[robski]

Another way of looking at the problem.

In this example let us assume the camera shake causes a 1mm vertical movement of image on the sensor which will be true for both full frame and APS-C sensor. In the case of full frame this movement equates to 4.1% of the frame and 6.6% for APS-C. It is only when you use different scaling to make the same size print from each system the shake becomes more apparent.

If you use the same size area of the sensor in each case and apply the same amount of scaling the shake will appear the same.

Remember 1/focal length Sec is only a general rule of thumb (guide) which works for most people.

I am of the opinion that as you get older you are less able to hold the camera still at low shutter speeds. I find the IS on my 300 F4 a boom for hand held shots but not as good as tripod.