image circles for medium format 645 for 6x7?

Discussion in 'Medium Format Cameras and Accessories' started by ghost1001, Mar 6, 2008.

  1. ghost1001

    ghost1001 Member

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    Hi All,

    This is related to my question yesterday about how to cock and fire medium format leaf shutter lenses.

    Ok...so the RB lenses will cover up to 4x5 with the longer lenses having more than enough image circle; will the image circle always incearse with focal lenght?

    The reason I ask ist that I am now looking at 645 lenses for my project, specifically the Mamiya 645 LS (leaf shutter) lenses.

    I want to use these to cover 6x7 format and I am assuming if the BR 6x7 lenses will cover to 4x5, then the 645 lenses may cover 6x7.

    In any event I have a 645 70mm LS lens in my posession. How do I check the image circle for this lens. I do not have a view camera to mount it on, but can probably jury rig something.

    Suggestions please.

    PS, I am looking at the 645 lenses now because they focus, the RB leses do not, and I want the body of my camera to be fixed (no bellows)

    Thanks
    Kevin
     
  2. Jeff Searust

    Jeff Searust Member

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    So the 645 lenses also have the shutter integral to them? Like the RB 67 lenses?

    I have taken the front section of an RB67 off and mounted it on a 4x5 lens board where I can use these lenses, as well as being able to cock them. But using 645 lenses that the focus and shutter are in the lens might be fun.
     
  3. ghost1001

    ghost1001 Member

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    Hi Jeff,

    Some do, they make LS (leaf shutter) leses for the 645. Specifically, 55mm ls, 70mm ls, 80mm ls and 150mm ls. They are so you can sync your flash at all speeds on the lens. They are more compact but they will not have the coverage of the RB lenses, hence the question above.

    I think these will great for a camera project I want to build.

    Kevin
     
  4. Dan Fromm

    Dan Fromm Member

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    Kevin, ask your 70 mm LS lens for the 645 how much it covers. Don't make assumptions about it or other lenses for the 645 that could be wrong. Remember that the lenses don't have to cover more than ~ 70 mm and that the designer/manufacturer have no incentive to design/build lenses with more.

    And don't make the mistake of assuming that the circle illuminated is the circle of adequate sharpness (covered). The only way to assess coverage is on film. Looking at the GG or at an image cast on the wall won't do. Sorry 'bout that, but that's how it is.

    Cheers,

    Dan
     
  5. ghost1001

    ghost1001 Member

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    Hi Dan,

    So I need to have the lens put in a LF camera set the lens to infinity and shoot on at least, say, a 4x5 film and then judge form that, correct. And also have the lens at the proper distance to the film plane.
     
  6. MattKing

    MattKing Subscriber

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    Another thing to watch for is that some of the Mamiya 645 lenses have an internal baffle that restricts the angle of view/illumination. I expect that they are there to control flare, but as a result the lens has a film plane "output" which is rectangular, rather than round.

    Matt
     
  7. Dan Fromm

    Dan Fromm Member

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    Exactly. Then look at the circular (or partly circular image) with a strong magnifier and decide where the sharpness ends. This needs a target that has fine detail all the way across. A brick wall might (great stress might) do.

    I wish there were an easier cheaper way.

    Cheers,

    Dan