T3D Re: Phanto-cam Lens system

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Larry,

> >Thought #1
> >
> >Lenses for off axis viewing are usually called "pantoscopic". They are
> >expensive but commercially available. They avoid the keystoning that
> >occurs when you photograph a tall building from street level. They can
> >sometimes be decentered different amounts to accomodate the preferred
> >viewing angle.
> 
> *****  These are great comments!  Interesting name, quite close to
> *Phantoscopic*! Do you know where to get more information on this type of
> commercial lens? Catalog or URL?

It seems to me that I once had a brief catalog of Canon lenses that
included a Pantoscopic lens. Maybe a web search would turn up something.
I'll see what I can find in my catalogs and textbooks.

> >Thought #3

<big snip>

> 
> ****  This last item is very interesting. I wonder if one could model an
> afocal lens within a 3D program and use it for phanto-imaging? Is there
> somewhere to find an approximate cross section for an afocal lens/system?

You will have to indulge me here. I am an optical engineer but fairly
new to photography and stereo. I am not sure what you mean by an
approximate cross section. Do you mean the curves and glass types to do
a ray trace? Also, I don't know what a phantagram is? I was just reading
the comments about off-axis imaging and jumped in.

A few years ago off-axis imaging was my bread and butter. I designed
systems for non contact distance measurement using a laser as a source
and a CCD line array as a detector. The imaging optical axis was
typically 30 degrees off of the laser axis. The laser line was imaged
onto the CCD array. The array needed to be tilted in order for any point
along the laser to be in focus. We usually used a single or double
imaging lens because we did not care about the non-constant
magnification.

Since the laser line is the object, the object tilt is about 60 degrees. 

But an afocal imaging system would have given us a simpler system from a
programming standpoint. Each CCD pixel would represent a constant
distance along the laser. Whereas with a single lens the CCD pixel for
the farthest laser point collects from a longer length of laser than the
CCD pixel for the nearest laser point. So accuracy is good when the
target is near and bad when the target is far away. A lot like human
vision n'est pas.

Tom Hubin
thubin@xxxxxxxxx


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