Both rig types have their problems, and the decision the best rig to use is not always as obvious as it may seem...

The above image shows a Side-by-Side rig, where the main problem is the inability to get the interocular (interaxial) small enough for close-up work, making the Z-depth appear exaggerated, with objects appearing elongated and miniaturised - see Miniaturisation for more info on these problems.

A Mirror rig enables small interocular distances, so alleviating these problems.

But, the use of a mirror causes it's own problems as reflected light is naturally polarised, causing one camera to see polarised light, and the other not.

This polarisation on one eye will cause differences in the two eyes, with, for example, one eye seeing a reflection in a shop or building window, while the other eye will see through the window with no reflection. The fix is to place light polarisers on both camera lenses to equal them out, but with a corresponding loss in light...

Other problems are not so specific to the rig used, but show in different ways on different rigs depending on the cameras in use.

One serious requirement is for the rig to be very rigid, with no flex between the two camera mounting positions. One problem with inferior rigs, especially poor mirror rigs, is the cameras flexing as the rig is tilted, changing the comparative camera alignment. This can be a real problem as the change is dynamic as the rig is rotated and tilted, and not a fixed offset.

Matching lenses is a critical requirement, and no matter how hard one looks for matched pairs, there will always be some differences in colour, image alignment, size, etc., which will require fixing.

The way the separate camera bodies process the captured image can also vary, with the CCD/CMOS chip output not always being matched before entering the digital processing circuitry. Again, such variations will require fixing...

Contact steve@lightillusion.com for more info.