For most photographers, their first experience with a filter is when it is suggested they purchase a UV or Skylight filter to protect their lens. It’s usually much later that beginning photographers find out about the other filters available to them, and what they can be used for.
Once you’ve decided to add a filter or filters to your camera bag, however, you’ll be faced with a myriad of choices regarding the various brands, materials, and types of filters that are available to you. Many times, the gut instinct is to purchase the cheapest filter that will do the job. The reality is, however, that there are many factors to consider when purchasing a filter, and buying the cheapest one on the rack that does what you want, it to is not usually a good idea. There is often a difference in the quality of the materials used, even when both filters appear to be made of the same things.
In An Introduction to Filters for DSLRs, you’ll find a breakdown of the different kinds of filters, and their uses. Here, I’d like to try and demystify the differences between filters, and why similar looking filters might have drastically different price points.
Screw-in versus drop-in filters
First of all, there are two basic types of filters: screw-in and drop-in. The former mount directly onto the lens via the threads on the front, whereas the latter drop-in type are square or rectangular in shape, and require a filter holder and mounting ring that attaches to the front of the lens. Certain types of filters are available as both a screw-in and drop-in filter.
Screw-in filters are constructed of glass with a metal ring. The quality of the glass can vary, even within the same brand, depending on whether you’re going with a high end filter or a value priced one. The metal of the ring can vary as well, as they can be made of brass or aluminum. Cheaper filters usually have an aluminum ring. It’s a soft metal that is more easily dented if dropped, or bent if put under pressure. This could cause the filter to jam when mounting it to your lens. The most popular screw-in filters tend to be polarizers, UV, and neutral density filters.
The other type is what’s known as a drop-in filter. These are square or rectangular pieces of glass that are typically inserted in a holder that is mounted onto the lens. Often, the holder, or mounting ring, can also accommodate a screw-in polarizing filter, as well as two or three drop-in filters in front of that, allowing you to combine the effects of a polarizer, a neutral density filter, and/or a graduated neutral density filter.
While graduated neutral density filters are available as both a screw-in or a drop-in, the drop-in style allows for more precise placement of the gradation, and thus allows for more creativity. Drop-in filters are generally part of system, or have compatibility with one. Some examples include: the Lee filter system, Vü Sion Q system, Formatt-HItech, and Cokin P and Cokin Z filter systems. You’ll want to ensure that the system you invest in has the filters you need available, and that it’s compatible with your size camera.