Cokin Adaptor Ring
Adaptor rings allow to attach the filter-holder on the lens. First, check if your lens has a thread to be able to screw the adaptor ring on it. Then, find the filter diameter of your lens. Most of the time, it is written on the front of the lens itself. If not, check the lens user manual. Finally, just screw the ring on the front thread of your lens, and you’re done! If you have lenses of different diameters, you only have to change the adaptor ring. It’s very economical!
Choosing the right system
Adaptor-rings are the first step in determining the system you should use. They are available in various diameters. First, refer to the lens with the biggest diameter you own. The diameter of a lens is either written on the front or side of the lens itself, in the cap, or in the lens user’s manual. Once you know what is the diameter of your lens, chose the system that will fit your needs.