P3D Mounting Stereo Cards

[koganlee@xxxxxxxxxxxxx]

	This is a response to the discussion on mounting stereo cards. When I 
began doing stereo photography in 1984 I seldom showed anyone any of the 
images. For the most part, I made medium format negatives for which I made 
contact sheets, but seldom made any finished images. After about 6 years of 
doing this, I discovered (in 1990) the Stereo Society of America and joined 
one of the print folios. This meant I would have to make stereo cards. I'd 
never made a stereo card before, so I was somewhat daunted by the prospect 
of making a card and presenting it to a group of experts. I could find no 
information on making stereo cards per se, so I got information about the 
stereo window by reading about the mounting of slides from "The World of 3-
D" by Jacobus Ferwerda (has been available from Reel 3D) and got the 
dimensions by looking at the antique cards that I had. Since I was doing a 
lot of commercial color printing at the time, it was almost as easy to make 
40 prints as it was to make one, so that is what I did. When it came time to 
mount it though, I was frustrated by having to painstakingly measure and 
trim the prints, let alone try to figure out how to adhere them. It must 
have taken me over an hour to make the first card. I knew that if I were 
going to do this on a regular basis I was going to have to figure out an 
easier way, probably using some sort of jig. I assumed the SSA members would 
have all these things figured out already and anxiously awaited the first 
folio of cards. When I got the folio I saw that about half of the cards were 
made with Q-Vue masks, which produce a pleasing result used with Grand Photo 
prints (applause for the technical expertise of Craig Daniels). The rest 
were hand done, but most were not particularly precise. I soon realized that 
they were in the same boat I was. No one mentioned that Bill Patterson and 
John Dennis had written articles on making stereo cards and I still have not 
seen those articles. When I became secretary of one of the circuits in 1991, 
I decided to write an article on the mounting of cards, for the benefit of 
new members. In it I describe various pertinent dimensions, how the stereo 
window works, and how to make jigs so that trimming is much easier. (It now 
takes me about 5 minutes to mount a stereo card using these jigs.) I also 
discuss mount boards and adhesives. I have condensed this article for this 
message and have left out the graphics since I don't know how to put them in 
an e-mail messaage.
				Mounting Stereo Cards
	Generally, the size of a Holmes stereo card is 3‡" x 7". The corners 
can be left square or they can be cut round (using a Lassco corner rounder 
or other means). As for the material, a 4 ply acid-free mat board is 
preferable. Several companies make them, including Bainbridge, Crescent, 
Rising, and Strathmore. Virtually any color can be found in acid-free board, 
but I would suggest a color which is less saturated than the colors in your 
image, so that it does not draw your eye from the image. The space between 
the two halves can vary between no space for most of the antique cards to 
about 1/8" or even more in some cases. One-sixteenth inch seems about right 
to me.  
	The width of each chip should not be more than about 3". The exact 
maximum width, though, is limited by the infinity separation which is 
determined by the lenses of the stereoscope. (The stereoscopes I measured 
had parallel infinity points about 3-3/8" apart.) So the maximum infinity 
separation for these viewers would be 3-3/8" (or 85mm) before the person 
viewing would have to diverge their eyes. I prefer to use a more 
conservative 3-1/4" (or 82mm) maximum infinity separation for my own images. 
If the difference between near points and infinity points is 3/16" (I 
discuss this more later), the width of the chip is 3", and the space between 
the chips is 1/16", that makes a total infinity separation of 3-1/4".
	The process of obtaining a stereo print of the right size is a problem 
that is not easy to work out. If you print your own you can try different 
enlargements until you get exactly the size you want. If you're using a 
Realist you can have prints made by Grand Photo or some other lab which is 
used to making stereo prints. If you're using twin 35mm or medium format 
cameras and not printing your own, you will have to work with a lab to get 
the size you want. Most of the twin camera users I know (including myself) 
who are making stereo cards are printing their own images.
	After one has obtained a stereo pair of the right size, it is ready to 
be trimmed and mounted. The simplest way I have found to do this is to make  
3 jigs. The first jig is for trimming the tops and bottoms. Cut (or have 
someone else cut) a piece of glass 3" high (or whatever height you have 
chosen for your images) and about one foot long. Make sure it is exactly the 
same height from one end to the other. Cut it in half, so you have 2 pieces 
about 6 " long. Cut pieces of mat board bigger than the pieces of glass and 
tape the glass to them so that the end of the glass can be lifted and the 
image placed under it. To trim the tops and bottoms simply place each chip 
under its piece of glass and maneuver them until they are in the same 
relative positions with the edges of the glass. Take a thin razor blade and 
trim the top and bottom edges carefully. I have left out some of the details 
here, if you can't figure them out, e-mail me and I will send you the 
detailed plans.
	To trim the sides you will need another jig. Cut a piece of glass 
about 3" wide (the exact width will depend on the width your images will 
normally be, mine are 2-15/16") by about 6" long. You will tape it to a 
piece of mat board in a similar manner to that of the previous jig. The 
major difference is that you need a method of trimming the image exactly 
perpendicular to the top and bottom edges. To do this glue a piece of 
photographic paper under the glass where the bottom of the image will lie, 
making sure that the edge of the photographic paper is exactly perpendicular 
to the edge of the glass. To trim the chips, place the left one under the 
glass so that the bottom is against the photo paper and the right edge is 
positioned where you want to trim it. With an ultra fine-point Sharpie pen, 
make a mark on the glass at the near point of the image. Then trim the edges 
with a razor blade. Next place the right chip under the glass so that its 
bottom is against the photo paper and its near point is under the pen mark. 
Trim the edges. That's all there is to it. By carefully marking the near 
point of the first chip and carefully placing the second near point under 
it, you will cause the near point to be at the stereo window.
	Now mount the image. First one must consider the adhesive. One could 
use dry mount tissue, glue, or Positionable Mounting Adhesive (by 3M), which 
I recommend. The adhesive (except for glue) should be applied before 
trimming. In order to position the images on the mount board, you could make 
pencil marks on the mount or you could make a jig to help you quickly 
position it. I will leave this jig to your imagination. If you want details 
I will be happy to send them to you.
 
	Now I will describe a simple way to analyze whether a stereo card has 
been mounted with correct window placement. (If you read this article 
without actually doing it, it will seem more complicated than it is.)
	Start by taking a sheet of letter size paper (a 5 x 7 file card also 
works well). 
1) Place the top edge of the paper at the bottom edge of the stereo image 
(the stereo card should preferably have a plastic sleeve to protect it). 
2) Using a pencil, make a light mark on the paper at the left edge of the 
left chip. Label this A. 
3) Make another mark at the left edge of the right chip. Label this B. 
4) View the image in a viewer and make a mental note of where the near and 
far points are located. 
5) Place the edge of the paper so that it runs through the near points with 
the A under the near point on the left chip.
6) Make a mark on the paper at the near point on the right chip. Label the 
mark C. (It should be at, or very near, B.) 
7) Place the edge of the paper so that it runs through the infinity points 
with the A under the infinity point on the left chip.
8) Make a mark on the paper at the infinity point on the right chip. Label 
the mark D.

Analysis of the window position.
	Let us first assume that you do not want any part of the scene coming 
through the window. (I will consider the case of something coming through 
the window later.) Point C (the near point in the right chip) should be 
right on, or slightly to the right of B. If C is to the left of B, then you 
have a window reversal. If C is more than slightly to the right of B, then 
the window is farther in front of the scene than necessary, and you will 
have more disparity on the edges (also known as "floating edges") than 
necessary.
	If the card has already been mounted this will be the end of the 
analysis, but if you haven't adhered the chips yet, this analysis will tell 
you what to do next.
	If B and C are together, you have a perfect window and don't need to 
make any changes. 
	If you have a window reversal (C is to the left of B), then measure 
the distance from C to B, and trim that amount from each of the outside 
edges (erring on the side of trimming too much). If you are using a Q-Vue 
mask then you do not need to trim, but you must get a narrower mask.
	If C is more than slightly to the right of B and you want to place the 
window closer to the scene, then measure the distance from B to C, and trim 
that amount from the inside edges (erring on the side of trimming too 
little). If you are using a Q-Vue mask you will need a narrower mask in 
addition to trimming.
	If you have something that you want to appear through the window, 
simply decide where you want the window to intersect the scene and make that 
point C (instead of making the near point C). Do everything else the same.
	The distance between the two chips will affect the viewability of the 
image, but will have no effect on the window position.
	Also, be sure that you have located the actual near point. In some 
complex scenes there are weeds or other objects that are closer than is at 
first obvious. This throws off the window position.

Analysis of depth
	The analysis of depth involves the amount of deviation from the near 
point to the infinity point. Simply measure the distance from C to D. This 
distance should ideally be in the range of 1/8 to 3/16 inch. If it is less 
than this the scene will probably appear to be flatter than it optimally 
could. If it is a little greater than this the scene will start to appear 
less smooth and as it continues to increase it will cause eyestrain in the 
person viewing it. Why this distance would be lesser or greater depends on 
the lens or camera separation when making the exposure, the focal length of 
the lens, and the amount of image enlargement. I will be happy to discuss 
this with anyone who inquires.
	The other useful information one can obtain from these marks is the 
distance between the infinity points. Measure the distance between A and D. 
As this dimension exceeds about 3-3/8" (depending on the viewer) the image 
will become progressively harder to view without eyestrain. 
	These suggestions are based on my experiences printing and mounting my 
images, observing the images of others in the Stereo Society, and discussing 
these things with other knowledgable stereo card makers. This is not 
intended to be the final word on mounting stereo cards, but as an aid to 
someone who has questions about making stereo cards. If anyone has 
additional questions about any of this, I will be happy to anwer them by e-
mail, regular mail, or by  phone.

David Lee, koganlee@xxxxxxxxxxxxx
3664 Hardin Way, Soquel, CA 95073
408-476-0702




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End of PHOTO-3D Digest 2434
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