Higher frequency, large amplitude vibrations are going to tend to create higher accelerations. And within reason, higher frequencies are going to be a bigger contributor to higher accelerations as opposed to increased amplitudes, but IS is going to respond better to larger amplitude changes only if the frequency is high enough to produce a detectable acceleration. That was a very confusing, and loaded sentence... better said, it is the accelerations that create the forces needed to measure vibrations... and that goes for IS systems as well. With a building there a couple of different vibration modes - 1) those induced by the buildings equipment (motors, elevators, HVAC, roof mounted equipment, etc.) which tend to be higher frequency and lower amplitude; and 2) the sway of the building due to environmental inputs (wind, thermal expansion of sunny side vs the other side, etc.) which tend to be higher amplitude and very low frequency. The sway of the building can have some rather large amplitudes, but the frequency is very low and is not likely to be seen by IS (unless there is some higher frequency torsional component). However, I would say that the man made/induced vibrations from mechanical systems would be something that the IS would handle.
Back when I was in college (pre-invention of the wheel, but dirt was invented that year) we had a 12 story Mechanical Engineering building. Being the nerds we were, we put some accelerometers on the upper floor and a few of us would run back and forth to get it swaying... then measure the acceleration and calculated the displacement. I was really surprised how much it moved. I do not remember the number, but it was in the inches. And others had measured in high winds and found the displacement to be quite high. If you were on the 24th floor in any kind of wind, I would think you would have problems with blur, but only if you were shooting perpendicular to the direction of the wind or if the wind set up some torsional motion (which does not seem good for a building).
There... my nerd fix for the day.
Pat
Originally Posted by conropl
Higher frequency, large amplitude vibrations are going to tend to create higher accelerations. And within reason, higher frequencies are going to be a bigger contributor to higher accelerations as opposed to increased amplitudes, but IS is going to respond better to larger amplitude changes only if the frequency is high enough to produce a detectable acceleration. That was a very confusing, and loaded sentence... better said, it is the accelerations that create the forces needed to measure vibrations... and that goes for IS systems as well. With a building there a couple of different vibration modes - 1) those induced by the buildings equipment (motors, elevators, HVAC, roof mounted equipment, etc.) which tend to be higher frequency and lower amplitude; and 2) the sway of the building due to environmental inputs (wind, thermal expansion of sunny side vs the other side, etc.) which tend to be higher amplitude and very low frequency. The sway of the building can have some rather large amplitudes, but the frequency is very low and is not likely to be seen by IS (unless there is some higher frequency torsional component). However, I would say that the man made/induced vibrations from mechanical systems would be something that the IS would handle.
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