[MF3D.FORUM:798] Re: I need a MF 3D Dr.

[Paul Talbot <ptww@xxxxxxxxx>]

"Dr. George A. Themelis" quoted and wrote:

> >Drawing on an example I
> >was given, let's say the closest object in a scene is a coin
> >standing on edge, thin edge toward the camera.  Say the physical
> >depth in the scene is not very great, and the scene is fairly
> >close.  The MAOFD formula may yield a stereo base that is
> >significantly larger than 1/30 the distance to the near object.
> >It is possible that the left camera will see the "heads" side of
> >the coin, while the right camera sees the "tails" side.  When
> >you go to view the two images in 3D, there will be problems,
> >even though the MAOFD has not been exceeded!
> 
> Two comments on this:  The coin that stands on its thin
> edge toward the camera is not a particularly good example
> of a subject with limitted depth, especially if photographed
> in a close up. Standing on its face would be a better example
> but then it does not have the problem you described.

To clarify the original example, the coin on its edge is
simply the *nearest object* in the photo, not the entire
subject matter of the photo.  We don't need to limit the
depth THAT much for the problem to arise.

> The other
> comment is that when our eyes look at the coin on its side,
> we do not seem to be bothered by the fact that the left eye
> sees quite a bit of the left side and the right eye
> sees quite a bit of the right side.

Darn, why can't I think of the simple things like comparing
the photo example to the real world!?

On reading your post, I tried it.  And it DOES bother my
eyes.  I either see a double coin, or my perception flips
back and forth between seeing the heads and tails.  I
cannot find a location to place the coin close to my
eyes that I can see both sides and not be bothered by
it.  (If held at a distance, we are not really seeing
the sides of the coin, just a flat surface.  At a
distance from our eyes, our "stereo base" is not wide
enough to look *at* the sides of the coin, as a pair
of widely spaced cameras would.)

> >Extending the example to more likely real situations, it is
> >easy to see that if the base is so large as to see different
> >sides of a near object, fusing the two chips into a pleasing
> >3D image could be quite difficult or impossible.
> 
> I would think that the stereo base would have too be way
> too large for this to be a problem in a practical situation

That's a good point, but what is "way too large?"  In some
cases the MAOFD approach recommends a base that is several
times larger than 1/30.  I also think that when Bill first
started studying the stereo base, he told me his spreadsheet
comparing results sometimes had even an order of magnitude
difference.  So there is a lot of room for "way too large"
to occur.

> and you will first ran into other problems (like insufficient
> overlap between R and L).

Yes, but doesn't that depend on the film format?  When working
with 6x7 images to be mounted in 50x50 mounts (or shooting
full frame 35mm and mounting to 5P), there is a lot of film
to the sides to absorb that non-overlap area.

> From DrDave's posting it seems that mounting was the problem
> here.

Way to go David!!  :-)

> Our club's newsletter had a nice write up on the stereo
> window.  I will send Bill a copy.  I think it will clarify
> a few things about mounting and the stereo window.  Also,
> in NSA DrDave will demonstrate mounting of stereo slides.
> Perhaps DrDave or Paul can include MF mounting as an example?

I'm incapable of MF mounting.  In fact I can't wait to see
David's techniques (MF AND 35mm).  How many times is DrDave
giving the workshop?  I want to see it every time and study
his every move!!  Anyone bringing a video camera?  I want
a copy of the tape to bring home with me!

Paul Talbot