5
One also has to take into account tangential velocity (rotational speed).
The further away the rotating point is from the center axis, the faster
the tangential velocity and the worse the blur appears to be – it is
always the same number of degrees of rotation but the physical length
of the blur gets bigger as the point moves faster. The strobe adjusts the
width of the pulse automatically to keep the degree of rotation visible
constant.
There are two methods of adjusting the flash pulse width, and hence
the brightness and consequently the blur.
4.2 Degree of Rotation Adjustment
The first method is to adjust the flash pulse width for degree of rotation
visible (blur). The user can set this from 0.2 to 14 degrees out of 360.
The higher the setting the brighter the strobe appears to be but the
target is more blurred. Optimal setting to stop motion is 1.8 to 3.6°.
The number of degrees is a proportional amount and remains constant
as the flash rate increases or decreases. The strobe automatically
calculates how wide the pulse width should be at different flash rates
to keep the blur constant – the faster the flash rate the narrower the
pulse width. The pulse width equals: (setting in degrees/360) x (1/flash
rate in Hz).
Thus the blur remains constant no matter what the flash rate*.
4.3 Pulse Duration Adjustment
The second method is to adjust the flash pulse width to a fixed
number of microseconds. Here the user sets the flash pulse width in
microseconds not degrees. As the flash rate increases the pulse width
stays the same and the image will get brighter and more blurred as the
flash width remains constant*. The degree of rotation visible changes
to keep the pulse width of the flash constant*.
