Camera lens filters used to be incredibly important before digital photography. Nowadays, this isn’t the case. Software filters and post-processing can often substitute for lens filters and they are much more precise. However, even in the land of digital photography, some lens filters cannot be duplicated in post-processing.
The most important lens filter you can buy is a known as a Circular Polarizer. A circular polarizer will make skies deep blue, clouds pop out, eliminate unwanted reflections, and enhance colors. The filter is adjustable so that you can twist it and dial in the exact effect you want.
A polarizer is most useful when the sun is very strong. If it’s a day for wearing sunglasses or sunscreen, it’s probably a day to use a polarizer. Rainbows can also be enhanced by shooting them with a polarizer.
If you have lenses that use different filter sizes, one way to save money is to buy one circular polarizer made for the largest filter size lens you own. For example, if you have two lenses, one that takes 77mm filters and one that takes 58mm filters, you would buy one polarizer that is 77mm. Then you can use an inexpensive adapter known as a “step up ring” to fit the larger filter onto the smaller lens.