T3D Re: Single Lens Stereoscope?

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

Apologies for my earlier post where I hit the send button to soon by mistake.
John Bercovitz replied to my post


>I'm not sure what it is that you don't understand.  My apologies for
>being so slow.  I'll try to explain anyway.  Not knowing what I'm
>talking about should not be an impediment to free discourse.  8-)
>
>The stereocard is on the ground and upside down to you.  You put a
>long lens between you and it.  The lens makes real images nearer
>your eyes than the object or lens.  These images are inverted.  The
>lens also acts as a pinhole causing the left image on the ground to
>be directed to your right eye.  Since the image on the ground is
>inverted, its right image is on your left.  The pinhole effect,
>then, corrects this.
>
>Was it a clean miss?  8-)

Thanks for that explanation I think I see it now, it was actualy easier for
me to understand with the virtual image version. This produces a single
large stereo image and when I shut one eye then the other it is clear that
this is made up of   the opposite halves to each eye as the aperture of the
lens blocks the image on the same side but allows the opposite side to be
seen. This explains why it is pseudoscopic as well. This is rather similar
to a device which is just an aperture with no lens for training people to
cross view. With the real image version both images of the pair are visible
with just one eye but are displaced to the opposite sides of the lens .With
both eyes open the inside images of each left and right overlap in the
centre to give the stereo image. Much like freeviewing or with a long focus
stereoscope without a septum.
  John Bercovitz seeems to familiar with this phenomena but how well known
is it did the Victorians know about it ? is this the reason for the large
lens on a stereographoscope?. The usual explanation is that it is for
viewing large non stereo views with perhaps some depth sensation if the
view is coloured through chromostereopsis. Why did Duboscque and Maxwell
think they needed two intermediary lenses? more recently Jeremy Hinton who
is a member of these groups
wrote an article in the UK stereoscopic society bulletin about how he came
to the same idea as Maxwell independantly after reading about optics. But
he still used a conventional stereoscope first before his Fresnel lens or
mirror.
                                                  Peter Homer




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End of TECH-3D Digest 305
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