P3D Re: red button's aberrations

[Larry Berlin <lberlin@xxxxxxxxx>]

Date: Tue, 06 Jan 1998 
>From: Peter Abrahams writes:
>........
>Larry said he could
>>sense the
>>distortion created by the optics themselves. The entire view in a RED button
>>is presented as if it's painted on the inside of a bowl. 
>
>I believe this was an imprecise use of distortion, which should not mean
>'any change in the image', but means a difference in magnification between
>the center of the image and the edge of the image.  This causes a
>pincushion (increased magnification at edge) or barrel (decreased mag)
>appearance in lines that are near the edges.  This aberration in a red
>button is very slight.

****  I consider what I observed to be a field curvature in 3 dimensions,
and any field curvature would be a distortion relative to the flat field of
an ideal situation. Whether it's caused by differences of magnification,
lens mismatch, or a defect in the material, it's still a curvature of the
field, which is still an optical distortion... I couldn't think of the term
*field curvature* at the point of writing, so described it in a literal
sense to get the point across. Actually had I thought of the right term when
seeing the effect, I might have remembered it when writing about it... :-)

>
>The appearance of an image as if projected into the inside of a bowl is not
>something I would dismiss, though I've not seen it.  Stereo does have a way
>of rendering some image qualities as plastic, sculptural, or tactile.
>Aberrations are there in the image, mostly unnoticed, but the idea that
>stereo can render them more plastic is very interesting.  

*****  Now I wonder about your terms... plastic could mean looking like
plastic, shiny, smooth surfaced, popped out of a mold, or it could mean able
to be flexed or bent without breaking...  One of the great properties of
stereo is that a small amount of parallax has significant results. Changing
parallax factors on a computer image provides a sense of being able to
sculpt the image like plastic. Viewing a known image on a monitor screen
that has distortions can be startling when some distant feature seems out of
place relative to other aspects. It remains strange until the screen
distortion is understood and ignored, causing the sense of the image to sort
of correct itself.

I've always considered stereo images to be tactile, with my eyes
substituting for a means of physical touch.

>.................
> This discussion reminded me of a letter to Sky & Telescope, May 1995, p8,
>on the illusion of stereo when viewing the stars with binocular viewers
>(excerpts:) 
>===============
>"....the intervening optics are responsible for producing the stereoscopic
>effect.....the viewer really does see a three-dimensional image in most
>binocular telescopes.  However, the stereoscopic cues are caused by
>aberrations in the optics, particularly those in the eyepiece.....residual
>field curvature and astigmatism, which present a curved image to each eye.
>When the eyes are not perfectly centered over the exit pupils, the curved
>images are seen from slightly different points of perspective, resulting in
>a 'three-dimensional image'.  The effect is most pronounced in the least
>complex eyepieces, such as Kellners and Ploessls." --R.A. Buchroeder
>===============

****  Interesting story. Now I want to try a Binocular Telescope!

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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