T3D Re: stereo math

[john bercovitz <bercov@xxxxxxxxxxx>]

Curmudgeon Abram Klooswyk writes:

> When you use the same mounts, projector, screen, viewers for macro as
> well as for other slides, making shows mixing slides and so on, it is
> obviously erroneous to use a doubled on film deviation when shooting 1:1
> macro's, in which the working focal length is doubled.

Could you say that one more time with a little more explanation?  I think 
I might get what you're saying if I study it a little longer but what the 
heck, if you say it in more expanded form I'll be sure.

The way I see things (and the way the maofd spreadsheet treats the problem), 
if you shoot with a lens which is twice as long (and this could be because of 
a 1:1 shot), then you need to occupy a perspective point which is twice as 
far from the image.  Is that what you are saying too?  That's why I mentioned
that one has to take into account the increase in the distance from lens
to film when doing macros.

Also, I would agree it is not always comfortable to mix single and double
depth slides, regardless of whether they are macro or whatever.  Were you
also saying that?

Thanks,
Curmudgeon John B


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