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MARCH 2005

stand the situation. I upgraded my spell casting words from previous version.

“Locomotor mortis!” or “Petrificus Totalis!"15

External: wind, wave, ground vibration, etc.

Internal: mirror shock, shutter vibration, user vi- bration.

Vibration: how much?

Amplitude: minimum under 3um in amplitude. Normally it can be under 20um. Even with some care, it is easy to be more than 300um.

Frequency: frequency range of the resulting vi- bration depends on the length and design of the camera system. Typically it ranges from 20~100Hz.

Vibration: look like what?

Rotational mode of vibration is dominant. It means that when one end of lens goes down, the film side across the tripod goes up.

Vibration: measuring equipment?

All that's listed and shown became a single stone including the floor16 except the camera. I think that you need this spell in very windy field. This is the ideal vibration-free camera support setup. If I remembered it right, Ansel Adams was carrying a big solid concrete block to make the support stable.17 Precision machine tools always sit on top of the big solid epoxy granite bed.

Vibration: from where?

One needs to have very good and expensive setup to measure and record vibrations from the camera. I used a precision capacitive gap sen- sor and a laser vibrometer with an analog to dig- ital converter board and sometimes with a spec- trum analyzer.

Vibration: basics Here is the most basic equation in vibration.18 F = m x"+ c x'+ k x

15 http://www.bellaonline.com/articles/art11045.asp http://gothlupin.tripod.com/s.html

16 In fact, the building also vibrates but we are not going to consider that. A giant step of a heavy guy can make the floor vibrate about 5um.

17 As I’m searching for a reference, I encountered something similar recommendation at other site. http://www.popphoto.com/idealbb/view.asp?topicI D=34882 “With any 500MM lens, proper shooting technique is not optional--it's required. Sturdy tripod is Numero Uno. If possible, use a 20 ton block of solid concrete.”

The camera-tripod system is assembled with many parts including even the ground it stands. Every part interacts with each other. What is transferred is a dynamic energy. This energy can have different forms such as deformation, acce- leration. Whatever the form is, the amount is equal. With lots of simplification, we can finally

18 I used " mark as a double derivatives, so x" means acceleration, x' means velocity so as not to include symbolic font in this document.

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model the system with this equation. F = m x" = m a Fsystem1 = Fsystem2 m1 a1 = m2 a2 = Fequivalent

So if one of the mass is big then its acceleration and the resulting vibration will be smaller.

Vibration: of which system?

The last equation is very simple. With given mirror or shutter mass, we can have smaller response when the mass of the other side of equation is big. Is using heavier camera and tripod setup the only solution? There is more.

Vibration: rigid or flexible?

The virtual setup assumed to be made of stone might be the most stable setup. Heavier tripod might be the next practical alternative. On the contrary, if your camera is suspended from a single wire, this will be the minimum mass you can get. Real world lies in between these two ideal situations.

There is a possibility of having heavier system if you can add mass effectively. You can do it by tightly and rigidly adding parts. Loose linkage along the vibration path will end this possibility.

Some of the plastic camera body and cheap AF lens are loosely assembled. It is inevitable to save battery power and keep the AF speed. Vi- brations are reflected and added at these loosely assembled contacts, which makes any effort to reduce vibration useless.

More Equivalent Mass: How?

You can increase the total equivalent mass of the system by rigidly attaching each part from a filter on lens to the ground on which the tripod stands. If any part along the system fails to pro-

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