Re: [photo-3d] focus and convergence again

[John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>From: "ron labbe" <ron@xxxxxxxxxxxx>
>Subject: [photo-3d] focus and convergence again

[Other JR]
>JR writes:
>>>I would agree that focus and convergence are usually coordinated functions
>in that they usually occur simultaneously and by similar amounts, but they
>certainly aren't "linked".

>To make this more obvious, consider the situation of "synchronized
>swimmers".  Their actions may appear to be identical, and they are
>performing in the same medium (water), but it would be incorrect to state
>that they were "linked".<<

>I can't agree with this (OBVIOUS?) comparison at all! The two swimmers are
>consciously making an effort to coordinate their efforts, but one does not
>have to consciously focus their eyes at the same time they are converging.
>One goes through the three dimensional world with those two eye functions
>NORMALLY LINKED: when you look at something far away, your are focussed AND
>converged far away. When you look at something close, you FOCUS and CONVERGE
>on something close. This is normal and as unconscious as breathing. Of
>course, they CAN be unlinked! But the only time I can think of when they
>ARE, is for the stereoscopic illusion of three dimensions, when you are
>focused at one place, but converged at any distance... when else?

This JR agrees with Ron. When I was learning to free-view stereo, I
had to work to consciously decouple convergence and focus. Having done
a lot of viewing of stereo photos, the decoupling now *seems* natural,
but it wasn't to start with. I believe most people who have not viewed
stereo images (who have normal vision) have a default coupling between
convergence and focus, which requires an effort to override. Even after
the decoupling is learned, there are still conflicting depth cues being
received by the brain, and for some people it may require further pracice
at ignoring the focus cues, until stereo based on disparity cues alone
can be interpreted as natural-looking stereo.

John Roberts