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DIY anamorphic lens
DIY anamorphic lens
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Old 19th July 2002, 08:48 PM   #1
hoxford is offline hoxford
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Default DIY anamorphic lens

I thought I'd start an anamorphic lens topic for any AVS Forum members browsing around or anyone else interested in the topic.

First off, here's a link to Tor Arne's site describing in great detail his construction of an anamorphic lens (several actually):

http://home.c2i.net/ahustvedt/arnemorph/

For you German speakers, here's a link to the site that did the original R&D on the lens:
http://ww2.bepo.com/jochen/anamorph/

I think there's a link there to the German discussion forum where the original ideas were hashed out. Sorry, I don' t have it handy and don't speak German well enough to find it.

There's also some interesting info on prisms and anamorphic lenses here:

http://appft1.uspto.gov/netacgi/nph-...l&r=0&f=S&l=50

We've been moderated out of existence on the AVS Forums so I'm hoping some of the other 'rejects' from there will come over here and we can get a good discussion going.
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Old 19th July 2002, 11:34 PM   #2
tahustvedt is offline tahustvedt
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Hi, I will check back to this forum daily and hope there we get a lot of replies from AVSforum members.


Some notes.

-The lens works upside-down too, but this gives more lens-shift and more uneven focus.

-I will try to compensate for the barrel distortion in only one direction instead of both like I have with my previous models. The compensation gives some focus-drift towards the corners that I want to avoid. Compensating in one direction only will give a better optical surface as it's possible to bend more accurately than with my previous methods. The left and right edges will have curving to them just as a non-corrected lens, but I don't see that as a problem. The problem area with non-corected lenses are the top and bottom edges IMO.

-I will try to make the corrective surface on the oilprism instead of the waterprism. I was worried that the lexan wouldn't be able to withstand the turpentine as it is a strong solvent, but after bathing a piece of lexan in red spirit for ten hours I'm confident it will work (I didn't have any turpentine with me at work to test with).

-Pure turpentine still works great as a substitute for turpentine oil. They are basically the same thing, turpentine contains 75%-100% turpentine oil addording to the data-sheet.

-The water does seem to attack the epoxy-glue somewhat and silicone sealant works better for the water. However silicone sealant isn't overpaintable, which is a drawback. The paint will form drops on the surface of the silicone after a few seconds. My final version will probably have silicone instead of epoxy for the waterprism. I'm not sure how the silicone sealant stands up against turpentine.

-I want to try making a horisontal expansion lens as well. It shouldn't be any more difficult, all I have to do is design it backwards and rotated 90

-I wish I had a projector which didn't have such an extreme short-throw lens. It does however make my design very versatile and if it works with my projector then all other projectors with longer throw should be able to use a similar lens.

-If it's possible I might try to make a 2.35:1/1.78:1 adjustable lens, but I'm worried about the amount of chromatic aberrations and barrel distortions becoming too bad. If I compensate the geometry in only the vertical direction the problem will be reduced, however.


I hope I will have the time to experiment more in the future, I might have to send my projector in for repair (again) and my left B&W CDM7-NT speaker has started to make a fretting noise from the bass-driver so I will have to send that in as well. I can't possibly watch movies without the speaker or projector. I will be dead for the period they are away.


Tor Arne
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Old 20th July 2002, 03:07 AM   #3
woneill is offline woneill  United States
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Hi Guys,

Interesting ideas!

I have previously been exploring the topic of anamorphic lenses myself, but in my case I was looking into using a pair of cylindrical lenses (one each PCV & PCX - both with the same focal length) to expand the beam horizontally, and possibly also using another pair to compress the beam vertically at the same time. (This would reduce any distortion in a single axis.)

Unfortunately, the lenses I have been able to get so far are very poor quality, and the results were unimpressive.

Your use of liquids to form the prism body is cool. Have you considered exploring those transparent epoxy packs available for use in embedding things within a plastic block? You might be able to get away with only needing one liquid device. (I'm thinking about leaks etc.)

Bill.
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Old 20th July 2002, 09:58 AM   #4
tahustvedt is offline tahustvedt
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Is it somekind of molding material? The material would have to have the right refraction index, somewhere close to turneptine. If the refraction index is different the angles need to be changed.

Interesting idea about compressing and expansion working together.


Check out this patent with lots of ideas but unfortunately no calculations:

http://appft1.uspto.gov/netacgi/nph-...DN/20020063975

It has many auggestions for how to make a lens and how to correct different artifacts.


Tor Arne
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Old 20th July 2002, 03:12 PM   #5
tahustvedt is offline tahustvedt
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I don't think this has been mentioned before.

The right way to mount the lens is as follows. If the projector is ceiling mounted the peak of the waterprism should point downwards and the peak of the oilprism should point upwards. Like I said it will work the other way too, I guess you have to try for yourself which way is best.


Tor Arne
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Old 20th July 2002, 04:29 PM   #6
woneill is offline woneill  United States
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Hi,

Of course I can't find a link when I want one, but to give you some ideas of the properties, and see if the stuff is in the ballpark, try these links:

http://www.loctite.com/pdf/doming.pdf
http://www.loctite.com/pdf/ComparPro...learEncaps.pdf

The stuff I was actually looking at is generally available from Home Depot in the US. It is clear, transparent, and designed for encapsulating things into table-tops, trays etc.

I was thinking of using it to make large PCX field lenses for the LCD panels instead of fresnels, but when used correctly, the fresnels weren't too bad.

You put whatever you wish to encapsulate on the surface, pour over the epoxy as if it were water, and let it set. (Of course, you must build a waterproof frame around the edges...)

I have seen this used with thicknesses up to an inch.

Bill.
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Old 20th July 2002, 04:47 PM   #7
woneill is offline woneill  United States
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I tried the Patent link - it will definitely take me some time to digest...

Bill.
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Old 20th July 2002, 05:21 PM   #8
tahustvedt is offline tahustvedt
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It would be possible to make a mould from glass. The problem would be getting the prism out of the mould, even if the mould was expendable.


My apporach to the lenses is a bit silly as I'm trying to make it small. By making it a bit larger it will work better but it will be ugly. I just mention it so you guys know why I'm making so many different versions.


Tor Arne
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Old 21st July 2002, 05:16 PM   #9
hoxford is offline hoxford
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For the loctite materials, the problem is that the current DIY lens design is based on the the optical properties of turpentine oil and water. It seems that the refraction and dispersion properties of both materials are important to get the desired bending of the light while reducing chromatic abberation. This is what I've read, anyway.

However, it seems that "commercial lenses" of this sort (liquid filled prisms) just some sort of mineral oil. I'm not sure how the correction for chromatic abberation is handled there.

There's a patent on handling chromatic abberation in prism based lens systems...

http://patft.uspto.gov/netacgi/nph-P...S=PN/4,704,008

...but it's over my head at the moment.
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Old 21st July 2002, 05:22 PM   #10
tahustvedt is offline tahustvedt
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It's way over my head too. I think I'll stick to what works for now.


Tor Arne
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