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Thread: Please help to determine the French lens maker.

  1. #1

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    Please help to determine the French lens maker.

    Hello!
    Has anybody know the French lens maker named DY? The lens is engraved "Brevet d Invention DY Paris". This is a convertible Petzval-type lens, each element mounted by bayonet and the front achromatic doublet can be used as a landscape lens. Rack and pinion mechanism is present, so it's an earliest Petzval lens, as I can estimate. The place for washer stops is present too. Estimated focal length is 220 mm and wide open approx. 4. Any information will be helpful, thanks.

  2. #2

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    Re: Please help to determine the French lens maker.

    Derogy, Derogy or Derogy!
    Letters and Bayonet systems.
    But will check VM so I havn't made a mistake.

    The "place for washer stops" looks like it was the mount for additional central lenses, both + or -, which could change the focal length.
    VM confirms what I said. In fact it has quite an extensive description. No mention of the DY abbreviation - these have no serial number, that came later!
    Last edited by Steven Tribe; 5-Mar-2012 at 03:45. Reason: VM data added

  3. #3

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    Re: Please help to determine the French lens maker.

    Thank you Steven! Of course DerogY, I'm so stupid.

  4. #4

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    Re: Please help to determine the French lens maker.

    Please, please post lots of detailed photos, if this is yours, as it will be of interest to us who have never seen one - or have who the other later types of bayonet Petzval caskets/convertibles!

  5. #5

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    Re: Please help to determine the French lens maker.

    just a minute

  6. #6

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    Re: Please help to determine the French lens maker.

    here are photos:

    Click image for larger version. 

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  7. #7

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    Re: Please help to determine the French lens maker.

    close-up

    Click image for larger version. 

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ID:	69570

  8. #8

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    Re: Please help to determine the French lens maker.

    Click image for larger version. 

Name:	derogys3.jpg 
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ID:	69571

  9. #9

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    Re: Please help to determine the French lens maker.

    Some pretty unique brass work here. Is the "ring" to support extra disc stops/lenses in the middle? Screw or also bayonet?
    The middle lenses were also achromats according to VM lens sketch (Der 01) mounted in front of the central stop.

  10. #10

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    Re: Please help to determine the French lens maker.

    Yes, the ring holds the diaphragm disc, but simply by press, without any screw or bayonet.

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