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Thread: Rodenstock Imagon needs an f stop scale

  1. #1

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    Rodenstock Imagon needs an f stop scale

    I've inherited a 250mm Rodenstock Imagon in a Copal 3 shutter. It's missing the f stop scales. I know that SK Grimes can probably fabricate one, but does anyone know how I might get Rodenstock to help me?

    Thanks!

  2. #2

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    Re: Rodenstock Imagon needs an f stop scale

    Imagons are intended to be used with the iris diaphragm wide open, and one of several perforated disks attached to the front. These disks are marked in "H" stops (corresponding to f/ stops) for exposure control, but the patterns and sizes of the perforations are used to achieve different soft-focus effects.

    That said, you can in fact use the shutter diaphragm, and at small f/ numbers the lens is actually a fairly decent "conventional" optic. I seriously doubt that Rodenstock offers anything that will help, although you might be able to get a set of replacment disks from them.

  3. #3
    Michael Jones's Avatar
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    Re: Rodenstock Imagon needs an f stop scale

    I don't believe they had scales. The diffusion disks are calibrated in "H" stops roughly corresponding to f-stops. (And yes, I have a copal 3 mounted Imagon – no scales).

    Adam at SK Grimes is your best bet.

    Maybe Bob Solomon will post an authoritative answer.

    Good luck.

    Mike

  4. #4

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    Re: Rodenstock Imagon needs an f stop scale

    Thanks for your responses.

    I always thought that the lens was intended to be used wide open. And I have a set of disks. But there is a lever that stops down the diaphram, and there are small, machined holes at the top and bottom of the shutter that are spaced in a way that looks like it should have a scale plate..

  5. #5

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    Re: Rodenstock Imagon needs an f stop scale

    Imagons do not use the shutter's aperture blades so the shutters do not have an aperture scale. The Imagon casts multiple images on the film to get its effect. The main image from the center of the lens and the other image from the outside area of the lens. By using the shutter's aperture you change the effect by blocking the outside rays.

    The Imagon came with 3 disks, a ND filter and a lens hood. The factory no longer lists any of these accessories and we only have a couple of disks left from the 300mm Imagon.

    The ND filter was the way that you controllled exposure with the disks. Each of the 3 disks had a progressively larger center hole and adjustable outer holes. The softest possible effect was with no disk. That was an H stop of 5.8. The disk with the largest holes with the outer holes open was also 5.8 but a little sharper. Then next was that disk with all outer holes closed. The middle size disk with all holes open gave the same H stop as the first disk with all holes closed and so on. Once you found the effect you liked you could use the ND filter to reduce the amount of light reaching the film to maintain the same H stop.

    The effect was accomplished with the disk and setting of the holes used, the type of reflectors used (no umbrellas please) and the contrast ratio used (preferably about 5:1). The Imagon depends on strong spctral highlights melting into the shadow areas for the blooming effect of the Imagon. When the smallest disk opening was used with all outside holes closed the Imagon was a pretty sharp lens as it only used the central portion of the lens.

    The three disks have H values as follows:

    5.8 to 7.7, 7.7 to 9.5 and 9.5 to 11.5. These were the disks for the 200 and 250mm versions. The 300mm in Copal 3 shutter could only use 7.7 to 9.5 and 9.5 to 11.5. The opening in the 3 size shutter was too small to allow a 5.8 to 7.7 disk to be used. So the H value of a 300mm Imagon in a 3 size shutter without a disk was H6.8.

    Any other questions on the lens?

    Oh yes, the 200mm was for 6x6 to 6x7/6x9cm roll film. The 250mm was for 4x5 and the 300mm was for 5x7 film.

  6. #6

    Re: Rodenstock Imagon needs an f stop scale

    Bob, of course, is correct. Imagon lenses never had an aperture scale on the shutter, rather they are used with H-Disks and were never intended or designed to be used with a the shutter's diaphram.

    That said, as you have noticed the Imagon lenses usually come in regular shutters, so they have an iris as well as the fittings for aperture scales. However, although Bob will (correctly) tell you they are not designed as such, I have used them with the shutter's diaphragm and have lived to tell the tale.

    There are a few problems with using the diaphram; first, the lens was designed for a iris where the H-Disks sit, that is slightly off of the shutter's diaphragm. I am not completely sure of what results this will have. Also, since the lens has lots of built-in halation, it may cause a slight over exposure, if the "correct' f-stops are used. And yes, SK Grimes can engrave them for you.

    Quote Originally Posted by Robert Kalman View Post
    Thanks for your responses.

    I always thought that the lens was intended to be used wide open. And I have a set of disks. But there is a lever that stops down the diaphram, and there are small, machined holes at the top and bottom of the shutter that are spaced in a way that looks like it should have a scale plate..

  7. #7

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    Re: Rodenstock Imagon needs an f stop scale

    The softest possible effect was with no disk. That was an H stop of 5.8. The disk with the largest holes with the outer holes open was also 5.8 but a little sharper.
    For the 250 which I also have is it not H 5,8 without the disk, it is exatly f 4,5 and yes it is the softest one.
    I do often use it without the disks because I do not so like the Kühne Stars in high lights! So I do use very seldom fully open but at arount f 5.6-8 which I marked with my Broncolor FMII Probe it gives me a very nice SF effect not the original Imagon effect but also a very nice one.

    Cheers Armin

  8. #8

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    Re: Rodenstock Imagon needs an f stop scale

    My 300mm came with after market engraved f stops on it's compound shutter and the effect of the lens, in portraiture, used without h-discs, but using the compound shutter, is nice; different and exaggerated but worth trying. Very glowy at 4.5 much less at f8
    Regards
    Bill

  9. #9

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    Re: Rodenstock Imagon needs an f stop scale

    Quote Originally Posted by Bob Salomon - HP Marketing View Post
    ...the type of reflectors used (no umbrellas please)...
    Hi Bob!
    Could you please give a bit more detailed comment?
    Personally I don't like umbrellas and always prefer soft boxes for soft lighting. But I'm very curious about your reservations against umbrellas exactly in context of Imagon.

  10. #10
    W K Longcor
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    Re: Rodenstock Imagon needs an f stop scale

    Quote Originally Posted by Andrey Vorobyov View Post
    Hi Bob!
    Could you please give a bit more detailed comment?
    Personally I don't like umbrellas and always prefer soft boxes for soft lighting. But I'm very curious about your reservations against umbrellas exactly in context of Imagon.
    I am not Bob, but I'll try and explain what he was saying, and he can correct me later if needed. Don't use umbrellas OR soft boxes if you want the great "sparkling" effect of the Imagon. Using more direct or contasty lighting with a higher ( Bob says 5:1) contrast ratio will cause the bright highlights to flair into the shadows. Actually, each and every one of the little apeatures surounding the large central opening in the disks will produce a secondary and out of register image on top of the main image. Since the aperatures are smaller, they produce less exposure than the main aperature -- giving mostly an image of the brightest parts of the lit subject. The effect is a very pleasant ( if done correctly) glow effect. But -- soft lighting will not do the job because there is no specular highlight and no deep shadow for the flair to "glow" over.
    If I have made you more confused - sorry. The best way to learn about an Imagon is to expose lots of film. Have fun!

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