Thread: BMPCC4k - Follow focus body flex

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  1. #1 BMPCC4k - Follow focus body flex 
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    Here's an interesting one.

    I have my Pocket 4k mounted on a Berkey Systems baseplate with no cage. It's mounting an Olympus 2.8/12-40mm with 0.8 focus gear driven by a Chrosziel follow focus. The torque from the follow focus is actually flexing the carbon fiver body at the attachment point to the baseplate and you get a nice up and down tilt, depending on in which direction you are puling focus.


    This is not a problem if you are using something like a Speedbooster or PL mount adapter with a support foot.. This second attachment point prevents the body from flexing. Unfortunately this is not an option with the Olympus 2.8/12-40mm in native M43 mount.



    Anyone else seen this?

    Please tell me this doesn't happen once the camera is mounted in something like the SmallRig or Tilta cage.
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  2. #2  
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    This is indeed quite worrying if a follow focus is enough flex the plastic lens mount
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  3. #3  
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    Quote Originally Posted by Harry Lime View Post
    Here's an interesting one.

    I have my Pocket 4k mounted on a Berkey Systems baseplate with no cage. It's mounting an Olympus 2.8/12-40mm with 0.8 focus gear driven by a Chrosziel follow focus. The torque from the follow focus is actually flexing the carbon fiver body at the attachment point to the baseplate and you get a nice up and down tilt, depending on in which direction you are puling focus.


    This is not a problem if you are using something like a Speedbooster or PL mount adapter with a support foot.. This second attachment point prevents the body from flexing. Unfortunately this is not an option with the Olympus 2.8/12-40mm in native M43 mount.



    Anyone else seen this?

    Please tell me this doesn't happen once the camera is mounted in something like the SmallRig or Tilta cage.
    I think I'm gonna "YIKES!" on this one.

    Good thing I'm one who reeeeally likes his cameras properly caged.
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    Quote Originally Posted by DPStewart View Post
    I think I'm gonna "YIKES!" on this one.

    Good thing I'm one who reeeeally likes his cameras properly caged.
    But by the sounds of it even if the cameras in a cage it may still flex unless you have a speedbooster/ adaptor mounted to the cage also to keep it steady. A big problem for native lens shooters indeed.
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  5. #5  
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    Quote Originally Posted by Ryanite View Post
    This is indeed quite worrying if a follow focus is enough flex the plastic lens mount

    It's not the lens mount, which is made from metal. It's the carbon fiber body that is flexing around the bottom mounting point attached to a baseplate.
    Last edited by Harry Lime; 12-11-2018 at 09:27 AM.
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  6. #6  
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    Quote Originally Posted by Ryanite View Post
    But by the sounds of it even if the cameras in a cage it may still flex unless you have a speedbooster/ adaptor mounted to the cage also to keep it steady. A big problem for native lens shooters indeed.
    The camera has two mounting points, one on the base and the other where traditionally the hot shoe would be. If the cage engages both of these mounting points all should be well. (or if you re using a Speedbooster / lens adapter supported by the cage or a lens support on 15mm rods)

    But from the looks at it you can't pull focus with a follow focus on a cage-less camera without flexing the body shell. Maybe on a very small lens with no resistance. Maybe.

    This is really awkward.
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  7. #7  
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    Quote Originally Posted by Harry Lime View Post
    The camera has two mounting points, one on the base and the other where traditionally the hot shoe would be. If the cage engages both of these mounting points all should be well. (or if you re using a Speedbooster / lens adapter supported by the cage or a lens support on 15mm rods)

    But from the looks at it you can't pull focus with a follow focus on a cage-less camera without flexing the body shell. Maybe on a very small lens with no resistance. Maybe.

    This is really awkward.
    That's not awkward but to expected with MFT mount with a lot of play. There is a reason positive lock aka PL mount exists.
    I have the PCC4k in the 8sinn half cage and it works great - nothing at the cage flexes, but the lens itself because of the MFT mount. If you take the camera and a longer lens like the 12-60mm and put slight pressure below the lens you can see it wiggling in the mount.
    Got also the Metabones CINE EF mount with positive lock and there is no flexing whatsoever.
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  8. #8  
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    Quote Originally Posted by Robert Niessner View Post
    That's not awkward but to expected with MFT mount with a lot of play. There is a reason positive lock aka PL mount exists.
    I have the PCC4k in the 8sinn half cage and it works great - nothing at the cage flexes, but the lens itself because of the MFT mount. If you take the camera and a longer lens like the 12-60mm and put slight pressure below the lens you can see it wiggling in the mount.
    Got also the Metabones CINE EF mount with positive lock and there is no flexing whatsoever.

    It's not the lens mount that's flexing. The actually carbon fiber body shell is flexing around the bottom mounting point, causing a slight tilting movement.

    The lens may rotate slightly parallel to the surface of the mount. That is not good either but common for a spring loaded mount. This does not happen with a breech lock type of lens mount like PL or the heavy duty variants of E-mount and EF.

    You need a cage with attachment points at the top and bottom or a lens support to stop the body from flexing, when used with a follow focus.

    It's an engineering problem on the part of BM.
    Last edited by Harry Lime; 12-11-2018 at 10:55 AM.
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  9. #9  
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    So Harry, as you discovered, the camera was not designed to be used with a big lens and rigged with a follow focus without being in a cage. This is not an engineering failure, but a choice to keep the camera light weight.
    The camera was designed more use with native MFT lenses using auto focus or manual focus with you hand on the lens, DSLR style.

    As you mentioned, for rigging this camera out, you need to put it in a good cage. This was true of the original Pocket camera, and the Micro cameras. All could be used naked, but not with long or heavy unsupported lenses.
    Cheers
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  10. #10  
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    Quote Originally Posted by Denny Smith View Post
    So Harry, as you discovered, the camera was not designed to be used with a big lens and rigged with a follow focus without being in a cage. This is not an engineering failure, but a choice to keep the camera light weight.
    The camera was designed more use with native MFT lenses using auto focus or manual focus with you hand on the lens, DSLR style.

    As you mentioned, for rigging this camera out, you need to put it in a good cage. This was true of the original Pocket camera, and the Micro cameras. All could be used naked, but not with long or heavy unsupported lenses.
    Cheers


    Denny, it's mounting an Olympus 12-40, which weighs next to nothing. It's not the weight of the lens that is the problem. The problem is that the carbon fiber shell is very thin and does not appear to be reinforced internally. It does not have sufficient stiffness to stand up to the torque generated by the follow focus and the shell flexes against the mounting screw in the base of the body. Thats an engineering problem, not operator error. No big mystery here, just physics 101.

    If you stick it in a cage that is attached to the camera body by both the top and bottom mounting points everything is fine. I have a cage on order.

    Same for a support foot with lens adapters or lens support.

    I have mounted my s16 Zeiss Super Speed mk III via the Wooden Camera PL adapter and secured it with a lens support and it eliminated the flexing problem.
    These lenses weigh more than the camera, but he support foot takes the strain off the body mounting point. But again, it's not so much the weight of the lens, but the torque generated by the gearing ratio of the follow focus.

    Regardless, anyone trying to use a follow focus without a cage or support foot is going to be in for a surprise.
    Obviously pulling focus on the Oly 12-40 without the follow focus does not cause the flexing problem.
    Last edited by Harry Lime; 12-11-2018 at 03:16 PM.
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