Filters have been around for almost as long as cameras. Not only are there many types of filters, there are potentially unfamiliar terms and naming to go with them. Those that are new to filtering may find the options confusing. Hopefully I can help alleviate some of the confusion.
Filter Systems
There are basically two common types of filter systems, each with their own advantages. The round threaded filters, being the most common, come in many sizes so they can easily attach to a lens. Step-up or step-down ring attachments will allow a lens to use a filter of differing sizes. Round threaded filters may turn, but are limited in the adjustments they can make. Additionally these filters typically have front and rear threads to stack filters. When doing so, vignetting (the darkening of the corners in an image) may occur. Modular slot-in filtering systems alleviate the size and vignetting issues. Since slot in filters come in large squares, the filter holder will require an attachment to fit to a lens permitting each filter to potentially be used for every lens in your camera bag. Since the filters are slid into place, setting certain filters in place can move the point of impact on a graduated or split filter. Plus, vignetting ceases to be a concern with these filters since they are larger than the front lens element, even when stacking. There is no reason to avoid either system all together, although the slot-in system tends to be more versatile. One can easily make a case for one or the other, and even a mixture of both.
Are Filters Necessary?
Filters are chosen for how they interact with light, and therefore how they affect the image taken. In some cases, filters are more important when shooting with film than they are when shooting digital. An FL-D filter is used to correct the greenish tint from fluorescent lighting when shooting on film. A simple white balance setting on modern digital cameras makes an FL-D filter as well as warming and cooling filters obsolete. Tinting filters can also be added and adjusted in software like Adobe Photoshop. A single image can be tinted in many ways and with greater control, making the filter potentially less desirable. Additionally adding a filter to the front of a lens will reduce image quality, even though the reduction isn't always noticeable. However there are certain filters that cannot be reproduced in the camera or by using software. Polarizing and neutral density filters cannot be easily reproduced using software if at all. Getting the shot right in the camera can save a lot of time spent in front of a monitor as well. For this reason, filters are still needed. We just don't need as many as we did with film cameras.
Filter Naming
Even though filters are not as important in digital photography, Photoshop uses established filter naming conventions. The filter's name indicates the type of filter it is, as well as indicating strength when options are available. A Skylight 1B filter is stronger/more effective than a Skylight 1A. A 0.6 Neutral Density filter is stronger/more effective than a 0.3 ND filter. A list of filters with their names and purposes can be found at
Filter Manufacturing Terms
Filter manufacturers use some terms like multi-coated that may confuse buyers. Multi-coated indicates the manufacturing process. HMC and MRC are brand specific terms indicating a multi-coated process as well. In theory, more coatings translate into a better more effective filter. The coatings may be for differing purposes too. For example the base coat may achieve the filter's intended purpose, another coat may be added to reduce reflections or ghosting, and a top protective coating may be added for cleaning without damaging the coats underneath. With digital photography, digital multi-coated filters are becoming available. This just means the filter has been coated to work best with a digital camera. This doesn't mean a non-digital multi-coated filter won't be effective on a digital camera though.
