David Mann wrote:
On Dec 20, 2005, at 8:21 AM, Ronald Arvidsson wrote:
I've at times thought to use seismometers to measure the vibratins
from different cameras - being a seismologist.
The measurements are in time domain - i.e. one measure during the time
before at and after exposure. It would be necessary to use recording
equipment that is utilizedin mines (for control of mine shocks) which
have high enough time resolution. In this way one could possibly record
tripping of shutter, mirror movements and stop, shutter opening and
closing. There is still a problem of translatingthe actual ground
motions to the motions at the camera. Still the frequency of ringing
would be recorded and how fast this would be damped out. A possibly
better setup would be to use a high speed camera, such as being used
when recording bullets moving in the air.
That's an interesting idea but I'm not sure if it'd be very
accurate. For an accurate measurement of the vibration that actually
affects the image you'd have to only measure the vibration while the
shutter is open.
These instruments can measure the exact frequencies of the
vibrations and one could have a deterministic measured value and not
just guesses which are based on how solid/loosely camrea is fixed to
tripod or hand. Maybe I'll make a test within the next few weeks of
this?
It'd also depend on the tripod itself. I've heard that wooden
tripods are far superior because they actually damp the vibrations,
where metal legs will just ring at their resonant frequency.
Sure, the whole setup, camera tripod has its own eigenfrequency
combination and damping. If the eigenfrequency of camera is very
different from tripod these to movements should counteract, if similar
they will amplify the movements.
Cheers,
Ronald
- Dave
