There are two main approaches to shooting stereoscopic images with two cameras; converged or parallel.

The main difference between the two is that shooting converged reduces the amount of post-production potentially required to make the image viewable, but with the danger that the introduction of excessive parallax (having the left and right eye images too far apart from each other) can make the image virtually impossible to see throughout its depth range.

Shooting parallel means it is all but impossible to have excessive parallax, if the inter ocular distance is not excessive, but with the need to horizontally re-position the two camera images in post to set the desired screen plane (zero parallax) position.

For example the following image is the natural result of shooting parallel, with no post-production re-positioning.

Here all the image is in front of the screen plane as the whole image has negative parallax (the left eye image is to the right of the right eye image).

For situations where the image is to be viewed on a 'normal' sized theatrical screen, or monitor, this negative parallax causes a lot of problems, as the image appears to be 'cut' by the screen window, when the perspective of the image suggest it exists in front of the screen... This is due to one eye's image being cut-off before the other eye (see Floating Window for more info on this).

When viewing on a far larger screen, such as IMAX, this is not a problem as the screen edges are outside of the viewer's normal field of view, so the issue is not seen by the viewer, and parallel shooting is the standard for IMAX projects.

The following image shows the same parallel shot material horizontally re-positioned in post to place all the image behind the screen window.

For smaller screen sizes this is a much easier image to see, and reduces dramatically the likelihood of induced headaches!

The above images also go a long way to help explain the differences between negative and positive parallax, and the position of the image relative to the screen plane!

Next Page - Screen Window

As always, test before committing to a particular style of stereoscopic 3-D shooting.

Or better still, contact steve@digitalpraxis.net for more info.