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GX7 "Chassis Stiffness" Issue on Tripod?

Discussion in 'Panasonic Cameras' started by oldracer, Jun 17, 2015.

  1. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    In an attempt to improve my tripod setup I just bought an Acratech GPS ball head on eBay to replace the Benro B1 that came with my travel tripod. In the process I have discovered a problem that is common to both of my two GX7 bodies:

    With the camera on my big 3-series Gitzo, well clamped down, and with everything tight, I zoom my 14-140mm to 140 and look at a lens test card that is across my shop. Attempting to wiggle the camera by wiggling the Arca clamp or anything else below the clamp produces almost no motion. Wiggling the camera body or, worse, the end of the lens produces big changes. When the balll head friction is set to barely hold the camera from flopping over, any attempt to adjust the center point of the image by moving the camera body results in the body flexing and rebounding when the movement pressure is released. Even at the 140mm zoom it is enough to be a problem. I dread doing the same testing with my 100-300mm.

    Bottom line, it appears that the tripod screw base in the camera is not solidly connected to the lens flange. Naive guy, maybe, but I would have expected that tripod socket to be machined into the same block of metal that comprises the lens flange.

    A partial workaround is to aim the camera by gripping the Arca clamp, putting no pressure on the camera body. The floppy body, though is probably the reason I have seen a small shutter shock effect when testing on my Gitzo 3-series/Studex.

    Has anyone else seen this? Or are you interested enough to do a quick test of your GX7 body? Just clamp it down tight on a tripod and, using a long lens, wiggle the body and see if the aim point moves. I want to hope that my experience is unusual, but with two bodies behaving exactly the same way I am pessimistic.

    Edit 6/20/15: Sorry I did not make it clear in this thread that I am dealing with vertical (pitch axis) motion -- like you get by moving the end of the lens up and down. Yaw axis motion (left/right movement of the image center point) is not an issue.
     
    Last edited: Jun 20, 2015
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  2. gr6825

    gr6825 Mu-43 Veteran

    277
    Oct 10, 2012
    What kind of camera plate do you have? If you are going to be doing critical tripod work, I recommend you look at one of these: http://www.reallyrightstuff.com/BGX7-Plate-for-Lumix-GX7.html

    I think for a compact camera like the GX7, your build expectations may be a little too high. Ain't no block of metal in there :)
     
  3. gr6825

    gr6825 Mu-43 Veteran

    277
    Oct 10, 2012
  4. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    The plate's not the issue. I put a dial indicator on it and it's moving less than 0.0005". Probably moving zero; my setup was quick and dirty. The plate I am using is a generic plate that I have machined to suit the GX7, including a light (0.020") cut at the back to clear the bottom of the LCD. (Having a 3-axis DRO precision milling machine in my shop is a very nice luxury!) The issue is unquestionably in the camera body somewhere. Best outcome would be loose screws but I am not optimistic and I don't want to go digging around in there unless I hear that others have GX7s that do not exhibit the problem.

    OT: Longer term I am going to use dual-clamp plates that work with both Manfrotto RC2 and Arca clamps. Using an Arca clamp on a monopod is problematic because you need one hand for the camera, one for the monopod, and one to tighten the clamp. The RC2 clamps latch when the plate is inserted, eliminating the need for a third hand.
     
  5. gr6825

    gr6825 Mu-43 Veteran

    277
    Oct 10, 2012
    OP - what part of the camera is moving? There may be multiple variables at play. You are talking about racking the lens to 140mm, so the double nested barrel is fully extended and probably has a bit of play. Do you have access to another GX7? That way you could compare to see if there is an issue with yours.
     
  6. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    Thank for your attempts to help via theory, but I am looking for someone with actual experience or who can check his/her GX7. Both my GX7s are the same.
     
  7. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    It is.
    9468114.

    Although you're very very lucky, making that assumption without checking, because most camera bodies at that price aren't metal at all.

    So, it's not what you think it is, so look elsewhere. Screws?

    I will try and remember to check it out tonight.
     
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  8. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    Thanks for the photo. The tripod socket is steel, so it won't actually be part of that casting but seeing the casting gives me hope. It would certainly be possible to positively attach the socket to the casting.

    There are plastic trim panels on the bottom of the camera. These are what the plate contacts. I think I could put a washer on the 1/4-20 screw and be sure that the plate was making positive contact with the steel, but a washer diameter is a pretty small support platform. I don't have time tonight but tomorrow I'll try pulling the panels and see if there is some reason there could be compliance there. Maybe I could shim underneath the panels or something. I might also try a washer as a quick test. I'll keep you posted.
     
  9. T N Args

    T N Args Agent Photocateur

    Dec 3, 2013
    Adelaide, Australia
    call me Arg
    Have you tried the same test with anything other than a GX7?
     
  10. gr6825

    gr6825 Mu-43 Veteran

    277
    Oct 10, 2012
    I hate to be a broken record, but a body plate (like the RRS unit linked above) is designed with your concerns in mind. It has multiple contact points with the camera body to ensure a snug fit. I used to use universal plates, but I found the dedicated units from RRS to provide better grip.
     
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  11. m4/3boy

    m4/3boy Mu-43 Veteran

    306
    Jul 21, 2013
    +1! To the OP if you get a base plate your problems will disappear.
     
  12. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    I can't replicate your experience with my GX7 and 14-140, but it seems I don't own a stiff, heavy enough tripod to allow the body to flex differentially from the tripod. I get a 1-to-1 movement of body and lens.
     
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  13. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    OK, problem is now better understood and solved adequately, but not perfectly.

    I tried what I mentioned last night, using a small washer to ensure solid contact between the steel tripod socket and the plate. Result was clear/surprising proof that the tripod socket is not well anchored in the camera body. I tried to take a trim plate off to see the connection, but there was more holding it than the four #000 Phillips screws that I removed, so I abandoned the effort.

    I then looked much more carefully at the camera bottom and found that the tripod socket was standing a tiny bit, maybe 0.003", proud of the camera base. Since my plate has no padding, this means that the plate was really not in contact with anything but the socket, even sans washer.

    So I counterbored the plate by 0.010" -- enough that the plate is now making contact across the whole bottom of the camera (50mm wide plate) and the tripod socket is not contacting the plate at all. With this fix, the stiffness of the assembly is substantially improved. It is not totally fixed, but the flex is now down at the same acceptable level as the very small changes that occur when the Acratech knobs are tightened. I can also still move the camera with zero changes by holding the Arca clamp and keeping my hands off the camera body completely.

    FWIW, the lens flange has the same poor anchoring problem as the tripod socket. Putting even small forces on the lens, either near the flange or the extended end, causes the image centering to change significantly. So, the lens is "hands-off" for framing. Too bad; it's the handiest thing to grab.

    Re expensive/different plates, the RRS, Markins, and Kirk plates are not counterbored (at least the pictures don't look like they are) so they would have the same issues as my unbored plate. Interestingly, the Acratech plates do have a counterbore so I think they would be solid right out of the box.

    Thanks all for the stimulating comments.
     
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  14. Cederic

    Cederic Mu-43 Veteran

    212
    Nov 14, 2012
    Nottingham
    Can I ask a naive and possibly stupid question? Why wouldn't you use a small rubber pad (or equivalent) to assure a broad and high friction contact between the plate and the camera? Although your tolerances are tremendous surely just adding that extra material would negate the need for such precision?
     
  15. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    There are no stupid questions. I have learned a lot on this forum, more often by making stupid statements and getting strafed than by asking stupid questions, but it's all the same. :)

    The stiffness I need is this: When I move the camera (pitch axis) to a particular position against the friction of the ball, then release my hold on the camera, I do not want the camera position to change. The issue I found was the tripod socket in the GX7 actually flexes under the minimal force needed to overcome even light ball friction. Hence, when I release the camera body, the position "rebounds" a bit up or down from where I set it. Using the whole bottom of the camera for plate contact and not relying on the socket for rigidity turns out to be my best, though not perfect, solution. That's the exact opposite of what I thought initially.

    Now if you think about introducing a compliant material between the plate and the camera base, then under pressure from vertical panning movement that material will compress a little bit and the camera will rebound when the pressure is released. The base of the GX7 is about 7/8". If I hypothesize that the flex and rebound front-to-back might be only 0.005" the resulting change in image center at 50 yards/50 meters is about a foot/30cm up or down. A sheet of paper is maybe 0.003" so you can see that 0.005" is not a lot of motion. So --- the last thing I want to do is to add compliance between the camera and the plate.

    If you look at the "pro" camera plates (RRS, Markins, Kirk, Acratech) I don't think you'll find a single one that has any compliant material between the plate and the camera body. They are all metal-to-metal contact. It is only the cheap plates that have the padding. That's probably why m4/3boy and gr6825 are so fond of pro-type plates; going from a cheap padded plate to an unpadded pro plate should make a real difference.

    As you suggest, the padding probably increases friction. And probably that is why it is there; to keep the plate from swiveling. The "pro" plates generally solve the rotation problem by adding a lip that is held against the front edge of the camera base, reducing the need for plate friction to prevent rotation.

    Most of the above is stuff I learned while studying this problem over the past couple of days. I just never had a "need-to-know" until my expensive Acratech ball head failed to solve my camera stability problem.
     
    Last edited: Jun 20, 2015
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  16. Listener

    Listener Mu-43 Regular

    oldracer, thanks for starting this thread. I use a Panasonic G6 body and Oly 60mm lens on a tripod for most (90%) of my pictures and have had no trouble. Your exploration has added to my knowledge and I'm happy to learn.
     
  17. Cederic

    Cederic Mu-43 Veteran

    212
    Nov 14, 2012
    Nottingham
    As I promised, a naive question :) Thank you for the thorough answer.