Chuck Norcutt wrote:
> Now here's a subject for some real world experimentation. I don't have
> any bean bags but I remember Walt's comment on the subject and I'm
> pretty sure he said he uses lead shot. (What else from Walt, eh?)
>
> I thought, that's gotta be the best because it has the most mass. But
> maybe it's not. Maybe a 1 pound bag of dried peas is better. Or, maybe
> it's not more better than lead shot but still plenty good enough. Maybe
> my 18 lb. light stand sand bags would work well if they didn't crush the
> camera and tripod.
>
I've got this theory that it is a combination of total mass, number/size
of particles and friction between particles.
Total mass is basic Newtonian physics. The greater the mass, the less it
is affected by any given stimulus. However, if it is rigid, it may have
sympathetic vibration modes.
Beyond simple mass, I think much vibration is absorbed in friction
between particles as the waves are transmitted between particles. So you
want enough friction to use up energy, and not enough to lock up the
connection and transmit the energy without loss.
So effectiveness would be affected by the size, mass, shape and surface
characteristics of the particles. Another important factor is coupling
to the camera/lens. There has to be enough weight and contact area for
the bag to absorb the vibration. With lighter, bigger particles, the
fabric of the bag could become a factor in how it transmits vibration.
If it's slippery and the weight is low, the vibration could simply slide
against it, without going through to the filling.
> Has anyone ever done any experiments?
I've done thought experiments. :-) Styrofoam balls would be very poor -
low mass, few transmission points and those "sticky" so minimal friction
loss. I'd guess, for example that lentils would be better than dried
peas. Smooth enough to move easily against each other, but relatively
denser, so there is more force across each transmission point, meaning
more friction loss, and smaller size, so there are many more
transmission/absorbtion locales. I'd expect smaller lead shot to work
better than large. Also sould seem likely to couple to the camera/lens
better.
Same thing with beans, adzukis probably better than pintos.
Sand is an interesting one. Source material, shape and surface
characteristics might lead to very different results for different
kinds. With very irregular, sharp edged shapes, it might tend to lock up
and transmit vibration relatively unaffected. I know there are certain
beaches which seem to almost amplify the sound of impacts on them.
Relatively larger, well worn to smooth edges sand might work rather well.
My bet for a winner is on bird shot.
A. speculatin' Moose
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