Simar,Oks. Thanks for the info.
Narrower then f/5.6 bookeh will be effected isnt it, will not be so much creamier.
I think i should have pumped ISO so as to get desired exposure.
In this type of light, in a party hall say as shown in image, what should be the exposure so as to get perfect sharp images?
Ankur has said it but I will say again. The shutter speed was too less for the action shot you taken.
The rule of thumb is such 'The minimum shutter speed to shoot sharp pictures (without motion blur) should be the reciprocal of the focal length'. This is for 35mm format, so in your case APS-c format multiply by 1.5.
So now you shot with 50mm, so the min. shutter speed should be 50x1.5=75mm.
Now, this rule of thumb holds true only if you are shooting static subject. When shooting action/motion shot the shutter speed will depend on the type of motion. Faster the motion, faster the shutter speed. How much? This you can only know by practice.
OS/VR-Vibration Reduction helps in giving sharp picturesr with slower shutter speed than this rule of thumb, but only for still subjects. VR does not help much for action shots.