Re: Silver screens

[bercov@xxxxxxxxxx (John Bercovitz)]

Michael Kaplan writes:
 
> I just received my Da-Lite Super Wonderlite screen and set it up next to
> my older Da-Lite Silver Pacer. As most of you know, the SWL has 40
> vertical lines per inch, while the old Pacer has 25.
> 
> I projected a stereo image that had a large white area in it, using a TDC
> 116 at a distance of 12 feet from the screens, which were set up side by
> side. Viewing the image, split over 2 screens, with glasses, I noted that
> the lines on the SWL became visible at about 7 feet from the screen,
> while the lines on the old Pacer became visible at about 12 feet.
 
Well, from this we know Michael can consistently see 1 minute of arc even
under these not-so-favorable conditions.  If we assume other folks have
similarly good vision, we can make some statements about minimum screen
size for different applications.  A minimum screen is a screen big enough 
that when you're sitting at the correct place, you're sitting far enough 
back from it that you can't see the lines in the screen.
 
The ortho seat has a cousin in flat slide projection and that is the 
center of perspective.  Its position is calculated in _exactly_ the same 
way as the position of the ortho seat is calculated:
 
Distance to the best     camera lens focal length
seat in the house    =  --------------------------  times screen width
                              format width
 
Let's call (camera lens focal length / format width) "k". 
 
                                                  25 line/inch    42 line/inch
camera       lens focal   format width     k         screen.         screen.
             length                               min width, ft.  min width, ft.
 
flat photography - 
 
35 mm SLR     35            35.5          1            12               7
35 mm SLR     50            35.5          1.4           9               5
35 mm SLR     85            35.5          2.4           5               3
 
stereo photography -
 
5-perf        35            21.5          1.6           8               4
7-perf        38            28            1.4           9               5
twin SLR in   50            28            1.8           7               4
7-perf mount
 
Since I won't get anything less than the 42 line/inch model unless someone
offers me a deal that is too good to pass up, and since I'm willing to forgo
the pleasure of correctly viewing SLR slides shot with a 35 mm lens, I can 
squeak by with a 60" screen but what I'd really like is a 70" screen.
 
Da-Lite told me on the phone that all of their silver lenticular screens are 
now 42 lines/inch.  Should I believe them?  
 
Looking in B&H, for 70" screens I see a Picture King for US$165 and a Model B 
Deluxe wall or ceiling mount screen for US$129.  The Pacer only goes up to the 
50" size, not big enough to hide the lines under all conditions of usage.
 
In the 60" screens, the Picture King is US$148 and a Model B Deluxe wall or 
ceiling mount is US$109.  Going to this smaller size hardly seems worth the 
$20 saved.

Any comments before I talk to she-who-must-be-obeyed about committing such 
sums?

Thanks,
John B


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End of PHOTO-3D Digest 14
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