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Date: Fri, 22 Jul 94 10:32:31 PDT
From: [e-mail] (Bill Mills)
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Subject: Re:  Magnifying glass
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Brian Dady wrote to the list:

>Refraction seems to work quite well, except in one case.  I've been
>trying to make a magnifying glass with some text partially beneath
>it and partially not.  The idea is to see the effect of the magnifier
>lense.  I modelled the convex lense object by squishing a sphere, so
>it is not exactly like a true lense.  I've given it the characteristics
>of glass and tried rendering with different spacing between the lense
>and the text plane, but to no avail.  It *appears* to be magnifying
>near the edges of the lense due to the distortion, but maybe not.
>Away from the edges it looks perfectly normal (unmagnified), except
>that the text is washed out.

I've done exactly the same thing, quite successfully.  I squashed a
sphere, and gave it a bit of specularity, and an optical density of a
heavy glass (forgot te exact amount), and turned double sided polygons
on.  Someone mentioned that the exit planes should have the optical
density of air (1?) but that didn't seem to work well for me.  The key
factor in refraction is the difference between optical densities.

Allen, does Lightwave count the value we put in as how much to refract,
or does it calculate the differences based on the optical density of the
object, and an assumed optical density (1?) for the 'empty space'.  If
this is the case, can we change the environmental density to replicate
shooting underwater more accurately (as if accuracy were more important
than simple looking good)?

>Does lightwave deal with refraction only on a surface basis, so that
>the actual thickness of an object doesn't matter, only being affected
>by the surface normals?

The thickness does not matter in refraction, just the angles and optical
densities (hence the fresnel lens works while being nearly flat).  I
suspect that your lens is too flat, my first few attempts were.  The
center surfaces should not be nearly parallel, or they won't have much
effect on the light.  It also took a few sttempts to get the lens placed
properly in comparison to the camera and subject.  If I ever end up with
more rendering time/horsepower than I need, I want to do a short anim of
lenses spinning into place, being surrounded by a brass tube to form a
Galilean telescope, and then focus through that to a distant bitmap of
the moon.

Be seeing you....
-Bill Mills

[e-mail]
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