QUOTE(amduser @ May 3 2012, 10:28 AM)
dont rely on post process la, get it right in the shot is more important

this is that kind of panning i wanted to make, but sometime my zoom lens cant track the subject well with AF-C because it is a crop lens and AF is slow

hard to hold zoom lens steady without monopod especially after running around the area for different angle
Doesn't matter, people still do with kit lens anyway. I'm using Tamron lens, and the AF is also slow and not all the shot will be good, there will be many fail shot.
You need to test with different shutter speed to see which match the best with the object speed. For GRA/autocross/autokhana, the speed can vary a lot and also depends, cause GRA involves more turning, so you need to also shoot at the right place..
QUOTE(Agito666 @ May 3 2012, 10:34 AM)
another question:
how fast shutter speed for make the car stopped?
how slow the shutter speed to make eveything blur?

If you use fast shutter, everything is FROZEN.
E.g. The tyre is not spinning (try shooting spinning fan, is your shutter speed is fast, the fan is frozen in your photo)
The background doesn't have the effect like the panning photo.
Panning means, your camera is moving tracking the subject. So, in slow shutter and you move your camera, what happens?
So how come the subject is not blur? Because you're FOLLOWING the subject.
It's best if you try it out, you can even pan people walking, or cars on the street, etc. Can even do with mobile phones.
One you're done trying it, with Flash, you can do much more, like rear-sync. Saw Initial-D effect, the cars leavin the trails of their back/brake light?