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lenses

Discussion in 'Lighting and Electrics' started by dj_illusions, Oct 3, 2004.

  1. dj_illusions

    dj_illusions Active Member

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    Location:
    Melbourne, Australia
    hi all..

    a local theatre group, out of pure stupidity whent and bought three second hand lamps, all three are in terible condition, no yoke or leads and riddled with rust, however they seem to think its the best thing since sliced bread.

    two of the fixtures actually done have any lenses in them at all. the fixtures are of no particular brand or make, and have no serial number. however they seem to be based off a harmony or minuet fixture, and have a pc lense (from looking at the one with a lense) the only markings is a "moonshadow" written on the side.

    wondering if anyone could help source some lenses or if it is just better to cut their loseses and try again next time?

    jeremy
     
  2. ship

    ship Senior Team Emeritus Premium Member

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    Can you post a photo of them?
    I inherited a Bantam Superspot without lens, wire, yoke or gel frame bracket at one point. Had to make both lens clips and gel frame bracket for it. That and a yoke also had to be made to conform around the body. Takes a 4.5" PC lens. Such lenses are standardized parts and if a plano convex, making it into a Fresnel is also very easy to do as a viable option which could be more useful for the stage given they are PC. Did this with some old 400w Kliegl PC’s to some effect at some point. The reflector is similar and for the most part most PC’s I have worked on from the Altman 101 to some from Major for the most part take the same parts as a Fresnel. You for instance will probably be able to use a Fresnel’s reflector and slide assembly in them because the fixture about works the same.

    In any case, the lenses be them 6" or 4.5" should be easy enough to come by from most theater supplies as it’s standard parts for old gear. If I remember right a 4.5x6.5 lens is what I ended up installing in my above spot. Probably a wider beam angle lens than origionally was made for the fixture but with this brand there was lots of options available from slide projector to Fresnel. Given it’s a 4.5" lens, the Altman 4.5x6.5 Leko lens should work fine. Otherwise I might go with something like a 6x9 lens if a 6" pc. In any case, the lenses are about the same and generally available thru theater supply companies.
    Otherwise I have some links to some lens companies that should be able to help you out.

    You will need to know this to match the lens exactly otherwise:
    Radius and Focal Length: Lenses are about .52 times their focal length by radius of curvature of the lens. For ellipsoidal lenses. In other words, figure out what the radius is and it’s .52 of that. I used to have a better formula where you just measured how high the lens sat and punched it into the formula but I expect with the given info above, such a formula can be created.

    The yoke is easy enough to bend out of some steel bar if the shape does not conform roughly to that of a similar shaped instrument. The missing wiring is probably better off gone as something you no doubt will have needed to replace anyway. Have a look at the lamp base to verify they are in good condition also.

    Rust is a little more challenging requiring elbow grease and a wire wheel or sanding than HT paint. Otherwise you could if in-accessible try some rust reformer. Given a bond to the rust, I don’t expect the temperature will effect rust reformer paint much in making it peel as normal paint would to a non-rusted surface.

    I think they are a great thing, should give you hours of fun in making them work, what could be more fun for you? It’s not a moving light but should be fun all the same and if converted to Fresnel, might be useful depending upon the fixture design. I was never a fan of the grainy harsh beam provided by a PC unless it was an element of the design. Depending upon the PC of course if it can be converted. Some of the longer throw fixtures look more like a carbon arc follow spot than a Fresnel which I would assume to have too narrow a beam spread.

    Moonshadow Never heard of them before, than again while Harmony and Minuet as names sound familiar, I can’t say I have ever seen anything by them either.

    As for effort, I would not throw them out. If you don’t plan to use them for stage lights, you might wire and yoke them and use them for backstage work lights. Given a lack of lens, the body acted as a good baffle for the light and the beam was still adjustable for beam angle. One place I worked did this with some success.
     
  3. dj_illusions

    dj_illusions Active Member

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    Location:
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    thanks ship, that information is fantastic.
    i will get a picture of them, and try and get some measurements and go from there.

    thanks for your help!
     

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