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Thread: What is a A. J. Thompson & Co Petzval lens about?

  1. #1

    Join Date
    Nov 2008
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    The Desert * Phoenix AZ
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    133

    What is a A. J. Thompson & Co Petzval lens about?

    Hi Eveyone,
    I have a lens & camera that is part of a Learning Channel program I am working on about Wet Plate & the cameras they (we) use.

    So the producer sends me an 8x10 camera (he got at auction)
    that needs some love in terms of wood work & bellows. So I'm looking for anything you guys and gals may know about restoration of this period stuff.

    But the big question I have in about the lens:

    A.J. Thompson & Co : Importers : Boston

    It seems like a 10" Magic Lantern lens because it is without a slot for stops. It has a 10" distance from the rear element to the paper when focused at infinity and a 76 mm rear element diameter, and is 150mm from front lens to back lens. Is this how you can somehow find the speed? And the flange as "France" stamped on it.

    I have removed the 2 cells but have not been able to get the glass out of the brass to clean it. Any ideas??

    Any info, stories & lore would be great.

    I'd also like to get a ballpark value for a lens like this. The glass is a bit dirty but seem like a cleaning would clear that all up. The brass is ok and the flange is with it.

    Thanks for reading this far!

    Steve

    PS Jim & Eddie HELP !!!!! hahahahaha






  2. #2
    Mark Sawyer's Avatar
    Join Date
    Jul 2004
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    Stuck inside of Tucson with the Eastern Seaboard Blues again...
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    5,627

    Re: What is a A. J. Thompson & Co Petzval lens about?

    Such a coincidence! Today and last weekend, I was working with an A.T. (not A. J.) Thompson lens on some half-plate wet plates! I was using my smaller one, about an 8" f/4.6 that's 110mm long overall (90mm lens-to-lens) with a 160mm back focus, but I also have a larger approximate 10" f/5 A.T. Thompson that's 160mm long overall (115mm lens-to-lens) with a 180mm back focus. They look very much like yours, but a little smaller.

    These are indeed magic lantern lenses, and I think they're quite nice little Petzvals. Garrett ("goamules" on this forum) was over today, and thinks these are Darlots by some of the hardware on them, and I tend to agree. The Vademecum doesn't mention them.

    The distance from the back element to the plate is the "back focus", not the focal length, which is about from the plane of the f/stop (if it had one) to the film. I'd guess it would be maybe 1/2 an inch behind the focusing wheel's axle, but it's hard to say, as it was moved around on different lenses to flatten the field and reduce pin-cushion and barrel distortion.

    To find your f/stop, measure the lens' inner diameter through the front element, and divide the focal length (not the back focus) by that inner diameter.
    They aren't particularly rare or distinguished, (although I like mine!), and should only be worth $100 - $200 in the condition yours is in, but these are the days of Petzval-Madness, so that could easily be tripled on the right day.

    Some images from my little one:





    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  3. #3

    Join Date
    Sep 2007
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    AZ
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    4,149

    Re: What is a A. J. Thompson & Co Petzval lens about?

    Like Mark said. But also a clue to it being a magic lantern is that the lettering is written so that it can be read when the focus knob is on top. This is how they are typically positioned, it's easier to grab on top. Why did the focus knob on camera lenses move to the bottom (though the very early ones were on top sometimes too)? Because waterhouse slots came along and you couldn't have the stops falling out....so the knobs were moved to the bottom. But Magic Lantern lenses didn't need to change. The lettering isn't always this way, but often is.

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