[MF3D.FORUM:1051] Re: Mounting issue

["Dr. George A. Themelis" <DrT-3d@xxxxxxx>]

>Why, I would think this [convergence of the cameras]
>would be very very critical since its making the camera look 
>a bit cross eyed?  Could you explain why it's not critical..

Yes... if we are talking about a small convergence, then
it is not really critical.  The main danger is what is
known as "keystone distortion", the two images do not
match exactly and there is some vertical disparity which
might be seen along the edges (away from the center).

However, this distortion is small and in some cases 
people are willing to live with it because by converging
the cameras the stereo window is set at the point of
convergence.  This is true for 3d movies and video 
where there is no other easy way to set the stereo
window, then this is set by converging the cameras.

Another situation where this convergence is not easy
to avoid is when shooting hand-held hyperstereos.
Usually an object is centered at the viewfinder and
maintained between the two shots, which makes this
object the point of convergence of the lenses.

For general still photography where there is room to
set the stereo window during mounting, it is recommended
to have the lens axes parallel to each other.

It is very easy to align the cameras... After you put them 
on the bar, make sure that the center of the viewfinder of 
each camera is pointing to the same object at infinity.
(It is important that the object is far away because the
lenses will be converging to this object.)

When using longer lenses the problem usually is to align
the lenses vertically which is more critical than 
aligning them horizontally.  This is again done by making
sure that the same object is at the center of the viewfinder
(or same line of objects along the top and bottom edges).

George