Lenticular Equations ala Nimstec

[P3D Grant Campos <gc6094@xxxxxxxxxxxxxxxxxx>]

Here's my synopsis:

According to the literature that Nimstec sent me, here is how to take
lenticular pictures with a slide bar or the like for Nimstec processing.

1. If film in the camera goes right to left or bottom to top, move the 
   camera from right to left after each shot.  If not, move it left to right
   after each shot.

2. Within the in-focus part of the picture (where there is fine detail and
   high contrast), determine the distance to the nearest object of interest 
   in the foreground, Df, the distance to the "center of attention" or key 
   subject, Dk, and the distance to the background (not necessarily 
   infinity, if it is not crucial to the photo), Db.

3. (I derived these equations by altering John B's maofd equation according
   to how they related to the tables Nimstec provided) (see acknowledments)
   Then use these equations to calculate the scan distance (the amount to 
   move the camera between each shot) using Df and Dk to get Sf, and using 
   Dk and Db to get Sb.   Then use the smallest of the two values, Sf or Sb.

   For Df and Dk in inches:  Sf = 0.0025 * Df * Dk * F / ((Dk - Df) * f)
                             Sb = 0.0025 * Db * Dk * F / ((Db - Dk) * f)

   For Df and Dk in feet:    Sf = 0.03 * Df * Dk * F / ((Dk - Df) * f)
                             Sb = 0.03 * Db * Dk * F / ((Db - Dk) * f)

   F = the standard focal length for the format:
       50mm lens for full frame 35mm film, 30mm for half frame 35 mm film, 
       80 mm for medium format.

   f = The focal length of the lens used.                                 

   Sb and Sf are in inches.

The total Scan distance according to the literature is Sf or Sb multiplied
times the total number of frames, n. 

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Acknowledgements

I'd like to thank Nimstec (for their 22 page "booklet"), Elliot S. (for his
encouragement and advice), and John B, (for his maofd equation) who in turn 
thanked, in temporal order, to Bob Mannle, Steve Spicer, and David Jacobson 
for their enormous help.

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Helpful Hints:

  They crop quite a bit so make sure you back up a little extra (5-10%)
to make sure your desired composition will be in the final print.
  
  Try to avoid extremely high contrasts like a dark pine tree against a 
bright sky.  It would cause ghosting. 

  Try to leave a blank frame between each frame series.

  Try to compose your picture with discrete diferences between depths like
a line of tree trunks, not like a rope going from the foreground to the
background.                     

   There are many more hints, but for brevity I'll stop here.

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Technical Tidbits:

The most limiting factor is the maximum on-print deviatioon which is called
"jump", or "flip", or "scintillation".   Nimstec suggests 1/2% of the width 
of the print as a max. (This doesn't fit with other info to me, but I'm 
still thinking).

The lenticular screening that Nimstec uses puts all the frames you took 
within 32 degrees of view.  In other words, if you took 8 pictures to make 
the lenticular, when you close one eye, you will see a new image every 4 
degrees. Or if you used 16 images, the image would change each 2 degrees.  
So, at a distance of 13 inches (330 mm), Dp, looking at a 8 image print, 
your left eye will see image number 1 while your right eye sees image 
number 2.                     

    Distance between the center of each image, Cd, is as follows:
    Cd = 32 * pi * Dp / (n * 180) or in this case 23 mm

    So while your left eye sees the middle of image one, your right eye is
    seeing somewhere near the middle of image number 2.        

And at that distance, while one eye is scanning from left to right of a 4"
wide print, it moves through 17.6 degrees, so you will only see one image 
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I'm still trying to come up with my own equations based on the technical 
tidbits, and taking into consideration, ortho viewing, avoiding squash and
stretch, and the limitations of the lenticular screens.

Hope this helps.

Grant Campos
mailto:gccampos@xxxxxxx


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