The white balance feature employed by digital cameras negates most color added by external filters attached to your lens. However, there are several types of filters that still work and should be included in your camera bag.
It is true that most lenses have excellent UV coatings so putting a UV filter on your lens is a bit redundant. Yet, these ‘clear’ lenses can still provide protection from things that scratch like, dirt, sea water, branches etc. It is much cheaper to replace a $20 filter than it is to repair or replace the front element of your lens. Some may argue that you shouldn’t put a cheap filter on an expensive lens, but the quality of the filters these days is good, and the protection a filter provides far outweighs any loss of quality.
Circular polarizing filters are designed to cut highlights and specular highlights. They also turn your sky blue and can make white puffy clouds really stand out. By turning the outside of the filter, you can adjust how much polarization you want. To maintain a natural looking image, you should only use the lower (least) half. If you use too much, your the sky will be too blue and the contrast too high, leaving you with a distorted looking image. Play around with the filter to see which setting work best for you. These filters work very well on water as they remove most of the specular highlights and enable you to see into the water instead of just the surface. These filters work best on sunny days and are most effective used at a ninety degree angle to the sun. Regardless of what the salesman in the camera shop says, unless you have reflections, polarizing filters are not effective on cloudy days. Keep in mind, that using a polarizer will reduce the amount of light through your lens by .75 – 2 stops depending on how much you use. In order to avoid any potential metering errors, make sure to get a circular (NOT linear) polarizer for your digital DSLR. You cannot replicate the effects of a circular polarizer in Photoshop. It is possible to simulate some of the effects, but for cutting highlights, use a polarizer. Many pro’s consider this filter to be an essential part of their kit and never leave home without one.
Graduated Neutral Density filters
Graduated neutral density filters are clear on one half and slightly darker on the other. By aligning the darker half with a light sky, you can balance the contrast in an image enabling you to meter more effectively. These are usually rectangular and require a filter holding system that screws onto the front of your lens. These filters come in different densities or ‘stops’ (darkness) and are usually graduated, meaning there is a smooth transition from one end to the other. This ensures the filter is not visible in your shot. These work particularly well for landscape images with a dark foreground and light sky.
Neutral Density filters
These are similar to a graduated filter, but these are consistently dark from one end to the other. They do not add or affect the color, but intentionally darken your image. If you are shooting a river scenic on a bright day, there may be too much light for you to slow down the image enough to blur the water. Using a neutral density filter will darken your image enough for you to use a shutter speed slow enough to blur the rushing water. These filters usually come in 2 or 3 stop varieties.
A few other notes about filters:
1) Most of these filters can be replicated in retouching programs like Photoshop, though the techniques can be advanced and time consuming. For simple warming or cooling filters, simply add a “Photo Filter” layer and choose the color temperature you want. To replicate the graduated neutral density filter you must shoot the image twice. Expose once for the foreground or darker part of the image, and then for the second shot, expose correctly for the light part of the image. Then combine the two images in Photoshop. This works best for still images, since it is very difficult to blend images that do not match up exactly. Keep in mind that extensive adjustments in Photoshop can degrade the quality of your image.
2) When purchasing any round filter for your lenses, the size of the front element should be marked on or near the front of the lens. The size is usually given in mm.
3) The adage “You get what you pay for.” holds true when buying filers. The moderate and more expensive filters will be of much higher quality. When buying filters, look for coated or super-coated filters. For round filters, Tiffin and Hoya make good filters at reasonable prices. B+W and Heliopan are excellent, but a bit more expensive. For square or rectangle filters (NDG or ND Filters) Singh-Ray, Hi-Tech, Lee all make very high quality filters. These filters also require a holder so make sure that the filters you buy fit your holder i.e.. square filter in a holder designed for a rectangle. Conkin makes popular holders.
Though many filters can be replicated in Photoshop, several should still be in your bag. Have them ready, learn to use them and you can bring your images to the next level.