is there a thumbrule for shutterspeed and motion blur ?

I just did a rendering on 24fps and default motion blur setting, and the clock shape shutter.

It looked a bit weird, like small shocks, i now the effect is gone when i use a higher frame-rate.
But then i was thinking of my own camera a canon 60D with magic lantern.
There i never get that small shocking effect; somehow then things get more blurred.
even if i set the shutterspeed to manual (can be done with magic lantern firmware on the canon).

So i was wondering is there some kind of thumb rule to keep in mind so that that animations look nicely smooth on blender.

What is a clock shape shutter?

Historically, shutter angle was usually 180 degrees (0.5 on scale 0-1) which gives shutter time of half the frame duration. For 24fps it is 1/48th second, for 25 1/50th of second and so on. The smaller the shutter angle, the sharper the image, but it also introduces the stutter.

the clock shaped shutter, is the new modi of an emulated shutter in 2.77
Ah yes that 180 degree rule i remember now, thats been a while ago… wow.
Kinda strange this isnt automaticly set most people never had that deep camera training.
Hm going to experiment more on this, i’m not sure yet if it all will match up.

Experimenting again, checking realism of blur.
I looked up the shutter time as defined on blender wiki :
ShutterTime (in frames) the shutter is open. If you are rendering at 24 fps, and the Shutter is set to 0.5, the time in between frames is 41.67 ms, so the shutter is open for half that, 20.83 ms.

That is rater strange as with 180 rule it should be 1/48 typed in the field there… i dont see any blurring effect then

The shutter field expects not time value but shutter angle in range 0.0-1.0 where 0 is 0 degrees and 1 is 360 degrees. So 180 degree shutter is 0.5 and for 24 fps it gives shutter open time 1/48th second which is this 20.83ms.