[photo-3d] Re: Medium Format viewer

[Alan Lewis <3-d@xxxxxxxx>]

> >Don, if you are listening, what was the lens focal
> >length of that viewer?  65mm?
>  
> Wow! That should give a really BIG image... does that add a
> lot of distortion?
> Does a lens with a different focal lenght than the "normal"
> changes anything in the perceived depth of the stereo
> image???

Choosing the viewer lens to use is a tradeoff.  I have found that it is
almost impossible to find one lens that will accomplish everything one
wishes for.

A medium format viewer could use a lens of approx. 60 to 65mm and still
cover the full image, but I have not yet found a lens that will do this
distortion free.  
I think Don's viewer lens is even shorter than this.  What happens as
you go to a shorter f.l. viewer lens (beside the perspective change
George mentioned) is that you go towards the full circle type of image,
without the mount window being in the image.  Distortions can increase
if you use a large diameter lens that is necessary for medium format
viewers. But the distortions may not be objectionable because you feel
so immersed in the image and you no longer have a well defined window in
the mount to judge the type of distortion you are getting.  It probably
just amounts to a sharpness judgement from image edge to image edge.

My personal preferences are that the medium format image (or any stereo
image) must be sharp from image edge to edge (corner to corner).  That
is my first criteria.  Second is the image coverage of the lens.  The
bigger in dia. the better. Third is the pincushion or barrel distortion
judgement (it's always a judgement). Fourth is the focal length.  I try
to stay with an ortho lens arrangement for my camera/viewer (75-80mm
f.l.).  This is as much for practical reasons as for perspective
reasons.  Practically speaking I have found that any lens less than 75mm
suffers too much from some of the conditions that I have mentioned
above.

But I continue to try any and all lens spec's in my medium format viewer
that I can get my hands on.  The experimenting is enjoyably, and so
educational.  Nothing beats actually trying something rather than
following what others' say is right or wrong.

-- 
Alan Lewis  
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http://members.home.net/3-d
Serious viewers for Serious viewer's
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