Personal Work - Stereoscopic 3D Filming (excl. Post-Production)

Interaxial Separation between lenses

The interocular separation refers to the distance between the centers(pupils) of human eyes.  This distance is usually expected to be an average of 65mm for a male adult.

Similarly, interaxial separation is the distance between the centers of two camera lenses (the entrance pupils.) The human interocular separation is an important constant stereographers use to make calculations for interaxial separation.  Beware that Interaxial separation is often incorrectly referred to as “Interocular” and vise-versa.  In the professional world of  stereoscopic cinema it has become the norm to refer to interaxial separation as “i.o.” even though it is the incorrect term.

Binocular Vision, Retinal Disparity and Parallax

Eyeballs converged on center object

Binocular Vision simply means that two eyes are used in the vision system.   Binocular Vision is very important to most mammals (including humans) because it allows us to perceive depth at close range.
Try this:  Hold one finger next to your ear.  Now stretch your other arm out straight and hold up another finger.  Now bring your two fingers together and touch the tips together.   Is was easy right?  Now repeat the same procedure but close one eye.  Were you able to touch your fingers together on the first try?  Now you know how important binocular vision is at close range.
When we look around at objects at different distances from us the images of those objects will be projected on our retinas in slightly different locations for each eye.  Our brain can interpret this “Retinal Disparity” and help us determine depth.
When we shoot 3D with two cameras from slightly different  positions the same thing happens;  each camera’s sensor registers the objects in the scene in slightly different horizontal positions.  We call this difference “parallax.”

Convergence & DivergenceBinocular Vision and Parallax are the primary visual tools animals use to perceive depth at close range.  The wider an animal’s eyes are apart (its interocular distance) the deeper its binocular depth perception or “depth range.”

At greater distances we start to use monocular depth cues like perspective, relative size, occlusion, shadows and relation to horizon to perceive how far away objects are from us.
Of course it would be difficult to look at double images all day so instead our eyes naturally angle in towards the object of interest to make it a single image.  This is called convergence.

Converged Eyes

Here’s an example of how your eyes use convergence in the real world.  Hold a pen about one foot in front of your face and look directly at it.  You will feel your eyes both angle towards the pen in order to converge on it, creating a single image of the pen.  What you may not immediately perceive is that everything behind the pen appears as a double image (diverged.)  Now look at the background behind the pen and your pen will suddenly appear as two pens because your eyes are no longer converged on it.  This “double-image” is retinal disparity at work and it is helping your brain determine which object is in front of the other.

Diverged Eyes

What never happens to your eyes in the natural world is divergence, which would mean that your eyes would angle outward.  This is because the furthest point you could possible attempt to look at is at infinity and even infinity would only require that your eyes be angled perfectly parallel to each other.   This is why stereographers should avoid background parallax values in their scene that may require the eyes to diverge when viewed.  This is easy to keep in check through some simple math but we will cover that a little later.

Simply put, the “Stereo Window” refers to the physical display surface. You will be able to visualize the concept if you think of your TV screen as a real window that allows you to view the outside world.  Objects in your stereoscopic scene can bebehind or outside the window (positive parallax,) on the window (the Screen Planeor zero parallax,) or inside, between you and the window (negative parallax.) 

If an object’s left image is to the left of the corresponding right image then that object has positive parallax and will appear to be behind the screen.

If an objects left image is to the right of the right image then it has negative parallax and will cause your eyes to cross, which will suggest to your brain that the object is in front of the screen.

This is the basic principle behind stereoscopic shooting and emulating human binocular vision with two cameras.

There are special stereoscopic lenses on the market designed for various digital SLR cameras.  These lenses will work with a single camera but capture a left and right point of view in the same frame.   The concept is intriguing but the lenses are very slow (F/11 – F/22), they use a smaller portion of the image sensor for each eye, they are usually made from plastic optics instead of glass and (in the case of the Loreo) the aspect ratio is vertically oriented.

Left Eye Presented View versus Right Eye Presented View (exaggerated separation for demonstration only)

Perceived Position relative to Stereo Window

Images and information came from:

http://www.dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/

And is posted purely for something to look back at for information i may forget.