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RE: 3d 2 perf transfer



Frank Smith wrote:

Does any one have any information on 3d transfers.  I have a client with 2
perf 35 that has the same image over itself slightly off set.  I would like
to end up with a 3d letter box.  The 2 perf makes the letter box
approximate cinemascope.  The spirit has a two perf setting and I have
considered two passes but I need some theory on 3d.  Thanks

3D or better known as Stereo transfers have been done in the past. It all
depends on what you want to accomplish. The original images were taken by a
camera with two lenses about 62.5 mm (2.4") apart to simulate the scene
each eye would see if you were the camera. Even though the images are
similar they provide information to the brain to compute how far away the
elements in the scene are. To display the stereo, and have it come out the
way it was intended, each image must reach the eye properly. Two images,
left and right, make up one frame.

If as you say there is one image above and one image below, and that
represents the left on top and right on the bottom then it is safe to
assume a 1.5:1 aspect ratio (a/r). This image would have to be letter boxed
as most monitors and display devices at this time are 4:3 a/r. If you were
to put this into the 16x9 a/r the letterboxing would be less.

Depending on which stereo system you are making this transfer for you would
have to contact the company whose display device you were going to use.
Some use alternate fields, field one being the left image and field two the
right image, and some use a higher field rate to reduce the 30 cycle
flicker. Computers scan at more than 60 Hz and are progressive.

To view the stereo images one must have either glasses which only allow the
left image to get to the left eye and the right image to the right eye.
This usually is alternating shutter glasses. For projection polaroid
glasses are usually the norm. There have been built some LCD projectors
with the poloroid axis at 90 to each other so that light loss in the
projector is minimal. There is also a lenticular process available but I
don't beleive it would work with video. There are other Blue/Red approaches
also but CCIR-601 color leaves a lot to be desired due to its lower
bandwidth color.

If you are only going to transfer the film to TV but not in stereo than all
that is required would be to only record either the top (left) image or the
bottom (right) image, not both. This would mean you would run the telecine
at the normal 4 perf. The images were taken about 2.5 inches ( about 1")
apart. If the spacing of the taking lenses were more than the standard
human interocular spacing then the stereo image would appear to be smaller.
With less interocular spacing the stereo image appears to be bigger even
though the camera hasn't changed position.

I have been dabaling in stereo for more than 40 years and have two Stereo
Realist cameras as well as a Stereo Lens for a Mitchel BNC that does a
similar trick of putting the two images onto the film. I hope this helps.
You can contact me at mailto:J_Mendrala at compuserve.com

You might take a look at http://www.stereospace.com/pdf/pdf.html for some
more stereo info.

Jim Mendrala
Real Image Technology, Inc.
805-294-1049 Fax: 805-294-0705

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