The Cokin filter system utilises a filter holder that connects to your SLR lens via the filter thread. The holder is then able to take whichever filter(s) you require to obtain your desired result. Approx 200 filters are currently available ranging from the basic UV to many special effects options. The advantage of this system is that if you have a number of lenses with different filter threads you just need to buy the correct thread adapter for each one and then you can use the system with any of the lenses without having to purchase each filter in each thread size.