VR advice please

Started May 7, 2012 | Discussions thread
pocketfulladoubles
Senior MemberPosts: 1,986
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Re: elaboration please
In reply to John M Roberts, May 9, 2012

A tripod and a human obviously work very differently. The human has the ability to impede some of the motion by for example, softening ones knees to reduce the motion. The human can do this for very low frequency, up to a point.

A tripod is essentially fixed to the bridge, and will have a response spectra at the top of it. At these low frequencies, it would typically appear "stiff" and you basically get out what you put in. At higher frequencies you will get some resonance, depending on the damping in the system, and at very high frequencies (above resonance) they will again drop off. The motion at the top of the tripod would excite the cantilever which is the body/lens system and head coupling. That has its own frequency response based on what is present at the top of the tripod, and you are correct that it could undergo amplification at a totally different frequency.

The biggest factor to consider is that rotation is a much bigger evil than translation. Why? The total displacement is small potatoes compared to the arc of motion that is swung by rotation in the lens cantilever. For this reason, it is typically a very stiff tripod and head combination, and locating the lens/body system over its rotation node that will reduce the problem the most.

John M Roberts wrote:

Bob GB wrote:

On a tripod the mass of the camera and lens together with the stiffness of the tripod head makes a vibration system with a resonance frequency at which this system will vibrate if excited in any way. If the camera/lens mass is smaller the resonance frequency is higher. If this resonance is above what the VR system can handle it will not work properly.

In your case the frequency of the bridge is far below any problem frequency for the VR system. However, the vibration on top of the tripod is not effected and is (probably) still above what the VR system can handle.

I'm a bit confused by your explanation. "However, the vibration on top of the tripod..." vibration coming from the bridge? Do you mean the top of the tripod is not affected by the vibration from the bridge in the same manner as is when handheld? I can imagine that it would transfer to a different frequency.

What you can do is putting your hand on the lens or camera and thus dampens any possible high frequency vibrations caused by the tripod. Instead your hand will add low frequency movements but still much less than if you are handholding the camera.

By doing so then the VR would be able to help or would that make the overall setup too solid to apply VR? Unfortunately I do not have a similar scenario to duplicate to test presently.

Thanks for the breakdown.

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