Drop-in vs screw-in filters
There are two main types of filters available and the option you pick usually depends on your budget. Screw-in filters, as the name suggests, screw on to the front of lenses and are small, lightweight and generally less expensive than the drop-in type. Their disadvantages, however, are that you have to buy them in the right thread size for each of your lenses, so you can end up with two or more of the same filter type.
Drop-in filters drop into a holder that attaches to the front of lenses via an adapter ring, and to use them on different lenses you simply need the appropriate size adapter ring for each lens. The main advantage here is that you only need one set of filters for all lenses, and filters such as ND grads, while available in screw-in versions, are much more effective when they’re the drop-in type.
The most common filter companies include Lee Filters, Cokin, Hoya, NiSi Filters, Formatt- Hitech, Kase Filters, B+W and many more. Drop-in/sheet filters also come in different sizes with 70mm specifically for smaller mirrorless cameras, 100mm for most cameras and lenses, and 150mm filters for use with ultra-wideangle lenses such as the 14-24mm f/2.8 and wideangle tilt-and-shift lenses.
Screw-in filters are small and lightweight