Re:SIRDS and Interpupillary Distance

[P3D Norm Goldblatt <normgold@xxxxxxxxxx>]

Interpupillary distance is about 60-70 mm for 90% of the adult
population.  Most SIRDS at their original size have a 'pitch' of about
30-40 mm precisely so that the eyes, even when close set, have to
converge slightly. So, the 'Asian Effect' is highly unlikely.  A 40 mm
IPD would look mighty wierd- hardly enough room for your nose!  
The top 3 reasons for not being able to see SIRDS (beside the obvious
ones- cyclopia, strabismus, low IQ-(just kidding))

1. The picture is not clearly in focus. It's amazing how many farsighted
people try to look at SIRDS without their glasses. Suffering age-related
presbiopia myself, I have found it virtually impossible to make out the
hidden image unless I am wearing the right glasses for seeing at arms
length. This is NOT true for stereo pairs.
If a person is wearing bifocals, it is usually a little awkward to look
down through the 'reading zone', but they must. Even astigmatism, if not
corrected, makes viewing SIRDS difficult.

2. Folks who have never been able to see the image don't know what to
look for. The proper convergence is probably just passed right over. 
3. Tilt is intolerable- just a 1 or 2  degrees and it becomes either
painful or impossible to converge properly. Viewer should take measures
to make sure both head and picture are horizontal.
Norm-
http://www.aimnet.com/~normgold


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