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Thread: Process lenses

  1. #51
    Drew Wiley
    Join Date
    Sep 2008
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    SF Bay area, CA
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    10,592

    Re: Process lenses

    Variations in film flatness in a typical holder pretty much renders option no.3 unrealistic.

  2. #52

    Re: Process lenses

    Real "Process" cameras have precision vacuum film backs to assure that big sheet of film is flat.

    Typical view camera film holders can never approach this degree of film flatness... and camera alignment has not been discussed yet.

    Real "Process cameras" are very much a different breed of camera.


    Bernice


    Quote Originally Posted by Drew Wiley View Post
    Variations in film flatness in a typical holder pretty much renders option no.3 unrealistic.

  3. #53

    Join Date
    Jul 2016
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    1,217

    Re: Process lenses

    Quote Originally Posted by Drew Wiley View Post
    Variations in film flatness in a typical holder pretty much renders option no.3 unrealistic.
    Hello Drew,

    This should be discussed...

    I may be unrealistic with diafragm wide open, but if stopping (say to f/16) then DOF in the film plane increases, in the same way that it increases in the scene field, a math formula describes that.

    At the end the inter-cell spacing optimization won't be seen if the lens is not working in a sweet aperture point, what I mean is than if the lens has too much diffraction or too much spheric aberration (because too open) then you won't see the inter-cell spacing optimization.

    As allways, sharpness can have a number of limitating factors, the one that has more impact it masks the others.

    Also for extra film flatness I use a very easy trick, I place a 9x12cm sheet in a 4x5" holder, in this testing holder I sprayed 3M Re Mount glue, so the sheet is pretty adhered to the back. Well, it is not a precission holder, but at least you completely avoid any sheet curvature impact.

    At one time I had a box of 912 sheets but I only had 45 holders... so the trick came from that.

    Also I checked well my 45 Norma alignment, I've it very tight and lubed. Well, Normas still are precission gear in this 2017. I'd strongly recommend a lube for it: Interflon FoodLube (oil, not grease). Being H2 atoxic grade, it has very high performance for that. Every movement skids like new or better: No real need for geared movements.

    Regards

  4. #54
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    10,592

    Re: Process lenses

    I use 8X10 adhesive holders for images intended for significant enlargement. For diagnostic testing or critical duplication work I do have an all-metal precision holder. I test camera backs using precision flat stock with a depth micrometer. I took my Norma for a pleasant walk today and noted the need to tighten a couple of tiny set screws. That's a positive feature in my opinion. With the subsequent F-Sinars you have to add or remove shims.

  5. #55
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    10,592

    Re: Process lenses

    Forgot to state that my all-metal holder is indeed vacuum.

  6. #56

    Join Date
    Jan 2006
    Location
    Tucson AZ
    Posts
    1,281

    Re: Process lenses

    Once upon a time I was thinking of getting a real process camera. Can't quite remember why, but I was pretty serious about it. If I hadn't had to move for work I might have done it.

  7. #57

    Join Date
    Jul 2016
    Posts
    1,217

    Re: Process lenses

    Quote Originally Posted by Drew Wiley View Post
    I use 8X10 adhesive holders for images intended for significant enlargement. For diagnostic testing or critical duplication work I do have an all-metal precision holder. I test camera backs using precision flat stock with a depth micrometer. I took my Norma for a pleasant walk today and noted the need to tighten a couple of tiny set screws. That's a positive feature in my opinion. With the subsequent F-Sinars you have to add or remove shims.
    Hello Drew,

    I did not know that adhesive holders existed... you know, I'm a learner. I feel very lucky to have the chance to comment all that with proficient people, so what my learning is checked. Thanks for it.

    Regards,
    Pere

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