Mamiya RB67 Split Image Screen Focus Issue

Discussion in 'Medium Format Cameras and Accessories' started by houdel, Aug 18, 2013.

  1. houdel

    houdel Member

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    I recently installed a split image focus screen on my Mamiya RB67. I was quite disappointed with the first pics I took using this screen, my subject was out of focus but the near background was in perfect focus. Picture 1 is one of the pics I had the problem with, an outside statue of Madonna at a local church. This focus screen is a vertical split image, unlike most split image screens which are horizontal split image, so I had to focus on a horizontal feature line. In pic 1 I focused on a small "knot" in the center of the robe, visible at the top left of the pic (the pic is a crop of the original image blown up to "pixel size" in PSE 11). I was careful to focus properly on the "knot" and adjusted the lens floating element to the correct distance, about 20-30'.

    Picture 2, of some stonework on the side of a building, was taken the same day with the same lens and is in perfect focus. Subject distance here was about 8'. Again, a crop at "pixel size" in PSE 11.

    Picture 3, same subject as picture 2, taken with my Canon EOS 20D at the same time, also a "pixel size" crop, for reference.

    All three pics I took of the statue had the same focus issue. I did use two cable releases to flip the mirror up and paused a few seconds before tripping the shutter. I am fairly certain I was accurately focused on the statue, so what went wrong? Operator error (maybe I accidentally moved the focus knob after initially setting the focus)? The stonework was in perfect focus, why not the statue? All my pics with my old matte screen were properly focused, is some sort of focus alignment required when changing focus screens?
     

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  2. KennyMark

    KennyMark Member

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    Hi Houdel,
    The cause of this symptom could be one of the following:
    1) focus position adjusted following initial focus determination (possible and likely)
    2) focus screen not mounted properly (possible but not likely, you'd probably notice this before replacing the finder)
    3) lens not mounted properly on body (possible but not likely. The lens mount could be damaged, the lens flange could be damaged, both of which you would probably notice upon visual inspection)
    4) lens could be damaged (possible but not likely, you'd get the same results with another focusing screen unlike your results with another focusing screen)
    5) focusing screen is damaged (possible but not likely, you'd almost certainly notice this)

    What you are experiencing is the result of the lens being focused on a plane beyond the desired point from the camera. This means that infinity is being pulled further from the focusing screen than what you see visually. In other words, the film plane is closer to the lens than the focusing plane that you see when looking at the focusing screen.

    This means that the focusing screen is higher in the camera body than it should be, you believe that you're focusing closer than you really are.

    I'd check to make sure that the focusing screen is a) not damaged, b) mounted properly on the body. Playing with my RZ that I have with me, it is possible to put the finder on without having the focusing screen seated properly in the camera.

    On the other hand, I have bumped the focusing knob on occasion if I did not employ the lock.

    Let us know what you find.

    Kenny
     
  3. MattKing

    MattKing Subscriber

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    Is there any chance that the focus screen you have is for a different model of the RB67?

    Or even for the RZ67?

    I'm not handy to my various Mamiya links, but I would look for a Mamiya System page that corresponds to the version of the camera you have, to see if the split-image screen is the right one.
     
  4. houdel

    houdel Member

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    This seems to me to be the most likely.

    The focus screen just drops in, can't put it in upside down nor is there any form of adjustment. It can be rotated 180 degrees (Mamiya name at the front or rear when installed) but I see no visible difference either way I install it. Doesn't seem likely.

    I've taken 2 rolls of film with this lens, all came out perfectly focused except these three and one I know I forgot to focus. This doesn't seem likely either.

    No visible damage & it seems to be installed correctly. This doesn't seem likely either.

    I purchased this screen new from B&H Photo, it came in a Mamiya factory sealed box and the box is marked "RB67 Pro SD". The frame of the screen is marked only "Mamiya Japan", same as the old screen I took out. There always is the possibility the wrong screen got stuffed in the box at the factory.

    Well all I can come up with is operator error. Not MY error of course; I had an untrained female assistant helping me when I was taking these photos. Most likely SHE did something when I wasn't looking. I guess all I can do is shoot another roll of film, including the statue again, taking care that my focus is spot on before I shoot. Then, assuming all the new images come out properly focused, soundly cuss out my assistant! I will post the results here once I get the next roll of film back.
     
  5. Xmas

    Xmas Member

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    Which screen do you have?
    the RB67 ProS
    no 3 screen is a horizontal split but it is all matt and you can focus away from the split
    no 6 screen is a 45 split surrounded by doughnut micro prism and rest of screen matt for focus
     
  6. houdel

    houdel Member

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    Type "B" - it is the only split image screen listed at either Adorama or B&H.
     
  7. MattKing

    MattKing Subscriber

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    After I made my last post I sought out the legacy information on the Pro SD from the Mamiya/Leaf site. This is what it says about screens:

    Vertical Split Image
    Same as Matte, but with a vertical central split-image rangefinder wedge added. Matte surface can be used for focusing, but the vertical split-image feature makes focusing easier and more accurate for subjects such as portraits.
    Cat. # 214-527

    Matte
    All matte with Fresnel lens, suited for general purpose photography. (Supplied with camera)
    Cat. # 214-520

    Checker
    Same as Matte, but with perpendicular grid. Pattern ideal as a compositional aid. Grid intersections also useful as reference points for multiple exposures.
    Cat. # 214-521

    Microprism
    Same as Matte, but with central microprism spot added. Provides an alternative Rangefinder Spot screen with same benefit of enhanced focusing precision.
    Cat. # 214-523

    Cross Hair
    All matte screen with small aerial (totally transparent) spot with cross hairs. Used for parallax focusing and designed for special high magnification applications. Especially suited for macro and telephoto photography.
    Cat. # 214-524

    RangefinderSpot/Microprism
    Same as Matte, but with a 45° split-image rangefinder wedge surrounded by a microprism collar. Highly versatile 3-way focusing (rangefinder, microprism, and matte). Ideal for general purpose photography.
    Cat. # 214-525
     
  8. Xmas

    Xmas Member

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    ok set the camera on tripod focus on old screen on high contrast target lock focus swap screens and check focus still same.
    if different send split screen back and ask for $.
     
  9. houdel

    houdel Member

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    Seems like a good idea. I'll try it once the sun comes up!
     
  10. paul ron

    paul ron Member

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    Possable you have to adjsut the focus of the screen to the film plane. Not all screen mounts are the same but to check it is fairly simple. A plain GG has no glass or fesnell adn the split has. mounts were also changed over the years as well.

    GG ont eh film gate wihtthe back open.. point the camera at a well lit target, focus the screen with a loupe. then check the GG onth efilm gate with the loupe.. if all is well.. enjoy your camera. If not then adjsutments are needed.

    The 4 large screws with the spanner holes are the height adjsutments. Before you move or do anyting.. make a small scratch in each in reference to a screw or a stationary part of the body.

    By lifting the screen to see if the height has to go up or down will determine which way the screws all get turned evenly the same amt. Check the GG often n make sure you are writing then how many tunrsthe screws got.. amazing how fast you can get confused.

    If you are not comfortable doing this send the camera out for adjsutments.

    This is a commong problem when using the brite screens then going back to the old style. .different thickness n variations change the focus.