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  1. #11
    Monophoto's Avatar
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    Similar question came up the other day on LF Forum, and Bruce Barlow noted that Richard Ritter uses plexiglass as the standard 'ground glass' in his ULF cameras. Sand King jumped in to say that the experience he has had with a RR camera is that the plastic GG is just as good as regular glass, plus it's lighter in weight and unbreakable. The only downside is that plastic can be attacked by some solvents (which probably shouldn't be allowed within five miles of a good camera anyway), and can scratch.

    Ritter gave a presentation at the 2005 LF Conference on quick and dirty field repairs in which he suggested that if you break your ground glass while traveling, just whip into a Walmart to buy a cheap plastic hoto frame of the appropriate size, and a package of fine sandpaper, then sand the plastic from the frame to make a replaceable ground glass.

    I purchased a fresnel from Calumet for my Zone VI lightweight. The fresnel/ground 'glass' is actually plastic, but there is a thin cover glass to go over it. But the image is actually formed on the plastic fresnel/ground glass.
    Louie

  2. #12

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    Quote Originally Posted by Steve Smith View Post
    Lexan is available with a fine textured surface which I have used in place of ground glass.
    Steve, do you know the designation code of this type of Lexan? Is it a General Electric / Sabic product or perhaps a different type of polycarbonate? Is it available in 3mm thickness? Did you have to sand it further lightly with 800 & 1000 water-type grit paper?

  3. #13

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    Richard is a big believer in plexi GG's for big cameras. Glass shards and big expensive bellows don't play together very well if the GG breaks.

    I've used the gallery's RR 7x17 with a plexi screen, it works fine, there is no practical difference between it and a glass one.

  4. #14
    Steve Smith's Avatar
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    Quote Originally Posted by darkroom_rookie View Post
    Steve, do you know the designation code of this type of Lexan? Is it a General Electric / Sabic product or perhaps a different type of polycarbonate? Is it available in 3mm thickness? Did you have to sand it further lightly with 800 & 1000 water-type grit paper?
    http://www.cadillacplastic.co.uk/pro...raphics-films/

    Anything designated 'fine' will probably work. Velvet is a bit coarse.

    I used it as is with no further treatment.

    EDIT: Or see my previous post in this thread...

    Cadillac: http://www.cadillacplastic.co.uk/

    Plastic Technology Service Ltd: http://www.ptsuk.com/ - Polycarbonate here: http://www.ptsuk.com/longhua.html (PC813F).

    A similar product but in polyester is available from Autotype/McDermid: http://www.macdermidautotype.com/

    We only use these materials up to 0.25mm which is a bit too thin for focusing screen use (although I have used it) but most are available at least up to 1.5mm.

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  5. #15
    Newt_on_Swings's Avatar
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    In the back of my wista is a piece of clear lexan as a protector for my plastic fresnel. It's also etched with an exacto to show grid lines and highlighted with different color fine point sharpie to mark out 6x7 and fuji instant sizes on their specific holder templates. Works well for me.

  6. #16

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    Steve, thanks for the answer. I just found this type as well:

    http://www.roberthorne.co.uk/product...rbonate-sg305/

    Seems to me the 88% transmission may be a little too high, but otherwise it looks promising.

  7. #17

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    Just finished an 11X14 camera build and used a Plexiglas screen with a Fresnel lens laminated on it from a projection TV set.Lightly sanded the side opposite the Fresnel and installed,works great.If you can salvage these from an old TV size won't be an issue, as I cut mine down from a 1/8" thick 52" screen.
    Luck,
    Don

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