Handholding Vibration

This section presents some analysis of measurement data published by Charlie Kim in conjunction with Markins tripod manufactures in the USA and subsequently posted on a photography forum.

The paper is not clear as to the measurement method, but it seems likely these are measured using precision capacitive gap sensor or a laser vibrometer and probably indicate the rotational mode in one plane at an mount arm length of ~40cm, no sample rate or sample dwell time is specified.

The handheld data (page 4 of the report) is from two individuals labelled "Best Case" and "Worst Case" in this short note. Both data sets seem to be derived from the individuals firing a handheld Leica R6.2 including mirror motion, no indication is given to the number of frames fired but it may just be a single frame.

The data was captured from the printed graphs by non-uniform time sampling of the characteristics of the waveforms followed by cubic interpolation with a uniform 1ms sample interval. This is reproduced below.

The power spectral density of these waveforms exhibits a 1/F characteristic between about 10-100Hz.

Looking at the statistical variation during exposure length sections of each waveform yields the following plots.

So both the peak and RMS variation during the exposure period varies fairly closely to the 1/F rule as might be expected from the spectral analysis.

The mean and standard deviation are approximately the same until the shutter speed falls below 1/30, after which the standard deviation about the mean reduces relative to the mean value. This is because significant sections of dominate periodic sections of the waveforms are now being included.

So for shutter speeds above 1/30 the amount of movement between shots can be expected to vary more than below 1/30 although of course the absolute amount of displacement is less at higher shutter speeds.

This justifies the assumption the displacement is proportional to the shutter speed.

However this is only for the rotational mode, the source document does not provide any information for the common or linear mode.

To get an impression of how sensitive different focal length lenses are to the 1/F rule the following plots present the same information but divided by the shutter speed to indicate the sensitivity of the lens to vibration due to angle of view.

This shows that with poor technique the 1/F rule is a good guide to relative handholdability. However, a user with good technique has more advantage with shorter focal lengths, or conversely it is more difficulty to suppress the effects of handholding vibration at longer focal lengths by using technique.

This again illustrates the value of IS at longer focal lengths.

Last Updated 05/06/2008

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