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ABOUT TRIPOD, HEAD AND VIBRATION

MARCH 2005

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hear the sound generated by the shutter driven at full speed at Dpreview website.33

If you want something really sturdy, then look at the result here with the same Nikon D2H test with Markins M10 and ‘Linhof Heavy Duty Two-Section Pro Tripod’.34 The weight of tripod itself is 16.oolb (7.26kg).

Tripod also played a role here. Tripod legs were not pulled out in both cases. So the only suspect that caused this difference is the material of each tripod. Assume you have long cylindrical rods, one in wood and the other in crystal, with same diameter and length. Now hit one end of each rod. The sound generated will be quite dif- ferent. Energy propagates more easily in homo- geneous material. From this ground, we can ex- pect more dampening in carbon fiber material.

We can suspect one more reason. Because there is a gyro-force acting on the ball head caused by the motor drive FOBA tends to slip away from fixed position. It can stand static force but fails to hold its position if dynamic force such as impact is given. This is also a clue why we need very large load capacity in ball head.

You can see the very detail by zooming in this pdf document. Close examination will tell you how the slips in micro range affect the vibrations. Signal pattern in Markins M10 is very consistent while FOBA pattern contains very low frequency drift under 1Hz. This low frequency vibration is due to an insufficient holding force in presence of high frequency impact load. 32 You can also

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torque). Forcing it slowly or hitting with soft material is not enough. A high frequency impact load makes it easy to pull out the bolt. This applies exactly the op- posite way in tripod ball head case.

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32 Assume a tightly fixed bolt or screw, to unscrew it one usually apply an impulsive load (to be specific,

34 http://www.dpreview.com/reviews/nikond2h/page6. asp http://linhof.com

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The result is also something that cannot be reached by a portable(!) tripod.

Loose Assembly: Just Not Good

Auto focus lens is convenient but not without sacrifices. You can easily locate badly designed AF lenses. For less power consumption and fast tracking speed, they give up the quality of tight- ness. If your lens shows a lot of playing among parts, it will never know where to put the donuts. If you want more information see the article by Robert Monaghan in Medium format library.35

AF lens is more apt to vibrate than MF lens.

This is an example using Sigma SD9 with standard zoom lens.

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I bought this camera with the cheapest lens be- cause of limited budget when we need a digital camera for work. I was also curious about the Foveon X3 sensor. It’s true that it generates less Moire patterns36 but it becomes worthless with a bad lens construction. It becomes like the above even with Gitzo 1227 tripod and Markins M20 ball head. Every part in zoom lens plays ar- bitrary colliding with nearby parts. I’m not saying that the entire lenses from Sigma are bad. The

35 36

http://medfmt.8k.com/third/af.html http://www.mathematik.com/Moire/

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