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Thread: Cheap planetarium/hemisphere projection lens

  1. #1
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    Default Cheap planetarium/hemisphere projection lens

    Hi PhotonLexicon,

    I am looking for a planetarium/hemisphere/projection/wide angle/fish-eye type lens to increase the scan angle of a projector, ideally to 180 degrees for an aerial beam show. For this simple application, most aberrations are no concern so many different types of lenses may be suitable.

    Pangolin have a product called "Discoscan" which sounds ideal, but it is very expensive (http://www.pangolin.com/images/widea...scanAngles.gif). Another idea I had is to use the lenses out of a rear projection TV (http://www.dgibbons.members.sonic.net/essay7image.JPG), but I suppose the scan angle would still be smaller than with the Pangolin lens.

    Any other ideas for cheap sources of such lenses?

    Kind regards,

    weartronics

  2. #2
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    they have halve sphere mirrors with 50cm diameter here in shopping malls. They are mounted on the ceiling as 'security' system.
    I also believe they are first surface mirrors, but I doubt that they have good reflectivity. Anyway, you wanted cheap...

  3. #3
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    Cool

    Weartronics;

    The reason the lens from Pangolin is so expensive is that 1) they pay a license fee to AVI for the technology behind the lens, and 2) the lens itself is massive.

    You might be able to find a cheap alternative, but you're going to run afoul of AVI's patent if you do. Not sure how aggressive they are about defending their intellectual property, but they could go after you if they wanted... Your call if you want to take the risk.

    I've actually held the Pangolin Discoscan lens in my hand. It's very impressive. While I know it's expensive, trust me when I say that it's the last one you'll ever need to buy.

    Adam

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    Hi Buffo,

    Thanks for the info about Discoscan and raising the AVI issue. My main concern is that the Pangolin web site suggests that the Discoscan coating may not be compatible with Q-switched Laserscope , and I wouldn't consider buying it unless they could guarantee performance and survivability in this application ! This is why I'm looking for a throwaway lens, where I don't care if the coating is damaged.

    I haven't found any suitable alternative, so I plan to start with the rear projection TV lens. Fortunately, there is no licensing fee to use a TV lens in this application , and amongst other differentiating features, my design wouldn't use any fiber optic cable so it wouldn't infringe the AVI patent . As an aside, this would be a one-off design for non-commercial use (not that this affects any licensing or patent issues of course).

    Hi highvolt,

    The mirror dome is a great idea, but I forgot to specify, my application is outdoor aerial beam show, so I need the 180 degrees up in the air rather than down on the ground, this was probably not immediately obvious . Though nobody is stopping me from putting the mirror dome on the floor with the projector on a tripod above .

    weartronics

  5. #5
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    Recent experiences with 30 watts of KTP suggest most coatings will hold up. start with a minolta camera lens, and see if the coatings take it. I believe minolta made AVIs custom lens, but they will not sell it to you directly. You can bet however that the coatings are similar and done in the same lab.

    There is far more to that lens then just a "wide angle" camera lens. I can reference you the patents for flight simulation lenses if you wish to see the differences, and I have a email some place from a guy who designs them, if you wish to talk to him, but in 6 years of trying I've never found anything that was commercial, cheap, and had infinate focus like you need. I have found some things that would work on a dome at one radius, but never with a collimated beam or truely circular spot. pay the bucks for discoscan.

    Steve Roberts

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    Quote Originally Posted by weartronics View Post
    My main concern is that the Pangolin web site suggests that the Discoscan coating may not be compatible with Q-switched Laserscope , and I wouldn't consider buying it unless they could guarantee performance and survivability in this application ! This is why I'm looking for a throwaway lens, where I don't care if the coating is damaged.
    Hmmm. I haven't looked at that web page in a while, but as far as I know, there is no known power limitation handling capability of that lens. As far as I know, some of our customers indeed use it for high power and pulsed YAG applicaitons.

    To me the bigger problem might be the entrance aperture of that lens. The entrance aperture is around 1/2 inch. That might be too small to get a scanned beam from a YAG into it. We do have a larger lens design, but it has to be used with a separate collimator in most circumstances.

    By the way, what the heck do you need 180-degree scanning with a YAG for anyway?


    Quote Originally Posted by weartronics View Post
    I haven't found any suitable alternative, so I plan to start with the rear projection TV lens. Fortunately, there is no licensing fee to use a TV lens in this application , and amongst other differentiating features, my design wouldn't use any fiber optic cable so it wouldn't infringe the AVI patent .
    I wouldn't be so sure about that. The picture might show a fiber, but the fiber is actually not a part of the patent. In reality, any lens you put in front of the projector that is used for either a full-dome scanning, or "balloon" application will infringe AVI's patent, and they are very agressive about pursuing the IP of this (just ask one competitor that cropped up, and is now out of business...).

    Best regards,

    William Benner

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    Quote Originally Posted by Pangolin View Post
    I wouldn't be so sure about that. The picture might show a fiber, but the fiber is actually not a part of the patent. In reality, any lens you put in front of the projector that is used for either a full-dome scanning, or "balloon" application will infringe AVI's patent, and they are very agressive about pursuing the IP of this (just ask one competitor that cropped up, and is now out of business...).
    Hey I just applied for patent for full scanning on not even and poorly made mirror. Also any lens put infront or behind galvos or any projection element. I'm plaining to file a lawsuit against Edmouns and Thor labs.
    I hired an Italian guy to do my wires. Now they look like spaghetti!

  8. #8
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    Hi Bill,

    Thanks for your comments. I have searched, and as you're probably aware, there is no serious alternative to the Discoscan lens for this application. Your comments about power handling are reassuring, so I would like to consider the Discoscan lens.

    My application is for an aerial beam show (with the lens upside-down relative to a typical indoor installation), hence the high power requirement. Can you send me any detailed specification for the Discoscan lens? I would like to know what entrance aperture and acceptance angle are necessary to achieve 180 degree scanning, and what effect the lens has on the beam divergence.

    -----

    However, I think you are mistaken with regard to the scope of the AVI patent. I am seeing a lot of fear-mongering on this issue (intentional or otherwise), so I want to present a clear defense.

    Quote Originally Posted by Pangolin View Post
    I wouldn't be so sure about that. The picture might show a fiber, but the fiber is actually not a part of the patent. In reality, any lens you put in front of the projector that is used for either a full-dome scanning, or "balloon" application will infringe AVI's patent, and they are very agressive about pursuing the IP of this (just ask one competitor that cropped up, and is now out of business...).
    As an inventor and author of numerous patents yourself, you must be aware that the description of the invention (including figures) has no bearing on what is claimed. To my knowledge, AVI only have one patent (US 6,698,900 with possible derivatives in other world regions), which has only one main claim:

    Quote Originally Posted by AVI
    1. A mobile, reverse projection system comprises an electronic control unit (ECU) and a projection head mounted on a balloon, wherein said projection head and said ECU are joined by an umbilical cord and said umbilical cord comprises at least one power transfer cable to supply power to a plurality of deflectors in said projection head and at least one fiber optic cable to transfer light from a light source in said ECU to said projection head for projection within said balloon.
    It is clear that a projection system which does not incorporate any fiber optic cable would not infringe this claim (or any of the subsequent, narrower claims) .

    Kind regards,

    weartronics
    Last edited by weartronics; 06-12-2008 at 20:12.

  9. #9
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    How about an overhead projector lens?
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    That is a fresnel lens. It's plastic and I can't imagine what strange things it would do to a fine point laser beam. I should try it!

    But only in the privacy of my own home!

    James.

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