vibrations and mass

[rmolson]

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.

 

[David A. Goldfarb]

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.

 

[wiltw]

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!

 

[eworkman]

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.

 

[keithwms]

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.

 

[Nicholas Lindan]

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.

 

[Lee L]

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

 

[Bruce Watson]

... 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'.

 

[keithwms]

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.

 

[rternbach]

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

 

[MattKing]

This would be a good thread to post a cross-reference to in the medium format (and maybe even 35mm) forum(s).

Matt

 

[Barry S]

That Slik tripod is probably not a great choice for a 4x5 despite their claimed weight rating. It's more suitable for a small SLR. Keep your eye on craigslist--you can frequently find inexpensive solid tripods. I got a heavy duty tripod with a nice head for $50.

 

[rternbach]

Avoid extending the center column too high above the tripod base and, also, try using a head and a tripod whose weight ratings are significantly greater (50% greater or more) than the required minimums for the equipment being used. The latter suggestion may be overkill but I have found it helps quite a bit.

RT

 

[lxdude]

A couple of things-are you extending the center column? That will have a strong effect on platform stability, and depending how much it is extended, might affect resonance. Second, I just looked at the specs on the Universal 212 Deluxe, and the stated maximum capacity is 5.5 pounds, not 15. Also, I really wouldn't call $130 the big bucks!

 

[rmolson]

resonance

Resonance


Wow thanks for the great advice. I do remember reading about resonance , “but never thought it would happen to me”smurk anyway tried the shot glass with water on the camera and it was readily apparent I need to allow at least 5 seconds after touching the camera for anything to let it settle down and this is indoors. I’ll have to check out my Bronicas too This really does explain why I haven’t been getting pictures with very good equipment as I was with old beater cameras At least I now know what to look for. Thanks again

 

[Lee L]

Resonance- tried the shot glass with water on the camera and it was readily apparent I need to allow at least 5 seconds after touching the camera for anything to let it settle down and this is indoors

This is also telling you about the behavior of water. Try bouncing a laser pointer off an attached filter or the front of the lens and watch the reflected laser beam on a wall several feet away. That will tell you more selectively what the camera is up to.

You can also make an 'artificial star' (google for a number of DIY ideas) and record the image on film at varying shutter speeds. Keep good notes. The report I mentioned earlier found that one slr camera/tripod setup had a bad resonance around a specific shutter speed, something like 1/15th being much worse than either faster or slower shutter speeds.

Lee

 

[Larry.Manuel]

Consider a wooden surveyor's tripod. They are fairly heavy [but that in itself is no advantage] and damp vibration really well. They are stiff, so oscillations tend to be small or [appear] not to start in the first place. Astronomers have been battling wobbles and vibration for 400 years. There are lessons to be had there. Summary: as stiff as possible and incorporate some elastic hysteresis. The latter is the quality of materials that cause them to absorb energy when strained.

http://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis

 

[rternbach]

Astronomers have been battling wobbles and vibration for 400 years. There are lessons to be had there. Summary: as stiff as possible and incorporate some elastic hysteresis. The latter is the quality of materials that cause them to absorb energy when strained.
http://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis

Lessons to be found in biology as well: e.g. damping vibrations transmitted to a glass micropipette resting against a cell membrane. Which takes me back to worries about truck traffic and neurophysiology. So, an obvious question is what's the traffic like nearby?

RT

 

[rmolson]

vibrations

I live on a residential street in a small town with very little or no truck traffic
I took some of the ideas and cut a 1/2 plank of soft pine an mounted the camera screw and then offset a 1/4 20nut for the tripod screw. The wood seems to absorb more of the vibration.But what surprised me Was I was set up testing on my dining room wood floor and tried the same thing on the living room padded carpet, and the vibrations seemed stronger! Who would have thunk!

 

[John Koehrer]

I live on a residential street in a small town with very little or no truck traffic
I took some of the ideas and cut a 1/2 plank of soft pine an mounted the camera screw and then offset a 1/4 20nut for the tripod screw. The wood seems to absorb more of the vibration.But what surprised me Was I was set up testing on my dining room wood floor and tried the same thing on the living room padded carpet, and the vibrations seemed stronger! Who would have thunk!

There's usually a padding beneath the carpet so it's bouncier.

 

[rternbach]

Maybe this is just too far removed but I am reminded of an antenna problem--change the position and experiment with the location etc. and you finally arrive at the best S/N ratio.Camera optics can be fun.
RT

 

[lenny]

I hear your pain. I shoot with an 8x10 and the bellows acts like a sail even in the slightest wind... This will be the first mention of it outside our beta testers, but we are releasing a new product that should help. For those of you with iPhones, we are releasing an application that has a movement sensor in it. You just set the iPhone on the camera and if there is too much vibration it lets you know.... It has a sensitivity slider so you can set it to your own specs. It has a little database for keeping track of your shots with all sorts of things, a bit to help you with the zone system, etc. Should be in about 3 weeks....

Lenny

Lenny Eiger
EigerStudios

 

[Besk]

In my experience the contact between the camera and tripod support makes a huge difference.
You want to make the area of contact as large as possible. I don't like cork and I don't like metal.

I use a Busch Pressman myself but found that the little circular base of the camera was too small and could not be tightened enough with a tripod head with a cork or rubber pad. I replaced the small round base with a large 1/4 inch aluminum plate cut 2 1/2 by 2 3/8 inches. This gives me a much firmer connection with the tripod head.