EFCS controlling External Vibration?

[austrokiwi1]

First off I feel silly asking this question. Silly for two reasons:

1. My current understanding is correct and therefore I shouldn't doubt myself, or
2. My current level ofunderstanding is hopelessly wrong.


In another forum I mentioned I had modified my rig by replacing the base plate of my copy stand with a 29 Kg granite slab and sitting it on sorbothane feet. Now I did all this to control external vibration.

An old hand in that forum then commented that if a camera has EFCS then that modification wasn't necessary. I understand EFCS controls for shutter shock( depending on how good the system is) However I just can't get my head around the idea that it can control for external vibration?

I am hopelessly wrong?

[ChrisR]

No, not wrong at all.
Where's the other forum, it's moderately likely that the other guy meant something different?

Obviously you don't want things moving about on the camera itself.
If the camera DOES move, then if it's rigidly (enough) connected to the subject, then no matter. But experience and tests show it does matter, so the vibrations must be relative, between the two, because you do see shutter-induced movement if you look for it. Hence EFSC is a good thing.

The main remaining source of trouble is the environment, let's say the floor. Vibrations have a hard time getting through the Sorbothane because it tends to absorb energy and not transmit it. The energy that DOES get through, has a hard time moving (vibrating) your granite very much, because it's massive. (f=ma, large m, low a).
Then the granite is also quite good at absorbing high frequency energy, unlike say ball bearings. You can't make a bell out of granite.

Without the Sorbothane and the granite, a spectrum of vibrations would get to your sensor and subject through the floor, and they'd react differently to them. And you'd see the difference as blur.

One theory goes that if you can make your sensor and subject be sufficiently rigidly connected together below a frequency F, and then prevent higher frequencies, you get no blur. So you make sure your floor route cannot pass any frequency higher than F. Which works, with a few ifs and buts.

I suspect there's nothing new to you here, and it's mostly right.

[austrokiwi1]

Thanks... you have given me more information that suggests something I did by instinct( or remembering how to set up a hi fi system) was a good idea. Prior to getting the granite I had been using a 400mm X 400mm X30 mm concrete paver to add weight to my rig. Of course it was redundant once the granite was in place...I went and bought a second concrete paver and now the bench style table my rig sits on has two 15kg concrete pedestals to sit on. From what you've said that will help reduce some vibration frequencies