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Thread: B&L 18in Petzval Projection Lens

  1. #1

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    B&L 18in Petzval Projection Lens

    I am cleaning the glass of a B & L 18in petzval projection lens. I think it's an F8.
    When disassembling the rear element I find the flint and the crown.
    Flint inside - Crown outside. It looks like the "original" configuration of a petzval.
    Between the flint and the crown there is no spacer ring, they are mounted one on top of the other and they seem to fit correctly.

    The question is:

    1.- Are they mounted in this way or is there a missing spacer ring between them ???.
    2.- In this lens, the configuration - flint inside / crown outside - is correct ???

    Thanks in advance...

  2. #2

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    Re: B&L 18in Petzval Projection Lens

    There should be a spacer, yours is missing.

  3. #3

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    Re: B&L 18in Petzval Projection Lens

    Quote Originally Posted by goamules View Post
    There should be a spacer, yours is missing.
    Thanks Garret.
    Do you have any of these ???
    Could you give me the measurements of the spacer ring ???

    ... (I was thinking, that by the curves of the elements (flint / crown) was a "Dallmeyer" design and had no spacer ring. In fact, although they are mounted one on top of the other, the centers of the elements do not touch each other and there seems to be air between them and maybe it was mounted upside down ...
    Totally wrong then...)

  4. #4

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    Re: B&L 18in Petzval Projection Lens

    I have successively made spacer rings by bending lengths of rectangular black plastic "rod" that is used by model Railroaders. Once cut to the correct circumference length, it stays inside the lens in a perfect circle by itself. Trick is to get the exact correct length.

  5. #5

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    Re: B&L 18in Petzval Projection Lens

    Quote Originally Posted by Greg View Post
    I have successively made spacer rings by bending lengths of rectangular black plastic "rod" that is used by model Railroaders. Once cut to the correct circumference length, it stays inside the lens in a perfect circle by itself. Trick is to get the exact correct length.
    thanks Greg
    The problem is that I do not know the thickness of the spacer ring.
    I think the correct distance between both elements will be important, or not?

    Flint and Crown fit perfectly in the brass housing ...
    Some photos ...
    Attached Thumbnails Attached Thumbnails B&L_18in.jpg   BL_Elements.jpg   Rear_Group.jpg  

  6. #6

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    Re: B&L 18in Petzval Projection Lens

    Anyone own one of these?
    Could take a look and tell me how the rear elements are mounted?
    ... and what is the spacer ring thickness if really there is one mounted between the flint/crown?

    Thanks in advance.

  7. #7

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    Re: B&L 18in Petzval Projection Lens

    What is the black ring in the middle in the second image ?

  8. #8

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    Re: B&L 18in Petzval Projection Lens

    Quote Originally Posted by Amedeus View Post
    What is the black ring in the middle in the second image ?
    Well, when I first removed the back cell I found this ring, then the flint, and then the crown.
    (from inside / outside the lens).
    Then I thought, another petzval badly assembled ...
    Then dismantle the front cell and found the same ring and the front achromat.

    These two rings act as "adjustment" of the elements of each cell. Assemble just before screwing the last ring that closes the housings and makes the flint/crown and achromat do not move and have no slack in their respective housings

    Searching and searching, I found this thread:
    https://www.largeformatphotography.info/forum/showthread.php?70668-Bausch-amp-Lomb-Projection-Lenses


    in which rob_gervais, exposes the following in post # 5:
    (I canīt see the images, it would help to know if the lens is like mine in 22in)

    I was not aware the cells would disassemble when I first received the lens. Looks like a Petzval design, all right, cemented pair up front, two in the rear. The only thing was the rear cell was assembled incorrectly. The layout of image 3 shows how the rear cell came apart - spacer, lens, lens. As a result, there is a mark in the center of one of the lenses - but I'm only going to shoot B & W, so I'm not sure it's too great an effect.
    The order of the elements is the same as the one I found. - ring, lens, lens -.

    Rub mark that he found, I think it was caused because the flint and the crown were incorrectly placed and rubbed against each other. (If you place them with the curves in the correct way, but without a spacer ring, they only touch very little on their outer edges.)

    I've reassembled the rear cell with the spacer between the lenses - but I do not know that the last lens will ever come out again, the spacer was a very tight fit.
    Maybe never come out again, is more, if you put this ring between the lenses and screwed the last ring that closes the housing, sure at least that lenses will suffer chips on the outer edges.

    I thought maybe this B & L did not have a spacer ring, but Garret's post has me puzzled.

    Many Thanks, Rudi. The mystery continues ...

  9. #9

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    Re: B&L 18in Petzval Projection Lens

    I believe you found your spacer.

    Just assembled wrong that's all

    Put it in between flint and crown and be happy. There is little sensitivity to spacing between front and rear elements in a Petzval, nothing I would worry about.

    Give it a try !

    Quote Originally Posted by C_M View Post
    Well, when I first removed the back cell I found this ring, then the flint, and then the crown.
    (from inside / outside the lens).
    Then I thought, another petzval badly assembled ...
    Then dismantle the front cell and found the same ring and the front achromat.

    These two rings act as "adjustment" of the elements of each cell. Assemble just before screwing the last ring that closes the housings and makes the flint/crown and achromat do not move and have no slack in their respective housings

    Searching and searching, I found this thread:
    https://www.largeformatphotography.info/forum/showthread.php?70668-Bausch-amp-Lomb-Projection-Lenses


    in which rob_gervais, exposes the following in post # 5:
    (I canīt see the images, it would help to know if the lens is like mine in 22in)



    The order of the elements is the same as the one I found. - ring, lens, lens -.

    Rub mark that he found, I think it was caused because the flint and the crown were incorrectly placed and rubbed against each other. (If you place them with the curves in the correct way, but without a spacer ring, they only touch very little on their outer edges.)



    Maybe never come out again, is more, if you put this ring between the lenses and screwed the last ring that closes the housing, sure at least that lenses will suffer chips on the outer edges.

    I thought maybe this B & L did not have a spacer ring, but Garret's post has me puzzled.

    Many Thanks, Rudi. The mystery continues ...

  10. #10

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    Re: B&L 18in Petzval Projection Lens

    Quote Originally Posted by Amedeus View Post
    I believe you found your spacer.

    Just assembled wrong that's all

    Put it in between flint and crown and be happy. There is little sensitivity to spacing between front and rear elements in a Petzval, nothing I would worry about.

    Give it a try !
    If I put the ring between the elements and close the cell I will damage the elements, for sure.

    As it came mounted (ring-lens-lens) the elements only touch each other very on the edge (+/- 1mm) and there is space between them on the rest of the surface. I tried it on the window with the cardboard and it seems that focuses mounted in this way ...
    I need a flange to be able to test it with the camera.

    Do you know any "petzval" that is mounted without spacer ring ??? ... (Element on top of element)

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