Stereo windoz

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

I don't know who wrote what or even what they meant when they said it, 
anymore.  But do you think that would keep me from commenting on what 
I _thought_ they said?  Guess again.  8-)

>> This relates to the reality of looking through a real window.  Stand 
>> in front of one in your home.  Close one eye and look.  Then close the 
>> other eye and look.  The right eye saw more of the left side of what 
>> was out the window and visa versa for the left eye.

> Right.  Keep in mind, though, that the angles of view of your two eyes must
> converge and cross _at_ the window in order for the effect you describe to
> occur.  This is true regardless of whether your eyes themselves are
> converged on the window or not. 

I'm confused by this.  It seems like at first we're saying that you have 
to cross your eyes when you look out a window in order to see more of the 
right side of a scene with the left eye than with the right eye.  That 
wouldn't be true because if you looked at an object at infinity, you'd 
see more of the right side of the scene with the left eye.  The next 
sentence seems to reverse the prior statement.  Anyone care to help me on 
this?

> I guess what I have a problem with is your use of the phrase
> 'converging angles of view', which seems to imply some kind of angular
> rotation, when there is in fact none.  Yes, it is a matter of semantics,
> but sometimes the choice of semantics makes things much easier to
> exlain to a neophyte.  I prefer to think of the offset as a selective
> masking at the film plane.

I think "toed-in" is definitely confusing, but to the cognoscente rather 
than to the neophyte.  The cognoscente has read "The World of 3D" and 
similar books which use "toed-in" and "convergence error" to mean taking a 
pair of cameras and making their axes cross at the window distance or doing 
the same thing by taking one shot and then moving the camera and taking 
another shot such that effectively you've done the same thing.  Or by using 
a rotating or rocker table to get the two views.  I think "converging angles 
of view" would be in the grey area because it could easily mean "toed-in" 
although that's certainly not what was meant in this case.  That's why I 
used a long and clumsy passage to describe what I meant.  So what's a good 
way of saying this that's not 15 words long?  We always say window distance 
but that's because we know what window distance is predicated upon.  What 
if you don't know?  What then is a good phrase?

John B


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