What is the maximum weight of a lens you can put on Sony PMW-F3? I see that some people use rails which provide additional support for lenses. I don't have such rails and I wonder if its ok to put a lens like Nikon 24-70 on this camera without any support? Thanks.
If weight information is published by Sony then it would be in the manual.
But a 24-70mm is fine. Many use rails for the client impression they provide, and also for other accessories like follow-focus systems. Most of the time a lens support is used for mental appeasement.
The Sony FZ mount found on the F3, F5 and F55 is very strong, no worries, especially with a DSLR lens. If you are using Nikon, you should really get the Optitek Nikon prolock adapter, which gives you cinevised iris for all Nikon glass.