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 Originally Posted by steven_e007  But how on earth do you encode two images on one sheet of paper with different polarisation? That's hardly possible.
Originally Posted by steven_e007 I'm beginning to think you might need to make a sandwich of BW slides with polaroid filters... but surely the top filter would block all the light from the image/filter underneath? No, don't make a sandwich of slides. What you need to do is use two slide projectors and somehow put a polarizer in front of their lenses. Make sure the filters are 90° turned with respect to each other around the filter axis. With a setup like this you basically project one slide with some polarization, and the other slide with the orthogonal polarization.
If you now hold a simple polarizer filter in front of your eyes, you can see the projected image of either one or the other slide. Now make glasses where each eye sees only one polarization and you're set.
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Originally Posted by Rudeofus That's hardly possible. It must be possible, because I've seen it!
There is a type of test chart used in opticians which uses polaroid spectacles - and for some reason it is usually an image of a house fly... I can't workout how they do it, though...
No, don't make a sandwich of slides. What you need to do is use two slide projectors and somehow put a polarizer in front of their lenses. Make sure the filters are 90° turned with respect to each other around the filter axis. With a setup like this you basically project one slide with some polarization, and the other slide with the orthogonal polarization.
If you now hold a simple polarizer filter in front of your eyes, you can see the projected image of either one or the other slide. Now make glasses where each eye sees only one polarization and you're set.
Yep... I can see where you are coming from. That is an interesting idea. I bet it would be pretty tricking to align the two projectors exactly, though...?
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Originally Posted by steven_e007 It must be possible, because I've seen it!
There is a type of test chart used in opticians which uses polaroid spectacles - and for some reason it is usually an image of a house fly... I can't workout how they do it, though... Interesting, never seen this. Is this a printed test chart or some backlit slides?
Originally Posted by steven_e007 Yep... I can see where you are coming from. That is an interesting idea. I bet it would be pretty tricking to align the two projectors exactly, though...? It should be pretty easy since both projectors can be placed close to each other and you can use some edge in the picture to help you with the alignment. As long as you don't wear the polarizer goggles, you just see two images projected on top of each other.
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Originally Posted by Rudeofus Interesting, never seen this. Is this a printed test chart or some backlit slides?
. Hi....
No, nothing is backlit - it is just a flat sheet. I'm beginning to think it is maybe some clever sandwich of layers and filters or something - but I can't see how it is done.
Here is a link to one:
http://www.eyesfirst.eu/epages/61989...jectID=5973646
The test I used wasn't a titmus fly test - it was a different make, but still a fly (seems flies are traditional for stereo testing!). The titmus is mounted in a folder, so could be quite a thick sandwich of something, but the test sheet I saw was just like a laminated photograph - really not so thick.
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Wow, learn something new every day ... apparently these test sheets use a vectograph for creating this effect. Not sure how to make such a thing at home. Note, that you can not replicate this with regular slides and polarizer gel!
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Well done, how did you find that?!
I searched for hours and kept getting shunted into red / green anaglyphs every time.
I loved this bit:
Joseph Mahler (cousin of famed composer/conductor Gustav Mahler) is the inventor of the Vectograph.
Amazing!
Looks like you need special Polaroid Vectograph film... which I suspect is probably not available any more :-)
.... mind you, they still make Titmus fly test sheets. Hmmm... more investigation needed, I think.
I've found links to StereoJets, now. This appears to be a modern updated version of the Vectograph but made with DIGITAL technology. (washes out mouth with soap...)
http://stereojetinc.com/html/applications.html
There's some hints about the original technique here:
http://www.3dculture.com/occ/Panoram_StereoJet.htm
This guy has some lenticulars and StereoJets taken from old BW stereo images in his gallery:
http://stereojets.com/
Obviously you'd need the originals to see them in 3D - but intriguing that he has got from old Black and White pics to polaroid stereograms, somehow. No doubt using digital again, taking us off topic...
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I'm well away, now...
Here's a link to the supplier of vectographic film.
http://corporateportal.ppg.com/NR/rd...aphNewsRel.pdf
Right at the bottom of the article is the very test chart that I have seen and can see perfectly in 3D.
No idea who much this vectographic film is - or if it is the sort of thing you could use at home, they don't list it on their website.
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Steven...just sent you a PM regarding optomotrists.
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