Re: [photo-3d] Re: Better Viewers

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

----- Original Message -----
From: "Dylan the Hippy Wabbit" <dylan.wabbit@xxxxxxxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Saturday, March 31, 2001 4:57 AM
Subject: [photo-3d] Re: Better Viewers


> Hi All,
>
> Mike Galazin asked:
>
> >If one can use two achromats together to achieve half the focal length of
> a
> >single one, then what would you get for focal length with three achromats
> >together?

Anytime you add several elements together, you change the overall
configuration of the performance of an optical system in more ways than just
magnification ratios, often introducing aberrations and distortions.  These
have to be corrected with - you guessed it - even more elements.  To keep
from getting impractical, such designs require careful calculation.  Today,
ray tracing programs such as Oslo make this practical for even relatively
small production applications, and the price of a qualified optical design
engineer is not that large a proportion of a manufacturing budget.

If you are just thinking of making something for yourself, you are usually
better off to try to make use of "off-the-shelf" components.  Already
assembled lens configurations, often available surplus, can be a much lower
cost approach.

Also, consider that with added elements, the back focal distance (to the
eyes) in conventional simple designs usually decreases (more distance from
the nodal points) unless this is also compensated by such things as retro
focus designs.  This can result in less eye relief, and require even larger
diameter elements to avoid vignetting.

JR


 

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