T3D Re: Different focus points for each lens

[erker@xxxxxxxxxxxxxx (Greg Erker)]

>I have not seen a discussion of this method/effect on P3D or T3D and
>could not spot it in the archives (try searching on 'focus' and I
>get many hits).  Comments?

  If you have a good stereo camera the lenses are
matched in focal length. This does two things: it
makes them track together as you focus in and out,
and they both produce the same size image on film.

  So lets say that you have two cameras with (exactly)
80mm lenses. Leave one focused at infinity and
move the other out to 81mm. The focus of this one
is now at about 6.5 metres. The problem is that
the two images on film will be about 1.25% different
in size. Not a huge amount, but above the 1%
maximum missmatch that you sometimes hear about.

  So ideally you would have lenses of slightly
different FL to produce the same size images on
film when focused at different points.

Greg E.



------------------------------