Re: silver screen

[bercov@xxxxxxxxxxx (John Bercovitz)]

Steve Spicer said his silver lenticular has 16 lines per cm or 
40 lines per inch but that a coarser version is also around.  I 
called a friend and his is the coarser version.  It has 10 lines 
per cm or 25 per inch.  

I'd like to know at what distance the lines are visible under 
actual viewing conditions.  Could some of you folks shine your 
projector on your screen with an empty slide mount in the 
projector and while wearing your polarized glasses, walk toward 
the screen until the lines just become visible?  I need to know 
that distance.  Please also tell me which number of lines per 
whatever you have.  If I had a few distances at which lines just 
become visible, I could figure what size screen is needed under 
what conditions.  Sample calculations follow.

Thanks,
John B

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Visual acuity varies from individual to individual and also under 
various lighting level and contrast conditions.  The best eyesight 
with enough light and enough contrast is around 1/2 minute of 
angle.  Normal eyesight is around 1 moa.  Normal eyesight with 
dimmer light or less contrast is around 2 moa.  What do we have 
under viewing conditions?  I don't know and that's why I'm 
requesting tests.

       Minimum seating distance from screen to avoid seeing lines
lines      
per inch  1/2 moa eyesight      1 moa eyesight      2 moa eyesight

  40      14' 4" (4.4 m)        7' 2" (2.2 m)       3' 7" (1.1 m)
  25      22'11" (7.0 m)        11'6" (3.5 m)       5' 9" (1.8 m)

The average stereo camera's lenses are about 36 mm.  The 5-perf 
format has an aperture height of 23.5 mm and the 7-perf format has 
an aperture width of 28 mm.  If one matches left edges of 
projected images (I'm not endorsing the practice, only using it 
for calculation) then the correct screen width for 5-perf viewing 
will be 23.5/36 times the minimum seating distance given above.  
Similarly for 7-perf viewing, the correct screen width will be 
28/36 times the minimum seating distance given above.  To reduce 
the table to two dimension so it will fit on a piece of paper 8-), 
let's just assume for a moment, probably incorrectly, that the 
visual acuity is 1 moa.  Then:

             Square screen width and height
lines      
per inch    5-perf format         7-perf format

  40         56" (1.4 m)           67" (1.7 m)
  25         90" (2.3 M)          107" (2.7 m) 


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