[photo-3d] Re: focus and convergence

[<donaldparks@xxxxxxxxxx>]

>    From: "Chuck Holzner"
> My son, who is 25, has good 20/20, can see far and up close without
> glasses, could not free view the picture.  I checked and rechecked
> alignment, rotation and window and kept trying to get him to see the
> depth with no success.  I then figured that he may have his
> convergence and focus linked and tried something else:  I had him put
> on my reading glasses and try again.  It worked.

    I'm also a believer that there is a link between focus and convergence distance that can be a source of discomfort when broken.  When I was younger I could not parallel free view.  I could relax my convergence to fuse the pictures but my brain
would not let me focus the near images while my eyes were converged at infinity.  My young eyes could easily focus on near pictures as long as they were converged at the same distance as the picture.  Now my older eyes can't focus that close.  I have
to wear reading glasses to make near objects seem to be at the distance my eyes are able to focus.  I can now parallel free view with relative comfort as long as I'm wearing my reading glasses.

      I went to a 3D Imax film recently that I believe was called "Into the Deep".  It was mostly underwater scenes that appeared to have fish swimming from 1 to 5 feet from my face.  Needless to say my eyes were strongly converged to follow these fish
swimming right in front of my nose for nearly the entire 40 minutes.  The polarization provided very good extinction so there was almost no ghosting and there was no vertical missalignment between the left and right eye images.  I found this viewing to
be very uncomfortable, however, because the true focus for the projected images was on the screen, about 50 to 100 feet away but my eyes were being forced to converge at only a few feet. -  Don

Dr. Donald J. Parks
Mechanical Engineering Dept.
Boise State University