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  1. #1
    rmolson's Avatar
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    vibrations and mass

    Vibration and mass

    I have been running film developer tests with FP-4 in Rodinal and D-76 in my Bronica and TriX in HC-110 with my 4x5 Bush with a great 150mm Topcor lens. Trying to get something closer to Barry Thornton’s sharpness. In both cases I have been getting less than spectacular results..The images are just not that sharp Which has been something of a mystery as I use to get very good sharpness with the same combinations and even an old beater 135mm Raptar lens and my old Yashica D TLR! Today checking for focus shift, on the Bush indoors It is way too windy outside, I was slightly spooked when I watch the image dance on the ground glass as I focused. The camera was mounted on my new Slik Universal 212 Deluxe, rated to hold 15 pounds! I decided a few months ago to bite the bullet and get really “good” tripod and pay the big bucks At first I thought it was the tripod mount, a very sexy screw in device attached to the camera and then inserted into the tripod pan head and locked down, Much more convenient than lining up a the mounting hole while holding the camera and turning the set screw on the pan head. Great tripod about 2 to3 pounds lighter than my old 30 plus years all metal Slik with knuckle busting knurled ring locks on the legs. But when in desperation I got it out and mounted the camera ,the vibrations ceased! I should have picked up on this before when I was shooting with a 400mm on my OM1 this summer using the new Slik. The sharpest results came not from the mirror up and cable release, but by placing my left hand on the top of the lens ( On its on tripod mount ) and bearing down while tripping the shutter with my right hand. In my working life I was a graphic arts cameraman not an engineer. But I remember high school physics 101 and Mass. The newer lightweight tripods while stronger than the old aluminum ones have less mass, and mass is what dampens out vibration.
    I can hang some weights in a camera bag over the camera to compensate but this sort of nullifies the whole idea of lightening the load for field work
    That is unless some one has a better idea.

  2. #2
    David A. Goldfarb's Avatar
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    Using a hand to dampen the vibrations with a long lens is a fairly well established practice among nature photographers. You have to test and see if it works with your equipment and technique, but it often does. That's a bit of a different situation than when using a press camera, because you have shutter vibrations traveling down the lens and becoming magnified in some cases.

    I had a Slik U212 for many years--a very versatile tripod, but the head and quick release systems aren't really the strongest things out there.

    Sometimes a tripod may just have a resonant frequency that is sympathetic to the vibration of the camera, and it doesn't matter how big a tripod it is--it will vibrate.
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  3. #3
    wiltw's Avatar
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    Mass and resonance are two different things. The Seattle Tacoma bridge had plenty of mass, but wind induced vibrations at the resonant frequency brought it down!

  4. #4

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    YOU GOT IT
    The point that most folks missed in the wood-vs-metal tripod discussion.....
    So if you can't carry a massy tripod, sit on the camera.
    But really, how about stepping into a stiff bungy cord that hangs from the bottom of the head- you carry that mass in your shoes in any case- the cord needs to be just stiff enough to not lift your foot off the ground when stretched to the dirt.

  5. #5
    keithwms's Avatar
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    The coupling between camera and tripod is the most overlooked source of vibration. The camera, and the tripod can any mass... and you'll still have vibrations if the coupling acts as a fulcrum! A tension line away from the fulcrum greatly reduces the vibration; for this reason I often tie the cable release to the tripod and that provides a bit of tension.
    "Only dead fish follow the stream"

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  6. #6
    Nicholas Lindan's Avatar
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    A good check for resonance is to place one hand softly on the camera and give the camera a rap with the other hand. If the camera feels like its a tuning fork they you have problems.

    It's not mass that damps vibration - though adding mass can lower the resonant frequency of the system enough so that it becomes functionally stable and the camera can not exert enough inertial slap to cause much of anything to move. Vibration is damped by friction or viscosity, and vibration damping is an art in itself.

    The best mass to add is mass that doesn't resonate - tying the camera to a brass bell isn't a good idea, tying it to a sack of cement is. It is common to place a sandbag on a camera or at the end of a long lens. Another technique is to eschew a tripod all together and place the camera on sandbags on a tree stump, wall or hillock. All sorts of things - socks, plastic bags, sheets of paper - can be drafted into emergency sandbag duty by filling them up with whatever is at hand.

    Lightweight tripods can be stabilized by hanging a sack of rocks from the bottom of the center column, some tripods have hooks just for this purpose. Another trick is to run a cord around the legs at mid level and tighten the cord - I think Berlbach tripods have this feature.
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  7. #7
    Lee L's Avatar
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    Quote Originally Posted by Nicholas Lindan View Post
    Lightweight tripods can be stabilized by hanging a sack of rocks from the bottom of the center column, some tripods have hooks just for this purpose. Another trick is to run a cord around the legs at mid level and tighten the cord - I think Berlbach tripods have this feature.
    My Berlebach 8043 has both the hole through the center column and the slots for a cord at the first leg joint. I've hung a full camping water bag from a cord wrapped around the legs of a metal Manfrotto tripod a couple of times.

    I recall a test published in one of the better magazines a decade or two ago that indicated that the real problem is system resonance, the resonant frequency of the whole camera/lens/tripod system. Some combinations were excited at higher shutter speeds, and not at slower speeds. You also see reports that wooden tripods dampen resonances more quickly than metal. My metal and wooden guitar bodies both resonate nicely, so I'd say it likely depends on the structure of each tripod.

    The main thing is to test and see what your system is giving you.

    Lee

  8. #8

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    Quote Originally Posted by rmolson View Post
    ... mass is what dampens out vibration.
    Nope. Vibration is a bit more complicated than that. A good rule-of-thumb is that increasing mass tends to decrease natural frequency -- depending on the system of course. And this may or may not be what you want to happen.

    There are many ways to control vibration. Adding mass isn't necessarily the smart thing to do, certainly not in all cases. Just sayin'.
    Bruce Watson
    AchromaticArts.com

  9. #9
    keithwms's Avatar
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    Again, the tripod mount usually acts as a fulcrum, about which the camera can pivot and oscillate. Most people have the intuition to try to balance the camera's weight on there... but that actually makes it easier for the system to oscillate. What you want to do is break the symmetry of the mode. That will spread the Q factor and then it will damp out very quickly. So tie a string or use the cable release as I just suggested.
    "Only dead fish follow the stream"

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  10. #10

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    Quote Originally Posted by keithwms View Post
    Again, the tripod mount usually acts as a fulcrum, about which the camera can pivot and oscillate. Most people have the intuition to try to balance the camera's weight on there... but that actually makes it easier for the system to oscillate. What you want to do is break the symmetry of the mode. That will spread the Q factor and then it will damp out very quickly. So tie a string or use the cable release as I just suggested.
    Lowering the center of mass by using a stiff bungee cord to hang a heavy pack from the bottom of the center column is worth trying. I use either a wooden tripod or a heavy Linhof studio tripod (transportable by car and a short walk). In both cases I have rubber and cork gaskets to help dampen contacts between camera and tripod head, tripod head and center column, column and tripod. Placing a hand on the lens while using a cable release is something that's worked as well. In the end this is an empirical problem so try the various suggestions here and in previous posts above and take notes to help evaluate the final results.

    RT
    "Get over it."

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