[3D Roundabout]

Last month we looked at Interocular distance, miniaturisation, convergence and focus. I concluded that too great an interocular distance causes eye strain, elongation and miniaturisation, whereas too small a distance causes objects to appear unnaturally large. I also looked at the effects of different convergence and focus settings. This month, I will discuss the cut-out effect, scene focus and viewing distance.

The cut-out effect

While there is a certain amount of disagreement on the issue of the cut-out effect – mainly to do with terminology and the individual’s concept of the image that is being looked at, in general terms, the cut-out effect is when planes of objects seem unnaturally separated, as if they appear in separate layers like cardboard cut-outs stuck at different distances.

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Conclusion

Using long lenses to provide close-ups on distant objects is often unavoidable, but it will result in image foreshortening. However, while it is tempting to increase the interocular distance in order to compensate for this, as I have shown in the above examples, this can in fact make the problem worse.

The issue of focus is even more important with objects in the foreground, as these are closer to the viewer, and the brain knows that these should be clearer than images further away. However, focus can be used to guide the audience to specific locations within the image, as demonstrated on a number of occasions in Martin Scorsese’s film Hugo.

As also shown above, the ratio of the viewer from the screen, based on the screen size, needs to be understood in determining the amount of stereoscopic effect that will be apparent. Again, there are all sorts of calculations for this, but as was stated at the beginning of this series, our industry is about the image, not about strict mathematics!

In my final part of this series next month, I will discuss projection and displays, and headache-inducing problems.

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

See the full story here: http://3droundabout.com/2012/02/6467/the-basics-of-shooting-stereoscopic-3d-part-5-the-cut-out-effect-scene-focus-and-viewing-distance.html?