Lens filters can add many enhancing qualities to your photographs. When purchasing a filter, remember that you usually get what you pay for. Hoya and Tiffen are always good filter choices, but are a little pricey. Sometimes, lower quality filters will work fine, but other times, you may have problems such as low performance, low image quality, haze or blur, etc. With a Hoya or Tiffen you are pretty much guaranteed to have no problems. All filters are measured in millimeters, and the size of filter which you need will depend on the thread size of your lens. For example, the kit lens which comes with the Canon Rebel XT is 58mm. You can use larger filters on a smaller lens, or vise versa, with the use of step-up and step-down rings. Below, we will outline the different types of filters, and what they do.
Sky Filters - Reduce blushiness in outdoor shots, especially in shade under a clear sky. Another function of sky filters is that they keep skin tones free of reflections from near objects (such as trees).
Polarizers - Polarizers come in two varieties, Circular Polarizers (CPL) or Linear Polarizers (PL). Generally, linear polarizers are best for manual focus cameras, and circular polarizers are best for autofocus. The reason for this is that with a linear polarizer, many autofocus and metering systems have problems focusing or metering light. When light rays reflect off of a surface, they become polarized. Polarizing filters allow you to basically select which of these light rays you want to allow to pass through. Polarizing filters allow you to remove reflections from any non-metallic surface, such as glass, water, granite countertops, etc. They also increase clarity and vibrance of colors, and drastically improve the appearance of a blue sky. By increasing the contrast between the sky and clouds, and darkening the blue of the sky, they make for some very vivid sky shots.
Differences in sky tones and contrast when using a polarizing filter. Left is without a filter, right is with a polarizer.
Reflection reducing effect that a polarizer has on water. Left side is minimal effect (selected by rotating the polarizer), and the right side is maximum effect.
Neutral Density Filters - Neutral Density (ND) filters are commonly ignored by photographers, but actually have several uses and can help you achieve otherwise unobtainable effects. ND filters work by creating a reduction in light that is neutral amd equal for the sensor area. Some of the uses for ND filters are to decrease depth of field, effectively allowing larger apertures to be used, allowing better seperation of subject and background. They also allow slower shutter speeds (which would normally cause over-exposure) to be used to record movement in subjects such as moving cars, waterfalls, etc. Graduated Neutral Density (GND) filters are neutran density filters which vary the effect with a gradient, which can be helpful when the differences between the highlights and shadows in a scene are too great to be able to properly expose both. ND-2 filters will absorb 1 f-stop of light, ND4 will absorb 2 f-stops, and ND-8 will absorb 3 f-stops.
Comparison showing the effects of both ND4 and ND8 filters on higher exposure and larger aperture.
Star Filters - Star filters, also known as cross screen filters, create a star pattern with lines that radiate from very bright objects, such as lights or reflections of the sun. The number of stars which a filter produces as well as the number of points each star has, varies depending on the filter. Most star filters will be marked as '8 point', '6 point', '4 point', etc. which denotes the number of points each star has.
Comparison between Tiffen star filters.
IR Filters - Infrared filters allow only infrared light to pass through, blocking all visible light.
Intensifying Filters - Filters which intensify one particular color. May be used to make the sky or grass more vibrant, etc.
Diffusion Filters - Diffusion filters give a very 'soft' feel to shots, great for portrait work, in which they are very good at hiding blemishes and uneven surfaces.
Duto Filters - Duto filters work somewhat like diffusion filters, but leave the center of the image very sharp while giving the edges a soft feel. Great for portrait work and professional photography.
Portrait Filters - Portrait filters reduce yellows and oranges but enhance pinks, making skin tones more vivid and clear.
Fluorescent Filters - Fluorescent (FL) filters correct the greenish-yellow tone that fluorescent lighting gives off.
How to Choose a Lens