ghiblipg:
Actually how do i know how much weight a motor can support?
For example, a normal high end DSLR + lens would be around 1.5kg.
How to relate the motor spec with this weight?
Depends on how you build your rotating platform. If the platform is well designed with good bearings and no holding load on the servo, a very small servo could rotate it. You need to do some research in the mechanical design area for your device.