Filters are a very popular and useful accessory for your camera. There are many kinds of filters available for every photography need but, generally, filters serve one of four uses: (1) protection, (2) polarizing, (3) color correction, or, (4) special effects. We will discuss each of these four categories in separate articles but, for now, we will concentrate on a general discussion of what to look for in a filter in terms of quality and application.

Filters can be made from a variety of materials such as plastic or gelatin but, most often, they are made of glass. The most common kind of glass filter is known as a “screw-in” filter because the glass is surrounded by a metal ring that screws on to the end of the lens. Nearly every interchangeable SLR lens will accept a screw-in filter. Many point-and-shoot and “prosumer” cameras will accept screw-in filters, too, but most require an adapter.

It is imperative that the filter is the proper size for your lens or adapter. To determine the proper size for your application, you can look on the back of your lens cap, search on the lens itself or look on the adapter. What you are looking for is a number with a “Ø” symbol before it such as Ø58. In this case, this would indicate that your lens or adapter accepts 58mm filters.

The outside circumference of the filter is the same diameter as your lens so, once the filter is installed, you can continue to use the same lens cap. Also, you will notice that the outside of the filter is threaded. It is tempting to want to “stack” filters on top of each other, but it is a practice to be avoided. With each new filter in the stack, less and less light reaches your camera and your image has to be filtered through more pieces of glass.

Not all filters are created equal. When choosing a filter, it is important to consider its quality. Remember, regardless of whether you spent $100 or $1,000 on your lens, the lens is only as good as the filter you put in front of it. In essence, your picture is being filtered through the filter before it gets to your lens or camera.

This, of course, is one of the major reasons why glass is the favored material for filters. But, even within the range of glass filters, there are many differences in quality.

When it comes to quality, the first thing you want to look for is a good grade of glass. If you pick one of the reputable brands, you will be assured of getting glass that is free of any major distortions or defects. Still, there are many grades of glass available from the reputable filter manufacturers ranging from good to the highest optical quality.

Obviously, it is always best to get the highest grade of glass you can afford. However, the better your lens, the more critical this becomes. It doesn't make sense to spend $1,000 on a really sharp lens only to put an average filter in front of it.

Coatings are another major factor when determining the quality of a filter. These days, most lens manufacturers place a coating on the glass to help control reflections and the amount of light that gets through. Likewise, good filters have similar coatings for the same reasons.

Among the filters with coatings, there are single coated filters and multi-coated filters. As the name implies, multi-coated filters have several layers of coatings that reduce the amount of light that is reflected away from the filter. The difference can be significant, too. A filter with no coatings can reflect as much as 10% of the light away while a single coated filter may only reflect 4-5%. The multi-coated filters reduce reflection to as little as 1-2%.

It doesn't sound like much, but it is really easy to see the difference. When examining the quality of the coatings, you can test a filter in two ways.

The first way is to look directly though the filter the way your camera would. If you place a single coated filter and a multi-coated filter side by side directly on a book or newsprint, the difference is instantly noticeable, especially when viewing from an angle. The image is simply more vivid through the multi-coated filter.

The second way of examining the coatings is to compare reflections on the glass between two filters. To do this, place a long, thin object such as a pen at an angle to the filter and observe the resulting reflection on the surface of the glass. The reflection will be substantially less noticeable on the multi-coated filter.

The final consideration for choosing a good filter is determining the material that the ring is made of. Good filters will have a ring made of aluminum or brass. The construction of the ring is important because it will determine the longevity and ease of use of the filter. A material such as plastic will be more prone to breakage and cross-threading. Also, rings made of certain metals or plastics can be very difficult to remove from your lens, especially over time.

We will discuss the various kinds of filters and what they do in future articles but, to sum up our general discussion on construction, it is always wise to choose the best filter you can afford. If you can, opt for a filter with an higher grade of glass and, at least, a single coating. A filter of this quality will generally always have a ring made of aluminum or brass.

If you follow this advice, you will end up with good, sharp photos and you will have a lot of fun being creative with your new filters.