T3D Re stereo math

[aij.klooswyk@xxxxxxxxx]

Tom Deering wrote:
>I visualize 1.2mm of onfilm deviation as being related to the amount of
>convergence the eyes can comfortably do.  Would it be just as correct >to >measure it as an angle?  And is that why the 1.2 mm is actually >f/30?

Not so long ago I wrote to P3D: THINK IN ANGLES.
This obvious didn't pass Tom's filters, can think of 3 reasons: 
1. the posting was long, 
2. it used capitals, 
3. it contained a horrible ASCII-drawing.
In Germany for a long time not 1/30 but 1/50 was the Law. 
It was called the 70-Minuten Bedingung (70' condition). 
I don't tell why, read my posting :-).

John Bercovitz:
>(...) all people can tolerate a total on-film deviation of 1/30th the
>focal length and most people can tolerate 1/15th under decent >conditions.  (I'm using >"focal length" loosely here.  When you shoot a 
>closeup, you move the lens away from the film so the "focal length" 
>increases for the purposes of this calculation.)

Here one of the presumptions from maofd.txt is repeated. It is false.
When you use the same mounts, projector, screen, viewers for macro as
well as for other slides, making shows mixing slides and so on, it is
obviously erroneous to use a doubled on film deviation when shooting 1:1
macro's, in which the working focal length is doubled.   The maofd
theory seems to ignore viewing :-). 
Mounting and projection system should be defined before spreadsheets are
designed. I'm working on longer text that will discuss maofd. (I'm not
used to the chatting effect of these lists and prefer more systematic
discussion)

In the mean time, read George Themelis:
>The significance of the 1.2 mm comes in projection. 

Jim Crowell wrote:
>Actually, it's a function of the fusional range of the visual system, 
>i.e. the amount of disparity (difference in position of a feature 
>between the two eyes' images) that the brain can merge into a single 
>image.
>(..) To oversimplify  :-).
>(...) As I think Boris pointed out on that other list, it may also be 
>affected by the magnitude of the disparity gradient.

Oversimplification can hardly be avoided in necessary short postings.:-)
"Fusional range of the visual system" seems just a longer way to say: viewable.
I'm sure Jim Crowell could tell us more about the
convergence-accommodation relation or about accommodation induced
convergence, which contribute to the system he mentions.
One of the pupils of the 19th century ophthalmologist Donders (inventor
of the letter cards optometrists use) wrote a thesis (in Latin!) on the
convergence-accommodation relation. The large number of publications on
that subject till now can only be judged by specialists in the field.
But who is Boris?
 
John Bercovitz again:
>I don't know why hand viewers are 
>easier but it's common knowledge (and readily observed) that they are.

My theory is that masking off the lateral field of view in hand viewing
is most important, probably enhanced by relatively high luminance.
In projection the screen image necessarily is less bright, and pola
filters cut more light. The projection room is inevitablely lit by the screen, so is noticeable in the perifery of the visual field.
This is a theory which could be tested for example by deteoriation of
viewer images. I have not done it yet, altough I have had this theory
for some time...

I hope I have not offended anyone by being brief or using peculiar
English, I have learned that tempers sometimes are inconstant on these
lists :-). I appreciate also the ideas which I oppose to.

Abram Klooswyk               (abram.klooswyk@xxxxxx)



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