Lens filters, which thread on to the end of a DSLR lens, used to be critical to photography. Now that many of the functions lens filters perform happen automatically within a camera’s imaging systems, photographers may question the need for filters. Advanced technology has made some lens filters obsolete, but filters are still useful for some types of photography. Before purchasing a filter, be aware that filters come in different sizes to fit different camera lenses, so a filter for your standard lens might not fit all other lenses you have. Michigan Technical University has a great guide for understanding lens-to-filter fit. There are hundreds of different types of filters, but most fall into five major categories.
Clear and UV Filters
Clear filters are clear glass meant to protect camera lenses, and high quality clear filters have no effect on images taken with a DSLR camera. Lower quality clear filters that are too thick or have imperfections in the glass may cause aberrations or defects in images, but this is true of any low quality lens filter used in photography (for more on the effects of low quality filters with picture explanations, visit Birchtree Photography).
UV filters are also a type of clear glass filter, but the glass will block most UV, or ultraviolet, light from reaching the image sensor. Since most modern DSLRs do not pick up UV light the way film once did, UV filters are not usually required for digital photography except at high elevations. However, many digital photographers use UV filters to protect the camera lens from dust and scratches since it does not affect image quality, and even a high quality UV filter is less expensive than a lens replacement.
Once the most common lens filters, polarizing filters are now nearly obsolete for all but professional photographers. Polarizing filters reduce the amount of reflected light from objects such as water while having the least effect possible on ambient light when proper exposure is used. Since polarizing filters block one or more stops of light, this means that exposure time must be lengthened and necessitates a tripod. The situation where polarizing filters are most useful is in professional landscape photography, especially since autofocus cannot be used with most polarizing filters. Quality polarizing filters are also expensive. The good news is, for most DSLR users, a polarizing filter isn’t necessary.
Before digital color and white balancing, color lens filters were important to ensure accurate color recording, especially in monochrome photography. Now many functions of basic color filters have been replaced by on-board DSLR adjustments. The effects of a few types of color filters can’t be replaced, particularly those filters with the deepest color saturation saturating too deeply with DSLR settings leads to over-exaggerated results. Color-blocking filters can’t be replaced by DSLRs, either, but these effects are usually only used in professional digital photography. As with polarizing filters, for most photography color filters aren’t necessary.
Cross screens are filters of clear glass embedded with ultra-fine cross hatched grating, like a window screen. The cross hatches do not appear in the image, but they cause light points to diffract and appear as "star bursts". The more cross hatches there are the more points to each "star burst". Star-Four, Star-Six, and Star-Eight are the most common. Some DSLR cameras have special effects to replicate this, and it can also be done in photography editing programs, but in this case technology hasn’t caught up to the original. Photographers who want a good star burst effect in their digital photography should invest in a cross screen filter.
Macro lens filters act like a magnifying glass, bringing a macro lens effect to standard camera lenses. Macro lens filters are much less expensive than macro camera lenses, especially for those who are unsure if they want to do macro photography or do not do it frequently. When using a macro filter, a DSLR must be focused manually and focus range is severely limited while a macro filter is in place. However, once photographers learn how to work with a macro filter it can be a worthwhile investment.
Despite calls for the demise of lens filters, certain groups of lens filters still have a place in digital photography. If for no other reason than to protect the expensive optics of a DSLR lens, photographers should use at least a clear glass filter in most situations. Other types of lens filters are essential for creative photography since they have not yet been replaced by technology. For more information on choosing and sizing a filter for your DSLR, d-store has an excellent FAQ page.