re: the elements of lenses in stereo Viewers

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Lincoln Kamm writes

>I was just noticing last night that some slides I looked at in a stereo
>viewer (that I am pretty sure has single element lenses) seemed to have some
>color shift or a blur of color that moved when I looked through at
>different angles of the lenses.  Is this because it is single element, or
>could it be something else?  Is there anything I can do to fix this problem?

Yes your quite right that it is due to it being a single element. Also as you
have observed, this is more pronounced off center. That is one of the reasons
I had mentioned in another post, that it is better to have provisions for 
interocular adjustments especially on single lenses.

This is usually more prevalent on higher magnification viewers and is due
to the separation of the light into its component colors or dispersion. Of
course a prism behaves in this manner and is basically what also happens at
the edges of the lenses. To decrease this dispersion or chromatic aberation,
better viewers use achromatic (refracting light without dispersing into its
constituent colors) lenses. The dispersion qualities of a lens depends on 
the refractive properties of the lens material. Different materials will
bend the light rays more or less depending on what it is made of. Thus if
two different materials with different refractive properties are used in
an achromatic lens then the refraction of the light rays can be made to
cancel out or greatly reduced. 

So basically yes something can be done to fix this problem. As I a pretty
sure Dr.T will agree with me, is to get a better quality multi-lens viewer
with achromatic lenses. BTW this dispersion is put to good use in the 
ChromatDepth 3D glasses.

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 | 3D / \ 3D |   |3D  / \3D  |
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