The question that I would have is "Does the difference in the crop factor make any difference?". The 1d2 has a 1.3 crop factor whereas the 5d is FF
This wouldn't be a problem as the ball is a constant size so if the OP has measured the distance using the diameter of the ball then this would be the same for each picture as the ball is a standard size.
Correct, the ball is 6.7cms and I am going off the ratios of width of the ball vs. length of the blur.
I did take 3-4 shots each, and these are the longest "blurs" for each bowler. The bowler's had relatively consistent blurs in the 3 shots I took.
There is some movement in shot #1 but it is more vertical (look at the blur of the ball, there a slight hump); without that movement, the ball would have been even faster, so that's not what is causing my 15% difference.
Goes back to the accuracy of the shutter speed. I was googling "shutter speed accuracy" and came about some experiments people did at 1/100th of a sec and found after 75 shots, the shutter was languishing at 1/140 -1/160th of a second... sadly I forget what camera it was.
So does anyone know if Canon shutter speeds are accurate or does +/- 15% fall under an "acceptable tolerance" ?