VR advice please

Started May 7, 2012 | Discussions thread
pocketfulladoubles
Senior MemberPosts: 1,986
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Re: Some more thoughts
In reply to Bob GB, May 10, 2012

Bob GB wrote:

Nikon has never published any technical details about max frequency and so on. And frankly, I do understand they haven’t because how should you know the frequency of vibrations. In addition it would probably create a lot of frustration.

I think you can still use a tripod but act to remove all high frequency vibration by damping or absorbing them in some way. Using the hands on the camera would be one solution.

Take that same setup but on a floating device in a river such as a dock or rowboat, the movement is entirely different. I would suspect dampening the camera atop the tripod would not be necessary unless there was an engine attached and running.

Yes, you need to remove high frequency vibration because they can occur as long as you utilize a tripod. Even on bedrock the wind blowing can cause vibration in the tripod.

Low, mid, and high frequency is really going to be relative to the fundamental frequencies of the angular vibration. Let's call "low" the region below resonance. Vibration there is reduced with additional stiffness in the system (good tripod and head). For the "mid" range, say at and around resonance, one would apply damping (usually the more challenging measure, but sometimes just touching the system lightly with the hand will work). And for "high", the region beyond resonance, assuming it is not SO high that the system has broken up into higher order modes (i.e., transmission line behavior), one would reduce the motion by adding mass (the old sandbag hanging from the center column trick). For this reason, we usually refer to the relative frequency regions as stiffness, damping, or mass controlled regions.

Since we are dealing with the rate of time (shutter speed), we care about the vibration velocity response. In other words, how much motion will be traveled in a given amount of time. Recall that integrating in the frequency domain (real component) is a divide by frequency. So, as you move to higher frequencies, you will find that the velocity gets smaller and smaller, assuming random signals. Therefore, very high frequencies won't matter so much. What we still care about are the regions near resonance.

There are too many variables to estimate the resonance region of a given in a camera system, and there are too many different sources of potential vibration. It would be nice if Nikon did release the impedance curves for the VR system, because there are times (in labs) when we can deal with the parameters. Based on my experience in modal testing, this would take an engineer about a day to complete, per lens, meaning you are taking a high level engineer out of work for a month or two to give curves that only a small handful of people would use. Is it worth it? Probably not. Those that really would benefit from this could run those tests themselves, or hire someone to do so. The rest will take pictures and gain the knowledge through experience which is far more valuable in any uncontrolled circumstance, like standing on a bridge, anyway.

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