Practical Stereography
(last worked on: June 27th, 2020)
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"simplify, simplify"

This page attempts to anticipate the normal resources and questions of people trying to compose (3D) stereographs (aka: "view cards" or just "views"). It only presents 5 inch (wide) format stereographs since 7" format stereoscopes are expensive, while 5" 'scopes are give-away affordable --to purchase and to mail.

Stereography is an art form older than photography. Sir Charles Wheatstone had to draw stereo pairs by hand to illustrate his discovery and descriptions of stereo vision, since the invention of a practical camera was still a few years in the future.

Let's first get a grasp upon "the stereo window" --via Dr. Dale Hammerschmidt's illustrations --taken from "A Stereo Photo Glossary" (which see for any unfamiliar terms here). (Just skip ahead if you're okay with the window.)

It's surprising how hard this simple concept is to get across. Those who do understand the "stereo window" (and no special intelligence is required) --are (and despite their own initial problems) --consistently amazed at how hard it is for others to grasp.

What we have here is an over-head view of you --standing in a room --whilst gazing out of a rather small window. When trimming/cropping a stereo pair of images ---we try to replicate what each eye sees --though just such a window --onto the world. Each of the two prints in a stereograph corresponds to the view of each eye --the left-to-right extent of what each eye sees --through that small pane of clear glass.

Obviously: because of the different angle of each eye, they see somewhat different "takes" onto the world beyond the window --because the pane is near and the scene is far.

But we'll let Dale explain it to us:

* The Stereo Window (of a view): A basically simple concept that for some reason is not intuitively obvious, and causes no end of confusion to newcomers to stereography.  If one views a stereograph, it is generally most comfortable if it is mounted in such a way that one appears to be viewing the three-dimensional image as though through a window. This mythical window is the "stereo window."  If one does not mount stereographs in this manner, the edges often have a distracting "choppy" or "floating" appearance to them.  The way it works is outlined in the following figures, in what we hope to be an informative manner:

.
 

As you can perhaps appreciate from this illustration,
an object on the far side of the "window" will appear
to be more to the right in the right-hand image (that
is: have a wider margin on its left side) and more to
the left in the left-hand image (have a wider right-hand
margin). Just the opposite is true in an object which is
closer to the observer than the "window".  [end direct quotes]

~~~~~~~~~~~~~
When viewing through a window, the right eye sees a bit more to the left --and the left eye sees a bit more to the right. Trimming and mounting stereographs correspondingly will create an apparent "window" through which one views the scene. The most comfortably viewed stereographs are those in which all in the scene appear to be on the far side of the "window". Exceptions can be made for objects which appear to pierce the window pane, as long as they don't cut into the left or right frame edges.
~~~~~~~~~~~~

At left is an example of an object (the blob) which appears to be behind the "stereo window". (Use your small "finger lorgnette" or "free view" to see this pair.)

In life (as Dale's just told us), the blob appears further to the right --when looking with just your right eye. That's simply because your right eye is further to the right --and distant objects appear to "track" with one's moving point of view --much as the Moon "keeps pace with you" while driving along a straight road at night.

BUT: in picture pairs (designed to be mentally "fused" --seen, each, with just one eye) --this "window pane" eye-shift effect is simulated --simply by trimming the two prints inward on their outside edges --as might be needed* to produce the appearance of a close window. (* Real stereo cameras are designed to clip those edges off somewhat --right on the negatives or sensors.)

Why bother? --Because the picture pair has to stop SOMEwhere --and it might as well be done right --or else you'll get scene detail appearing to be cut away and floating in front of the window's frame edges, which results in visual confusion.
 

Here we see the blob again --but its clearly in front of the window, and yet: there's no problem in viewing it.

Reason: the object/blob doesn't cut the window's edges. It's "reasonable" that the blob can come through the window --as long as it doesn't tear into the window's frame by doing so.

If you measure the distance between the left and the right appearances of the blob (left edge of it to left edge --say), you'll find that this distance is less than when you measure the spacing between the same edges of each window frame. It's now the WINDOW which appears further away --because it appears to be more stationary when your vision shifts from your left eye to your right eye. (Sorry: this "window" explanation might be getting to the point of over-kill for you.)

(* If you've read this far w/o fusing the pairs, either stop and learn how to "free view" or order yourself up a stereo lorgnette. (Strong reading glasses might not work, since their prism power is inward.)

~~~~~~~~~~~~~~~~
 
 

--I've reduced the pairs here to an easily fused format.

This stupid looking drawing will help to avoid confusion when I refer to scene elements.

"Window Reversal": * Some critics will say your have "window reversal" if any subject matter is seen to appear in front of the stereo window. However, in this section we show how that can be reasonably done.

* Most people who know stereography will use that term if subject matter is seen to be "cut off" by the window. What that means is: there's an impossible relationship in which subject matter that's clearly (stereo-visually) in front of the window, is never-the-less blocked by the frame of the view's window --a window that appears to be further away --maybe even at the view's "infinity" or beyond.

The solution is to cut away the outer edges of the frame pair: some off the left edge of the left frame, an equal amount sliced off the right edge of the right frame. You can easily mask the pair first to see how much you need/want to remove.

"Infinity Separation": This is the actual (ruler) distance on the card between the same item in the farthest distance in both prints ( which details are called "homologous points at infinity").

Obviously, anything you're able to stereograph is less than infinitely distant, but anything more than 100 yards away is as good as "infinity" in normally stereographed views. "Hyper" pairs can reach out much further in conveying depth, but the separation of those distant points --as mounted on a view card, should still be at your "infinity standard" --for the kind of cards you're making.

When nothing approaching infinity is in the stereo view at all (an interior shot, say), you might want to set the furthest subject matter to less than infinity card separation --but that's not important.

In these illustrations, the Sun is a safe bet for stereo infinity, ya?

Normally, you trim a pair for a good "window" (defined by the two frame lines in my illustration --which represent the edges of two borderless photos), then mount them onto the card --such that the Sun-to-Sun distance is within some infinity separation tolerance.

For viewing a 5 inch card pair in a "V6" series scope (or just using its lenses as a "finger lorgnette"), the infinity separation can run from 2-3/8 to 2-5/8 inches (which includes a gap of maybe 1/8 inch).

So once you've selected your separation and gap, you've also selected your maximum print width.  The pair can be considerably narrower --often with pleasing results, but it can't be much wider. To maintain your (distant) separation standard, narrow print pairs will (of course) use a wider gap.

The height of the pair is up to you: whatever suits the subject and the card stock. (V6 series viewers for 5 inch format allow up to 3 inches --above the viewer's floor.)

The Window: You can imagine the borders/frames/stereo window of the prints to be just more scene elements, but ones that you can control through trimming and cropping. Here the corresponding sides (left to right) of the frame lines are closer in separation than all the scene elements except the ball --which consequently appears to come through the stereo window.

The stereo window/frame lines can be quite flexible:

The frame lines which describe the stereo window might be even be circles or ellipses. Obviously, computer graphics programs are better suited for fancy work than a razor knife, but the "spirit" of good stereography (IMO) doesn't seek to call such attention to itself. The stereo print pair "wants" to be a humble, graceful witness and window onto life.

Here's How:

--and here are the tools:


(click to enlarge)
You don't need the Scotch tape (that's 3M's "double-stick" on the right --good stuff) if you have a 2" wide roll of carpet tape (the plastic backed cheap stuff, not the fabric kind). (Carpet tape goes on first. Naked double-stick goes on last.)

Sticking out of the carpet tape is a "brayer" (as its called), used to spread ink, or to really wring two glued surfaces together --but you don't need that either. Just put a piece of stationery over the (protective paper peeled off) print and rub it down in place a bit.

* Trimming the carpet tape flush to the print edge is nice, but not necessary. 1/16th or so inside the edge works fine. Stopping very much short of the edges, however, might allow the prints to curl up. Definitely avoid wide interior tape gaps, which might result in the print buckling up.

If you free view, and especially when working with 5 inch format, you probably don't need those lens pairs ("lorgnettes").

Barely visible (under the break-away razor knife^ and pencil) is an 8 inch 30-60-90 drafting triangle. You need that --and a 12 incher too. For me, that thin, flexible, transparent, 6" shirt pocket ruler is a vade-mecum.

^ You want the kind of knife pictured --which is hard to find in stationery stores/departments now days, but 3 for a dollar at your dollar store. Straight away, make yourself a "sharps" disposal out of a coffee can and its lid --with a small hole in the middle.

The lorgnettes, knife, ruler and triangle are resting on a "cut-upon" mat. I've added a thick straight edge/stop, against which you slide the prints you're trimming and the drafting triangle. Everything here is resting on a large cut-upon (also with an added straight edge), which is really handy for cutting up paper stock to size.

Upper left we see a Walgreens print envelope, four 2x3 inch images on a 4x6 borderless print, and a 7 inch wide black card to mount a stereo pair of prints on (except that: the card should really be gray and 5 inches wide). (I was originally going to make this tutorial for both 5 inch and 7 inch wide views.)

* Get some "110 pound" (or so), 9 mil (or so), light gray "posterboard" or "card stock", then cut it down into 5x6 inch rectangles. (That's what the big cut-upon and triangle are for.) If you have to buy large sheets, maybe the (art supply) store has a large cutter.

* I've been using a desktop printer and white 8.5x11 posterboard --for printing the verso and the gray half of the 5x6. However, I've now found gray, 9 mil card stock at Walmart at 30 12x12 inch sheets (six in each of 5 shades) for $5.

Those reading glasses help a lot --even if you have young eyes.

* That blue thing is an inadequate corner rounder. It's just good enough to corner-round 9 mil photos, but maybe not after you've applied the carpet tape (peel-off protective paper still in place, of course). I normally use a tough old "Lassco Model 20" with a 3/8 in radius cutter, which costs well over $100. (It can corner-round 50 mil mat board.)

I bought a "medium" radius (about 5/16"), Fiskars brand corner rounder (because the "large" one wasn't in stock). It managed 24 mil and the folded 9 mil ("110 pound") poster board I'm using for this "Practical Stereography" project. (Yes: you really should have a good corner rounder.)

The next step is to get some stereo print pairs to work with.

You'll be "trimming and mounting" photo paper print pairs, using a razor knife^.

Take some "weight shift" pairs (or better yet: slide bar pairs)

--with an affordable digital camera or your cell phone's camera. Keep the two shots level to each other and homed against the slide bar. Resist the urge to "toe in" on the main subject. (That's for your eyes to do when looking at the finished print pair view.)

** If your camera has flat back and bottom surfaces, this slide bar (even if you just level it by eye) can help prevent toe-in/mis-aiming, different heights, and rotation between your left and right photos.

* Back-up shots are nice if you can easily match up the pairs afterwards. It helps to always take the left frame first, next the right frame, then take a shot of your shoes before taking another left-right pair of the same scene.

Next: get some "wallet size" prints of the selected left and right frames. (Walgreens lets you place four 2x3 inch frames onto their 4x6 inch borderless prints --via the "Edit"/"other" options when in the default "fill" and 4x6 mode. That wallet quad option occurs early in Walgreens' menu options.)

(1)

Apply carpet tape to the print back (leaving the peel-off paper on).
(That glove represents my left hand  :-)  --holding the drafting triangle, as I cut the tape flush to the print edge.)
 

(2)

Mark the left and right quads the same way on the backs: "L1, L2, L3, L4; R1, R2, R3, R4" --even though you won't
necessarily match them up that way. Then cut the wallet photos all apart on their 2x3 frame lines. (Don't be a
dummy like me --in this photo-- and try to finish trim two frames at once.
 

(3)

Pick a detail that's closest --like the lower right corner of that
shadow, and trim the right edge of both the left and the right prints to the
same distance from it (trimming the right frame just a tad closer to the shadow).
(Before trimming the right edges, ensure that you're leaving about 2-1/4 inches to the left edges.)
 

(4)

Measure over 2-1/4 inches to what will be the left edge of each print and mark with a scratch. Then trim the
left edge of each print to the scratch. (Big Stupid's at it again here --trying to trim two frames at once --per #2.)
(Yes: I'll eventually reshoot this instructional.)
 

(5)

Now the glove represents my right hand --holding the corner-rounded left print against
one last tool: a piece of 1/4" thick plastic --which is being held snug against the cut-upon's straight edge --in order to
space the (trimmed, ready, visually checked and peeled) print up from the bottom of the gray card. There's a faint
pencil mark at the center of the card, from which I space the left and right prints equally (by eye) for about a 1/8 inch gap.
Make sure that the card, the spacing tool and the print remain snuggly homed
against the guides --before laying down the print frame.

* Keep your work area/surfaces clean. Just a speck of dirt (or a cotton glove fiber) under a gloss print makes for an ugly looking bump.

* Commercial services like Walgreens returns you laser prints, so you don't need white gloves --just clean and dry hands.

(Hint: pick up an edge of the peel-off paper with your razor knife blade.)

The "extended legend" could be a printed 3x5 appliqué, or simply hand written (on a light gray 5x6 card).

(Again: I printed the whole 5x6 together this time.)

You can fold the "extended legend" over (becomes a "verso") or leave it straight up ("study card" style). If you fold it over,
do so precisely, then corner-round the view while folded, which gives it a nice appearance and simulates a traditional stereograph.
 

(6)

And there you have it.


 

Digital Stereography