P3D Re: Graphic's "Depth Master"

["KENNETH LUKER" <kluker@xxxxxxxxxxxxxxxxx>]

If a viewer had lenses with differing focal length, they would not 
both focus on the slide at the same time, so one eye would see a 
focused image, (IF the camera produced an in-focus image!), the other 
would not, you choose which.  But if a camera has fixed focus lenses, 
with one focused relatively near and one relatively far from the 
camera, the slides taken may well be acceptable.  If the far-focus 
lens created an image that was sharp from infinity to, say, thirty 
feet, and the near-focus lens created an image that was sharp from , 
say, fifty feet to three feet, then the mounted slide would present 
to the MIND a picture that had good focus AND bad focus, all over the 
picture.  The mind could then sort it out and perceive selectively 
the focused parts, letting the un-focused parts contribute mainly the 
stereo information.  I believe this is the reasoning behind the 
choice by the camera manufacturer to skip the expense of a focusing 
mechanism while still permitting near and distant shots at reasonably 
fast shutter speeds (without extremely small aperture.)  It's a 
compromise, and not as satisfying as a well-focused image throughout 
for both eyes, but some may believe it is worth the cost savings. 

Ken Luker

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Kenneth Luker
Marriott Library Systems and Technical Services
KLUKER@xxxxxxxxxxxxxxxx


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