm to 1.5 gm  
Phenidone               1.5 gm
Benzotriazole 1% sol.    15 ml
Water to                1.0 l
The activity of the developer changes wit its oxidation state and it should be
used immediately. This is inconvenient for two reasons; first, the warm water;
second, Phenidone is very hard to dissolve. So I make a 5% solution of
Phenidone in denatured alchohol (or in 99% Isopropyl Alchohol if you can get
it) and a 2% or 5% solution of Benzotriazole in denatured alchohol.  Both of
these chemicals are readily soluble in alchohol.
Using these premixed solutions, I can then mix the developer at normal
processing temperature and immediately use it. Processing time is about 15
minutes at 20 C (68 F), with 30 seconds initial agitation and 2 seconds shake
every 30 sec. (as advised for Technidol liquid). This produces a useable EI
of 25 or 32.
I have heard that a useable EI of 50 is possible if TechPan is developed in
Flexicolor (Kodak's C41) developer. I have not tried it.
In 1982, I produced an excellent metol-based divided developer that produced
beautifully graded negatives at EI 40. Processing consisted of diluting a stock
solution for the first solution, processing for three minutes with continuous
agitation, then replacing the first solution, without rinsing, with a
sulfite/carbonate solution for three minutes with continuous agitation. If
anyone's interested, I can dig it out and post it. (or send it to you)
Tech Pan is a bit fussy, but it is a truly beautiful pictorial film, especially
if you enlarge to billboard size.  The limiting factor with this film is your
optics and technique, and not the film. Best of luck!
    _/_/_/_/ _/_/    _/ _/   | Edward M. Lukacs 
   _/       _/ _/ _/_/ _/    | eml@gate.net 
  _/_/_/   _/  _/  _/ _/     | 11286 Southwest 169 Street 
 _/       _/      _/ _/      | Miami, Florida 33157 USA 
_/_/_/_/ _/      _/ _/_/_/_/ | Telephone: (95) 305-235-9098 
Try using TMax developer at various dilutions. My notes on this are at home so
I can't be too specific, but I suggest you try dilutions of 1:14 to 1:19,
development in the 6-10 minute range, and rate the film at 16-25. My impression
of my experiments with TMax was that there was good control of contrast, good
consistency over several rolls developed over a number of weeks, and
development was very even. I was able to use my normal agitation method rather
than lowering films into the tank as Kodak recommends for Technidol. 
There is a good article in the March/April 1992 issue of "Darkroom and Creative
Camera Techniques" on processing Tech Pan. Among other things it suggests using
Kodak Flexicolor developer, 10 minutes at 20 degrees C. Rate the film at 50.
There is also a formula for a stop bath for this procedure.  I've done it a few
times with satisfactory results, although you may want to rate the film at 20
rather than 50.
John Poirier, Coordinator of Technical Services, Northwest Territories Archives
Yellowknife, Northwest Territories, Canada John_Poirier@tailbone.learnnet.nt.ca
I have been using C-41 Flexicolor developer with Tech Pan for normal contrast
work for some time and have been quite happy. It seems less prone to producing
the development problems I experienced with other developers, especially with
120 film. It is certainly cheaper than Technidol and does not require any fancy
mixing. I originally read about it in an article in _Darkroom Techniques_, by
Hans Dietrich. He claimed an ISO of 50, but I get about 25-32.
My procedure:
1.   Pre-soak the film about 2 minutes in water, with intermittent agitation.
2.   Dump the water, turn out the lights, and remove the lid and film.
3.   Pour the developer into the tank.
4.   Drop the film into the tank of developer and replace the lid.
5.   Agitate by inversion for 30 seconds. Agitate 5 seconds every 30 seconds
     for the full time (9 minutes at 68 degrees F).
.....continue as usual..
As with conventional films, and at least as important, make sure there is a bit
of air space between the top of the solution and the lid. This ensures that
there is adequate turbulence during agitation.
I use No.2 paper and a cold light/diffusion enlarger head. I have read that
the grain of Tech Pan is so fine that it is not subject to the Callier effect,
so this development time may work for condenser enlargers, too. As you
probably know, Tech Pan is sensitive stuff, so your results will likely vary
from mine.
.  ****************************************************************
.  *    Nathan Prichard          *    Kentucky Historical Society *
.  *    Internet/e-mail:         *    Box H                       *
.  *    npric1@ukcc.uky.edu      *    Frankfort, KY   40602       *
.  *                             *    U.S.A                       *
.  ****************************************************************
From: Jim Thyer 
The developer given by Ed Lukacs is very similar to a developer I have used in
the past. It is  the "Delagi No 8 Developer" and I fount it in an article in (I
think)  Popular Photography, (the magazine name is not on my copy) but it was 
in the April 1981 issue. The only variations on the formula above are:
Use Kodalk OR Borax  0.8 gm.  (May be 1 gm. Kodalk gives slightly higher 
                               contrast, Borax yields good developer activity)
Phenidone  1.4 gm.  
Use at 68 deg F, 15 minutes, use a liquid level about twice the height of the
film reel or reels for best results. Suggests 32 to 64  ASA rating. Good film
for detail, been around a long time (since 1977 as SO-115) and suprisingly 
few photographers have heard of it. I really enjoy the clear base and the
fact it lies flat, as well as its minimum  grain.
Jim Thyer      jrt@mfs1.ballarat.edu.au
Physics, School of Info Technology & Math. Sciences
University of Ballarat
Ballarat  Vic  3353  Australia.
Ph 053 279 236  int 61 53 279 236
Note 34.03    -< Managing Polaroid Type 55 Pos/Neg film in the field >-
>My question to all you pros is: How do you handle Polaroid 55 P/N negatives
>if you are on a shoot outdoors away from sinks and trays and running water
>etc.  Anyone who has some ideas on the best way to preserve the negs under
>these conditions please give me the benefit of your experience.
According to the Polaroid publication "Instant Innovations: Creative Uses for
Polaroid Films"  Mark Hauser of Chicago developed this approach to preserve
Type 55 negs in the field  appropriately sized plastic food containers (e.g.
Tupperware) about 2" high:
1. fill container with cold water & sodium sulfite solution
2. place two thin sponges on the bottom & cover with cold water
3. place a 4"x 5" piece of plain white paper towel (no design, no embossing) on
   top of the sponges
4. stack negs emulsion side down with a paper towel between each one
5. add two more sponges to top of "sandwich" before sealing with container top
After returning to base, treat the negatives in fresh sodium sulfite solution
and continue processing as indicated by Polaroid
The publication itself should be readily available thru a phone call to
Polaroid's technical assistance people. The number I have is 1-800-225-1618. So
far I've found the people there very helpful (even got a couple of free packs
of 669 once as replacements for problems).
If you're really into carrying a lot of stuff around and making your shoot even
more difficult, you might consider as an alternative the clearing tank marketed
by Graphic Designs (Shutterbug advertiser) which is a one gallon plastic bucket
and lid along with a plastic sheet film holder that doesn't really adjust to
the Type 55 neg size. The idea is to cart along the sodium sulfite solution &
pop your negs into the holder immersed in the solution as you are shooting. Of
course, you'll need a way to clean the stuff off your hands and anything else
it hits since it dries to a nasty white dust.
Or, if your 545 holder isn't too cantakerous, you can re-insert the covering
after exposure and remove the entire sheet without processing. Then reload the
exposed sheets into the holder later for processing. This is a method suggested
by Adams.
With the pack film equivalent, I exposed outdoors for some winter scenery
shots, then left the tripod outdoors, brought the film inside before pulling &
kept the sheet under my arm to bring it up to temp during the processing time.
If you are going to process in the field, you should pay attention to the
temperature. Polaroid is good but demanding stuff. It's really sensitive to the
Roy C. Zartarian, royzart@connix.com
A plastic bucket with a lid that gives a water-tight seal is available from
Graphic Center, PO Box 818, Ventura, CA 93002 (phone 805-641-1625). The bucket
comes with a rack that holds about a dozen 4X5 negatives, and with a supply of
sodium sulfite. Graphic Center calls this bucket the PN-10 Clearing Tank. I got
mine in 1990: the price then was 26.95, plus 5.00 for S&H.
--david  "rayfield@tardis.svsu.edu"
Invest seventy-nine cents in a small Tupperware or Rubbermaid container large
enough to hold the 4x5 negatives.  You can use the sandwich sized ones or try
to find one that opens vertically.
Mix the sodium sulfide solution to clear the negatives.  Pour into the 
Tupperware container.  As you make pictures, inspect the positive.  Put the
keepers in the sodium sulfide solution. When you finish for the day, pull out
the negatives, they shouldn't stick together in the solution and it's
impossible to "overfix" the things and wash them.
-fred,  fcollins@gonix.com (Fred Collins)
... I've always prefered to cart around a container of water rather than the
sodium sulphite solution. I then clear in sodium sulphite when I get home a few
hours later. I think the Polaroid literature says you can leave the negs in
ordinary water for up to 72 hours before proper clearing. 
Philip Jackson, 
I have encountered many of these same problems as you gents are describing.
Shooting type 55 in the field can be quite tricky. I have found what works
best for me and am glad to share it with you. First I learned the visual
relationship of what a good negative means a good positive will look like. I
usually find that the positive is 3/4 to 1 full stop lighter than a properly
exposed negative. When shooting in the field, I shoot off one exposure as a
test and judge it mainly from the positive. I trash the negative. When
assured that my exposure is correct, I shoot my final and carefully remove it
from the holder WITHOUT ROLLING THE DEVELOPER!! If you press the release
button you can remove the film with out developing. I have been told by my
friendly polaroid rep that the latent image will not degrade in quality for
over 2 months at least. I have made exposures and not developed them until
returning to my studio over a month later. This saves me all the hassle of
protecting and clearing negs while on the move.
If anyone else has found anything better, please let me know.

Note 34.04     -< Pinhole Resources and the Hole Thing >- 

A good basic book on pinhole is Jim Shull's The Hole Thing , there are examples
of cardboard box cameras which you could duplicate in wood. There is also The 
Pinhole Journal Star Route 15, Box 1655, San Lorenzo, NM 88057 you may want to 
contact. I believe they also sell inexpensive, beautifully designed wooden
pinhole cameras sizes 4x5 and up.

From: clp 
Try The Pinhole Resource, Star Route 15, Box 1355, San Lorenzo, NM 88041
505-536-9942. They have a catolog and a magazine dealing with Pinhole
Photography. Quite an interesting Magazine. Good Luck
Shaun, Camera Graphics Photolab, Albq NM 87106 

Note 34.05   -< Multiple Exposure Capability - what good is it? >-  
> I just got a camera with multiple exposures capability. When do you
> need to use this function and how ? Do you need a special filter so that
> your second/third exposure does not superimpose on top of the first ?
Well, if you don't want additional exposures imposing on the previous exposure,
just don't use the multi-exp feature at all.
'Course there's other handy uses of ME such as running a few distance checks on
your TTL auto flash ranges in a church or auditorium. If you use ME you can do
a bunch of tests and only waste a single frame of film.
Another use is to compile a long exposure from several pieces, allowing the
shutter to close if people walk by, lights glare, etc. If you want to paint
with light by flash, you can let the shutter close between exposures to avoid
background or stray light building up while waiting for flash recycling.
Regards, David Rosen dr8192@cnsvax.albAny.edu
There are bunches and bunches of ways to use multiple exposures. One that I've
been doing a lot in the lab I work in (an astronomy lab, not a photo lab) is to
take pictures of equipment. I set the camera up on a tripod, meter, and stop
down by a stop or so. The first exposure I do with the equipment case on. The
second exposure is with the case off the equipment. This results in a ghostly
case showing both the outside of the equipment, as well as the inside. Very
nice for documenting something you've just spent the last two weeks slaving
over with a soldering iron. ;)
Another use I've had for multiple exposures in the lab is in tracing laser
paths. The first shot is metered on the room with the room lights on, and taken
as such. For the second shot I kill the room lights and open the shutter. I
then go around the room and "paint" out the laser beams with a white index
card. Part of what our lab does is to manufacture diffraction gratings, so
after a beam diffracts off of one of our gratings we wind up with hundreds of
beams. They make for some very pretty, as well as useful pictures.
Play around with your multiple exposure function. It's lots of fun, and an easy
way to finish off a roll.
From: tom@peggysue.as.utexas.edu (Tom Benedict)
Organization: McDonald Observatory, University of Texas
Indeed, there are such filters. They shut one half of the lens. You can get
very funny results, for example when you set the camera on a tripod and focus
it on a bench. First you take the one half of the picture with a person sitting
on the bench on this side. Then you turn the filter round and take the other
half (2nd exposure) with the same person now sitting on the other side of the
bench, in different clothes or so. (some irrelevant material deleted)
But you can also use ME without filter. For example, you can photograph a
painting in red light, then -slightly move the camera- in blue light and then
in green light. You must underexpose each shot here. The results are quite
From: Marc Werner 
Organization: RWTH Aachen

In Marc's posting above what he probably is actually refering to is not exactly
a filter but rather a mask. A filter which is opaque on one side. This prevents
the film from being exposed on 1/2 the frame especially if small apertures are

Actually such a mask is probably better referred to as a matte, and the device
when made into an accessory, a matte-box. In matte-box photography positive and
negative masks are used to block and expose various areas of a scene 
sequentially. A camera capable of multiple exposures is very necessary for
technical perfection of this technique. Sometimes even the slight vibration
introduced into the camera body as the shutter and mirror do their thing is
enough to slightly move the film between shots. In such cases a pin registered
camera may be called for.

Andrew Davidhazy, andpph@rit.edu

Note 34.06       -< How are higher flash sync speeds achieved >-
>Would someone explain to me how the newer cameras sync faster than the 
>customary 1/60 (horizontal) and 1/125 (vertical fp shutter.) please?  Do they
>slow down the flash pulse so that it cover the entire "swipe" of the fast fp 
>shutter, or a number of strobe pulses along the full swipe of the fp shutter 
>or what? 
None of the above, if you mean the faster X-synch speeds. The shutters blades
simply move a whole lot faster. This means the film gate is wholey open for
exposure at shutter speeds higher than previous designs allowed. 
Curtain shutters traveling across the long dimension had, in past decades,
X-synch speeds of 1/25, 1/40, 1/60, 1/75, and 1/90. The higher X-synch speeds
are on the newer, faster moving curtain shutters. The vertical running bladed
shutters have X-synch at 1/90, 1/100, 1/125, a 1/200, 1/250, and 1/300. The
trend is the same. The faster X-synch speeds tend to be the newer shutters. 
This is due to stronger, lighter and faster-moving blades having to clear only
the shorter dimension of the gate.
Regards, David Rosen  dr8192@albNYvms or dr8192@cnsvax.albAny.edu
Faster FP sync speed are accomplished two ways as far as I can determine. The
first is that modern shutter "curtains" travel significantly faster than the
older designs and this allows cameras to raise the standard X sync speed by a
factor of approximately two or possibly four.
No FP camera, however, can sync with all flashes up to their highest shutter
speeds because at these speeds the full frame is not exposed all at once but is
exposed sequentially through the moving shutter "slit" created by the curtains.
Cameras that DO allow sync up to the top speeds must be used with special
flashes that flatten out the output of the flash by going into a "stroboscopic"
mode flashing at a rate of maybe 10K to 20K flashes per second for the time it
takes the leading curtain to go across plus the exposure time chosen. This
system is used in such cameras as the Olympus OM-4T. I did some testing of 
this system when it first came out many years ago. 
Newer flashes MAY employ a different scheme. I believe you can retreive a text
file with how this test was performed from an "archive" of articles available
at a site here at RIT. To check out what is available send a message to:
ritphoto@rit.edu stating in the Subject: line _and_ message body: articles$txt
Andrew Davidhazy, andpph@rit.edu at RIT's High Speed Photography Lab

Note 34.07      -< Front projection for professional backgrounds >-
>I have seen photographs where people are shown posed in front of a background
>of mountains, hills or other picturesque scenes. How is this done?
Generally, if done photographically it is done using a system known as 
front-projection. A front projection system projects an image of a scene onto a
highly reflective screen along the same optical axis as the lens of the camera
by using a beam splitting mirror placed in front of the lens. The mirror is
aimed at the slide  of the scene placed in the projector located generally
ahead and below the camera's lens. Sort of like this:
                semi transparent mirror          \<-flash or     |
      .--|--------|--.           ------> /        \ ambient light|  
      |              |                 /           \       \ <-' |    high
      | from subject |____.          /              \  0    \    | reflectivity
      | __________________|________/_________________\000    \   |   screen  |
      |                   |      /--->------>------->--0      \  | <---------'
      | -<--------<-------+-<--/-|--->--<--->--<---->--<---->--<-|
      | from backgnd _____|  /   |                    00        \|
      |______________|     /     ^                   0 000      /|
                         /       |                      0      / |
         camera                  |                            /  |
                             .---+---.                       /   |
                             |   |   |                 ^         |
                             |   |   |                 |
                          .---   |   ---.              |
              projector   |      |      |       low reflectivity
                          |      |      |           subject
                          | =========== |
                          |    slide    |
The light from the projector is weak enough that most subjects do not reflect
enough light back to the camera to be visible. On the other hand the light that
falls on the screen is "retroreflected" back to the projector and the camera
lens also. The screen is a fairly specialized one I believe mostly made by 3M
and sometimes referred to as Scotchlite. It is not cheap! Standard projection 
screens are not reflective enough.
Hot lights or flashes lighting up the scene from angles other than the optical
axis do not affect the retroreflected light from the screen and mostly affect
only the lower and non directionally reflective surfaces of "standard" subjects
such as people, etc. 
Although there are several front projection system manufacturers I happened to
remember the one called the Scene Machine. Often this is the system used by
photographers making High School prom portraits and other similar events.
Customers choose the background they want and the photographer simply changes
the slide in the projector. Flashes are used for illumination in these set-ups 
and the projector is also typically fitted with an electronic flash that goes
off at the same time as the main units.
The photographers must make sure that the alignment between projector and
camera lens is properly set. There also is concern about the focal length of
the projector vs. the lens used in the camera.
Andy, andpph@rit.edu
Just to add another comment from 30 yrs of experience with these systems. Cost
is high for the screen material, from $1500 upwards for one mounted on fiber
glass which is probably all that has kept them from being in universal use. 
The systems were used for commercial work years before Henry Olds (Scene
Machine) made them popular for high school seniors and proms. The financial
advantage is in year around "seasonal assignments" in the air conditioned
comfort of a studio. The better systems use 2-1/4 slides so quality can be
quite high. While some claim to see a "line" around the subject, I'll assure
you that any such lines are the result of poor lens alignment at the beam
splitter or not enough distance from the projecting lens to the beam splitter.
The most effective use is not front projection alone but in "sets", for
example, a subject seated in front of a window (frame prop) using the screen
image in back of the set for the view ...or a subject touching a real tree
branch (cut and hanging on a light stand) with the projected image filling the
background. There can be far more to the creative work than selecting a slide. 
By taking advantage of the two different angles available (camera-slide and
camera-subject) you can take a subject coming out of a pool with water in the
background instead of the usual fence and chair clutter or, another example,
take a subject in front of a fireplace with the option of positioning the
"fire" instead of having it blocked as so often happens in the usual single
angle photography. Everyone has seen hundreds if not thousands of these images
but few recognize the angle distinctions. Because people can't see from two
completely different angles at the same time, this earlier version of "virtual
reality" is accepted without question!
Email if you are in need of specific info or a sample print for a project. 
J.M.Conway, timemark@aol.com

Note 34.08     -< Desensitizing film for development by inspection >-
> I was reading darkroom cookbook column in "Camera and darkroom" and saw that
> in one of the back issues there was an article on development by inspection. I
> thought this technique had been thrown out years ago!! Does anyone have any
> information regarding formulas for emulsion desensitisers and safelights etc.

I used to use Kodak Desensitizer. It's a purple dye. About a gram of powder
(that's all you used to get for over $20, and this was 20 years ago, or so)
makes a quart of reusable solution.
You soak the film in it, then you can inspect it under a green safelight
several times throughout development. I used to push high-speed recording to
over 16,000 ASA (I mean ISO). I would shoot rock concerts (they had low light
in those days) at 1/30 sec. (or faster if needed), then push the film 'til I
saw the proper image while inspecting. Sometimes I would resort to sticking it
in warm Dektol. Obviously, sometimes it would fog, but the "flash" actually
helped reduce the high contrast. Ah, the good old days.
David E. Le Vine
Safranin-O, a chemical closely related to, but more effective than
Phenosafranine, a well known desensitizer, is available at virtually any
chemical supply house. It is normally used as a biological stain, but is a
fine desensitizer. Any text on photochemistry, or the Photo Lab Index can
provide you with an appropriate formula and use instructions.
As an added feature, addition of phenosafranin to developers containing
hydroquinone as the sole developing agent results in causing the hydroquinone
to function as a soft-working developer. When Metol was very expensive, use of
a small amount of this dye with much cheaper hydroquinone produced the same
development action at much lower cost. 
Also, in my experience, Safranin-O is cheaper than Kodak's desensitizer.
From: Edward M. Lukacs, eml@gate.net

Note 34.09     -< How much light does it take to expose film properly? >-
>Do you know the formula for exposure?  It must be a function of shutter speed,
>aperature, exposure index and light levels. I guess light levels would be 
>measuredin footcandles or lumens. I know this isn't strictly linear.
First, Exposure is a function of Illuminance times Time. Illuminance being the
amount of light falling on the film (as opposed to Luminance which is how much
light leaves the subject). Exposure itself is linear. The photographic response
in terms of Density is not.
Going further, it is possible to determine the light level to necessary to
properly expose an average scene on a particular film. This is given by the
following relationship:
                                 25    times   F# squared
       Foot/Candles required = -----------------------------
                                 ISO   times   exposure time
The number 25 is a constant that "guarantees" that you will end up with
properly exposed negatives of average scenes. Sometimes slight departures from
this particular value are used depending on whether you like your negatives to
be thinner or denser than those given by using 25.
If you work this out to its logical conclusion you will find that the Sunny-16
rule assumes that there are about 6,400 foot-candles of illumination on a
standard scene for it to reproduce properly on average films at an aperture of
f:16 and an exposure time equal to the reciprocal of the ASA speed of the
andy, andpph@rit.edu
Note 34.10               -< What is a diopter? >-
> Can anybody explain to me what the diopter is?  Thanks.
A diopter is a a focal lenth measurement used by opticians for specifying eye
glasses. A diopter is the reciprocal of the focal length in meters. Some
close-up lenses are specified in diopters, e.g., a +2 closeup lens is a
positive lens with a focal length of 2 diopters or 1/2 meter.  The lenses that
are used to adjust a viewfinder to match your eyesight are called 'diopters'
because that's way they are measured.
Orrin - Long Island, NY | 70641.2173@compuserve.com
oedwards@hoflink.com    | orrin.edwards@hofbbs.hoflink.com

Note 34.11  -< Daylight balanced fluorescent tubes and correction filters >-
>Does anyone have information on the color balance of various fluorescent tubes
>which fit standard shop light fixtures available in hardware stores? Is there 
>a site on the net where this info is available. I'd like to use them as fill 
>occasionally for both still and video shoots.
I get mine from: Duro-Test Lighting, 9 Law Drive, Fairfield, NJ  07004
Their toll free customer service number is: 800-289-3876
I use the Optima 50 model for daylight balanced light boxes and 
overhead lights for viewing color prints, but I would guess they 
would be appropriate for shooting with also.
Dirk M. Schuneman, owner First Photo Lab, Orlando, FL, USA, Photo 1st@aol.com 
Flourescent tube manufacturers have tubes they consider to be daylight balanced
(ie:Chroma 50's) and tungsten balanced (ie: warm white deluxe) but from my
experience on film they aren't even close. Roscoe (movie supply company) makes
a magenta gel in large sheets that you can wrap cool white bulbs in that gets
them very close to daylight. Thats about the best match I've found (the light
looks very pink to the eye but neutral on film). They also have a gel you can
put over your strobes to convert them to cool white if you want to go that way
then filter on the camera.
Tom Collicott, Tomcoll@aol.com
Note 34.12   -< How are the faster X sync speeds achieved these days? >-
>Would someone explain to me how the newer cameras sync faster than the 
>customary 1/60 (horizontal) and 1/125 (vertical fp shutter.) please?  Do they
>slow down the flash pulse so that it cover the entire "swipe" of the fast fp 
>shutter, or a number of strobe pulses along the full swipe of the fp shutter 
>or what?  Thanks in advance ...  chuck
Faster FP sync speed are accomplished two was as far as I can determine. The
first is that modern shutter "curtains" travel significantly faster than the
older designs and this allows cameras to raise the standard X sync speed by a
factor of approximately two or possibly four.
No FP camera, however, can sync with all flashes up to their highest shutter
speeds because at these speeds the full frame is not exposed all at once but is
exposed sequentially through the moving shutter "slit" created by the curtains.
Cameras that DO allow sync up to the top speeds must be used with special
flashes that flatten out the output of the flash by going into a "stroboscopic"
mode flashing at a rate of maybe 10K to 20K flashes per second for the time it
takes the leading curtain to go across plus the exposure time chosen. This
system is used in such cameras as the Olympus OM-4T. I did some testing of 
this system when it first came out many years ago. 
Newer flashes MAY employ a different scheme. I believe you can retreive a text
file with how this test was performed from an "archive" of articles available
at a site here at RIT. To check out what is available send a message to:
ritphoto@rit.edu  stating in the Subject: line _and_ message body: articles$txt
andy, andpph@rit.edu
Note 34.13  -< How to adjust the tension on a Graflex Focal Plane shutter >-
              How to tension the Graflex Focal Plane shutter
This How To is for those who recognize that the rewards of learning how to "do
it yourself " must be weighed against the risk of potential failure. Don't
risk ruining your Super D if you aren't sure ! ;-D
By now the old and venerable spring in your RB auto Graflex or Series D has
lost its luster and doesn't pull the curtain fast enough. As a result, all
speeds are slow. Fortunately the fix is not too difficult for those with a
little patience and mechanical aptitude:
1. First make sure that the curtain is not rubbing anywhere and the curtain
selector is free to move (they often get bumped and then stick). It should
move very freely with no sticky spots.
2. Apply just a drop of lightweight oil into the two oil holes. These are the
little holes in the end of a round, flat, keyed metal piece on the left hand
side of the camera. Don't ever use or spray WD-40 or any spray lube or it'll
get in and mess up the works. Just use one of those little needle oilers like
the one sold in Radio Shack. Check to see if this improves things dramatically
- probably not ;-)
3. Look at the tensioning escutcheon (that's the plate that surrounds and
holds the tensioner) You'll see the tension knob, the release button and a hex
shaped cap. You should also see screws at the perimeter of the plate-don't
undo these yet. Release tension with the release button now. Then just take
off the hex cap (counterclockwise) to reveal the screw slot.
4. Find the right screwdriver to fit the screw slot before proceeding. Notice
that as you tension the shutter, the screw slot rotates. This slot is at the
end of the tensioning shaft and has to be tightened in order to increase the
spring tension. Don't try to force the screw since it's locked in place
relative to a gear under the plate.
5. Loosen, but don't remove, the screws holding the plate down. On the Series
D there are four screws. The idea here is to lift up the plate enough so that
the gear disengages from the shaft so that you can retension it. Put a thin
screwdriver in to hold the slot BEFORE you lift up the plate so that the
tension doesn't release suddenly. 
6. You may have to unscrew the perimeter screws a little more to disengage the
gear. Once accomplished, now is the time to guess how much more tension to
apply by turning the slot so that it gets tighter. I'm impatient so I give it
a good whirl thereby throwing caution to the wind. This can result in too much
tension which could overly stress the now ancient shutter curtain material, so
you probably should try moderate tensioning first. If the spring has lost its
temper, it will feel "dead" when you turn the screw - this is not the case and
the spring has some life left in it.
7. While still holding the tensioning slot push the plate back down to engage
the gear. Re-tighten the perimeter screws. Put the hex cap back on after
applying one drop of oil.
8. Test the shutter. I usually test with Polaroid having found the speed to
be reliable enough, however, if you have a flash meter you could make a setup
with a bright light to measure the relative shutter speeds. 
9. You may have to go back and do this again. Be patient, don't poke or pull
on the curtain in frustration, and don't curse me 'cause it's really easy and
self evident once you dive in. 
I love these old boxes and with care they ought to be useful tools for the
serious photographer. I am still learning the ins and outs so I don't claim to
be an expert by any means but I have found this procedure to be workable
several times now with no failures yet. 
PS - I've been asking around about how to convert some of these to Graflok
backs, a challenge that I have not attempted yet but will tell you about my
experiences and write a "how to" if there is any interest.
Bob Crowley, Staff Inventor, Input Devices, Wayland MA, n1ddzrjc@aol.com

Note 34.14     -< How does a teleconverter change Depth of Field? >-
>If you use a 2x converter with a primary lens at, say, f/22, will you get the 
>same DOF (Depth of Field) as the primary lens on its own at f/11?
No! Let's do the math.
1. Put simply, depth of field is a function of image magnification and f/stop.
2. Image magnification and lens focal length can be compared one to one. In
other words if you double the lens focal length the magnification will also
3. The change in DOF due to magnification is best described by the inverse
square law. a 2x factor change in magnification produces a 4x change in DOF.
Increase magnification and DOF will decrease.
4. F/stop values are relative to focal length. Increase the focal length
without altering the size of the aperature and the relative f/stop value will
change (increase/decrease?) (f/22 goes to f/45 with a 2x increase in focal
5. DOF changes due to f/stop do not conform to a fixed scale -- it's a log
scale. At smaller aperatures the change is greater. In other words the percent
increase in DOF produced by the change from f/22 to f/32 is greater than the
percent increase produced by the change from f/5.6 to f/8. To rough it out with
mid range aperatures considered, the change in DOF due to a full f/stop change
is between a factor of 1.3 to 1.6.
Now then. You've got a 100mm lens (35mm camera -- circle of confusion .00125
inches) set at f/22 and focused on a subject 5 feet away. The DOF is 13.8
inches. Switch to a 200mm lens at f/22 and do not move and the DOF decreases to
25% of the previous case -- 3.5 inches. (Obviously you're cropping the image
more tightly -- you have less information as magnification has doubled). Now
stop the 200mm lens down to f/45 (two stops) and the DOF increases to 7.7
inches or about half of what the 100mm lens produced at f/22 at the same
distance from the subject.
Let's do it with 2X converters: Take a 100mm lens at f/22 focused on a subject
5 feet away as a starting point (13.8 inches of DOF). Add a 2X converter and
the focal length increases to 200mm. The relative aperature is reduced (see #4
above) by two stops. If the f/stop setting on the lens (really a 100mm) reads
f/22 -- it is in effect f/45. If you do not move the camera position, DOF will
be 7.7 inches or roughly half of that produced by the 100mm lens at f/22 at the
same distance. If you compensate for exposure and set the 100mm lens to f/11
therefore achieving an effective relative aperature of f/22 for the now 200mm
lens the depth of field will drop to 3.5 inches or only 25% of that produced by
the 100mm lens at f/22.
Do the math.
Where N = near limit DOF, F = far limit DOF, H = hyperfocal distance, D = film
to subject distance, and L = focal length:  N = HD/H+(D-L) and F = HD/H-(D-L).
Joe Angert, <0007372155@mcimail.com>, St. Louis Communiy College
It seems to me that if you make a photograph at the same effective f# then the 
DOF in the photograph made with the teleconverter will be DOF of 50mm lens
divided by converter strength squared. Thus a 50mm lens operating at f:8 might 
have a DOF of 16 feet and when you insert a 2x converter making it a 100mm and
open up to f4 (effectively making it a f:8 100mm lens) then the lens will
exhibit a DOF of 16/4 or 4 feet.
If you stop the 50mm lens down to f:16 then since DOF is directly proportional 
to f# the DOF will be twice as large at f:16 as at f:8. If you switch to a 100
mm lens and use it at f:16 then DOF will be 1/4 that of a 50mm lens used at
f:16. Ultimately this means that if you use the 50mm lens at an effective
aperture of f:8 and the 50mm plus 2x converter at f:16, then the lens with the
2x converter will exhibit a DOF which is 1/2 that of the 50mm lens. If you
adjust the size of the image made by the 100mm lens to match the size of the
image made by the 50mm lens then the DOF of the two images will be the same.   
So, as long as you do not change the f# setting on your 50mm lens but insert a
2x converter behind it, the new DOF will be 1/converter strength of the old
DOF. If you enlarge the 50mm neg to match the image size produced with the 50 
+ 2x converter the DOF will be the same.                   
-anonymous -

Note 34.15    -< Title slides with BLUE backgrounds - how to make them? >-
>I want to do slides with blue background and text on white. Note: I don't 
>want to use a computer.
Here are 3 methods:
A       use slide film (100 ISO) to make a copy of your originals through a 
        yellow filter and then use C41 processing. All chrome films don't give
        same blue (FUJI was good) Try differents exposures.
B       lith film, lith developper (to generate a high contrast bw negative)
        use blue DIAZO film with UV light and process in vapors of amonia
        (diazo film can be found in most graphic arts shops)
C       Polaroid Polablue
- diazo need UV light and ammoniac process (problem with vapors) it is very 
  inexpensive and most applicable for BIG production.
- Polablue is very expensive (and need a processor)
- Slide film + C41 process is a good way for small production.
  Now I use computer !
Pascal MIELE, miele@ccr.jussieu.fr
The easiest way to do this, blue background and white letters, follows. Prepare
your text and graphs as black type on white paper, a laser printer works great.
Get a roll of slide film, the cheapest works great, and photograph the text and
graphs you need using a YELLOW filter (Y2 works great); you can even use
regular tungsten bulbs. Once you have finished, take the film to the lab and
instruct them to cross process it (develop it in C-41 chemistry). Usually cross
processing is cheaper than regular E-6, at least around here (Mexico City).
That is all there is to it.
Is there any need to state that you can get a green background and white
letters, red or magenta background and white letters, etc., etc., etc. Use your
imagination and your filters.
Francisco Garcia Maceda, carrillo@buzon.main.conacyt.mx
The process is reverse text slides. The best way is to use Kodak Vericolor film 
5072, SO-279 which is used to produce slides from color negatives. This film is
a clear base negative film C41 process.
Cat NO 122 1217  for the 30.5 meter bulk
cat No 162 2364  for rolls of 135-36
By printing out type on white paper from a word processor by laser or ink jet
printers you have to copy this on the above film with yellow filters. Simply
the black type goes white and the white background made blue. By using tungsten
lamps 3200k and a filter kodak wratten gelatin filters number 15 and 106 (amber)
and exposure at 6 ASA off a 18% grey card (my exposure is f8 for 2 sec this is 
a slow tungsten film and must be exposed as such) copy your materials then you
pop down the street and put the film through the 1 hour C41 and 'hey presto'
reverse text slides. When you buy the film the instructions are in the box and
you may change the background colors by filters, they list 9 in total. I make
lots of these slides and people just give me books or their printout from the
work and I copy them with the above setup.  
RM, lwells@kths.nsw.edu.au (L)
This is just what I have been doing these last couple of days. I started with a
computer but could just as easily have started by hand. All I did with the
computer was to make some black type titles for the slides I needed. 
I then copied these on a copy stand onto 35 mm Kodalith Ortho film. This may be
hard to find but possibly Technical Pan processed to a high contrast may also
work. You want to end up with clear letters on as black of a background as
possible. Copy the original black-type-on-white-background artwork with a 35mm
camera so that the letters appear in the locations you will want them in your
finished "blue slide". 
If you can't find 35 mm Kodalith Ortho you might try making single exposures
onto large size film that you've cut down to 35mm size and insert one at a time
into the camera. The large sheets are used in graphic arts houses. Or, they
could just copy the title slides onto the larger film using a Graphic Arts
camera and you then just deal with the reduction or size adjustment when you
make the combination exposure described below.
I then made an improvised slide copier placing my camera on a copy stand again
but installing below it a small light box to provide even illumination to the
slides that I was going to copy. The camera was a Canon A1 to which I fitted a
bellows with a 50mm Nikkor enlarging lens and adjusted the magnification to get
about a 1:1 reproduction. The film I used was Ektachrome 100 Plus. 
Next, with no slide on the light box I made a meter reading of the evenly
illuminated field. I then chose an exposure/shutter speed combination that
would yield three stops (8x) more exposure than that based on this condition. 
Theory being that the meter would suggest an exposure that would make the white
field a grey tone. I wanted it to be clear white so one needs to "overexpose".
I thought a three stop increase over grey would bring the white to an
appropriate, low, density level to make the letters look nice and white on the
screen. I then placed a title slide on the light box, adjusted its position to
fill the frame as planned and made an exposure. 
Without advancing the film I rewound the shutter (the A1 has multiexposure
capability) and placed a 47B (blue) filter in place of the B&W title slide and
made another exposure onto the same piece of film. It is important to note that
my meter was NOT used for determining the exposure for the blue background. In
fact, when I checked the exposure recommendation for the blue filter I found
that it was about three stops underexposed according to the in-camera meter.
Anyway, the outcome is that I have real nice white letters on a blue
background. BT, you could also do this using Vericolor Slide Film but I did not
have any of that around. The procedure with this film is a bit different also. 
Andy Davidhazy, andpph@rit.edu
... the film you want to use to create white letters on a blue background would
be Kodak Vericolor Slide Film SO-279...this film is specifically designed for
making transparencies (slides) from color negatives & internegatives and it is
also used for making transparencies with white text on different colored
backgrounds from a black & white original...according to the data sheet I have,
to make white text on a dark blue background you would photograph black text on
a white background with a #12 yellow filter on your camera and Kodak Vericolor
Slide Film SO-279 - for a cyan background you would use a #29 red filter on the
camera lens...the film is tungsten based for a 3200 K light source and is
processed in C-41 chemistry...if you have any more questions feel free to ask.
Bob Hendriksen / Freeze Frame Photography, AOL: Kingsnake
First we start with a kodalith of the image. (process in equal amounts of
Kodalith A/B developer) Using the kodalith negative as our original we use a
dupe setup to make two exsposures. 1st exp is for the type. 2nd exp is for the
blue background. We use Kodak 5071 dupe film. the exp is as follows f16 1sec
(type exp) 2nd exp f22/32 (Blue Background)                        
Should you have any questions please Email
Shaun, Camera Graphics Photolab, Albq. NM 87106, CDrisc9308@aol.com
Try Polablue by Polaroid. It requires a little experimentation but works
pretty well. 
You could try using Polaroid 'Pola Blue' but you'll need to get hold of the
processor too. The processor is a cheap plastic thing, but the Pola Blue
film is quite expensive over here. Hmm, pity you don't want to use a
-Steve Tristram 
I understand exactally what you need. We do this type of work daily for the
University of Maine. They are called Diazo Blue Slides. We use: Kodak SO-279
slide film (Catalog number 162-2364) This is a C-41 process Light the work with
4 100 watt light bulbs. Use a Kodak #22 wratten Gelatin Filter on the camera
lens. (catalog number 149-5571)                                  
This should be all you will need. Do your work on regular white paper with BOLD
black lettering and graphics. Try to stay away from thin lines and thin
lettering. If you have any other questions, we will be happy to answer them.
Steve Sleeper, sleepers@agate.net (Sleeper's Imaging Center)
I used to put black type on white background, and shoot this with vericolor
slide film and a lot of yellow filtration. This reversed the type to white on
blue. Poloroid makes a special poloachrome that does this as well.

Maxim, InstyOmaha@aol.com
===========================  end of section 34  ============================== 
                            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: