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Thread: Phase 120mm macro with DB vs Film back exposure problems

  1. #1
    New Member StoneNYC's Avatar
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    Phase 120mm macro with DB vs Film back exposure problems

    I was shooting some macro work with my DB and switched to my film back.

    When I did the exposure tests on the digital back everything was fine, but the film images are all thin.

    I got much closer when I was shooting the film images and so the barrel was extended almost fully.

    Is there some kind of "bellows" compensation needed?

    I developed the film with other images from other shoots using my RZ67 Pro II in the same development batch and those are all fine. It was only the macro images with the 120 lens that were an issue.

    I was using profoto strobe lighting and everything was controlled besides the barrel being almost fully extended for the film back images. So... is there some kind of "barrel draw" compensation I'm supposed to be making?

    What am I missing? Thanks!

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    Senior Member chrism's Avatar
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    Re: Phase 120mm macro with DB vs Film back exposure problems

    I've no experience of that gear, but it's absolutely correct that if the distance from the optical centre - roughly the plane of the aperture blades - of the lens to the film is greater than the focal length of the lens the effective aperture is smaller than advertised. So, yes, I imagine bellows correction would be needed in that situation, especially if you need very accurate exposure as for slide film. I guess the quickest way to find out would be to use the digital back but get as close to a subject as you did with film, and see if the images are underexposed.

    BTW, I've just discovered the iPhone app Reciprocity Timer and find it calculates bellows compensation for me.

    Chris

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    New Member StoneNYC's Avatar
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    Re: Phase 120mm macro with DB vs Film back exposure problems

    Quote Originally Posted by chrism View Post
    I've no experience of that gear, but it's absolutely correct that if the distance from the optical centre - roughly the plane of the aperture blades - of the lens to the film is greater than the focal length of the lens the effective aperture is smaller than advertised. So, yes, I imagine bellows correction would be needed in that situation, especially if you need very accurate exposure as for slide film. I guess the quickest way to find out would be to use the digital back but get as close to a subject as you did with film, and see if the images are underexposed.

    BTW, I've just discovered the iPhone app Reciprocity Timer and find it calculates bellows compensation for me.

    Chris
    Thanks for the reply.

    I recently sold the digital back so I can't do a comparison anymore.

    I have that app for my large format work and it's very accurate, I just thought that most macro lenses without bellows didn't need this. I've never needed it before with any other macro lens I've owned.

    Thanks anyone else who has this setup/lens and has some insight. It is of course entirely possible I messed up somewhere, but I just don't think I could have with 2 shoots when all my other shoots were fine with my other camera. Mistakes do happen of course.

  4. #4
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    Re: Phase 120mm macro with DB vs Film back exposure problems

    Of course you have bellows factor in ANY lens at any distance closer than infinity, but it's not noticeable until you get close enough to have a visible effect. In the film era my RZ's had a bellows factor printed on the distance scale on the side of the bellows. My ancient Nikon F4 with the data back would actually show you the readout changing as you focussed the macro lens to 1:1.

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