[3D Roundabout]

Last month we looked at edge violations and floating windows. I concluded that when viewing stereoscopic images on a small-sized screen, edge violations in negative parallax are something that must be considered, especially to the left and the right of the screen, and using floating windows can be a useful way to manage issues with objects exiting the screen unevenly and causing stereoscopic failure. This month, I will discuss interocular distance, miniaturisation, and convergence, and talk a little about focus.

Interocular distance (interaxial separation)

The amount of stereo effect is defined, in part, by the separation of the camera lenses, which defines the relative parallax differential between the left and right eye images. …

Miniaturization

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Convergence and Focus

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Conclusion

It is important to understand the effect of interocular distance on the perceived image. Too large, and it can cause strain in trying to focus or fuse the two images, as well as causing objects to seem excessively separated, elongated and miniaturised. Too small, and objects are perceived as being larger than they are in reality.

Where the intercoluar distance cannot be easily made smaller, it may be possible that setting the point of convergence further forward can help, but this will have the effect of lengthening objects and distances. This needs to be understood during shooting, because if changes are going to be made in post, the result can be unexpected when seen edited within non-effected shots. The reality is that it is next to impossible to ‘fix’ incorrect interocular errors.

Next month I will look in more detail at scene focus and viewing distance.

Steve Shaw is a Partner in Light Illusion, a top consulting service for the digital film market, with offices in the UK and India.

Read the full article here: http://3droundabout.com/2011/12/5774/the-basics-of-shooting-stereoscopic-3d-–-part-4-interaxial-distance-miniaturisation-convergence-and-focus.html