I would like to know if a camera tripod (let's say not the biggest one, 40-50 cm folded) can be taken on board inside hand luggage, or it has to be put into the aircraft hold?
Is there any problem for camera (DSLR) and lenses as well?
If it is within the airline's dimension for a carry-on, then yes.
Note however, they might legitimately count it as one carry-on toward your allowance.
Also, whoever is staffing the terminal entrance may do an extra check.
Any camera should be no problem. I would never check a camera.