There are two major types of photography filters - circular, which screw onto the end of the lens, and square, which are mounted in front of the lens using a special filter mount.

Both types of filters have their virtues, especially if you opt for a filter that's well-made and gives you results that are sound.

Both types of filters also have their advantages and disadvantages.

That means you have a choice to make...

Consult the guide below to determine what type of filter is best for your needs.

Square Filters

As noted earlier, square (or rectangular) filters are most often attached to your lens by using a lens holder, like the one seen above.

These lens mounts can accommodate a variety of sizes of filters and have a host of other hardware that makes the use of square or rectangular filters a breeze. This includes threaded adapter rings and step down rings to accommodate different sizes of lenses.

Square and rectangular filters are made from resin or glass and are offered in a wide range of sizes to accommodate different types of camera systems.

For many photographers, a 100mm filter (like the one shown above) - which is four inches square - is the go-to size. However, you can often find filters that range from 67x85mm to 165x185mm.

Square and rectangular filters can be used for all sorts of purposes as well.

Perhaps most common are neutral density filters that are used to reduce the amount of light entering your lens to achieve longer shutter speeds.

Also popular are graduated neutral density filters, which allow you to darken the sky and lighten the foreground when photographing landscapes for a more even exposure.

Advantages

This type of filter offers photographers plenty of advantages:

• You can use the same filters on many different lenses. With a filter kit like the one shown above, you can adjust the filter holder to meet different lens diameters.
• You can easily stack filters to multiply the power of the filters. For example, you can put a 6-stop and a 3-stop ND together for the equivalent performance of a 9-stop ND.
• Square and rectangular filters often have less vignetting because their surface extends well beyond the edges of the camera's lens.

Disadvantages

Though square and rectangular filters have a lot to offer, there are a couple of things of which to be aware:

• These filters are much larger than their circular counterparts, so care must be taken when using them and transporting them.
• Square and rectangular filters can be very fragile, especially if you opt for a cheap filter instead of one that's constructed well.
• These filters require a bit more setup time as you need to mount them and unmount them when you pack your gear for the next shoot location.

Circular Filters

Unlike square filters, circular filters are made to screw onto the end of a specific sized lens. Naturally, the size of the filter you buy is directly dependent upon the diameter of the lens you use.

However, like square filters, you can get adapters to adjust the size of a circular filter to different sized lenses.

The trick is to buy the filter such that it fits your largest lens, and then use a step adapter to make it fit a smaller one.

For example, if you have a lens with a 67mm thread and another with a 58mm thread, you'd buy the 67mm size and an adapter to accommodate the 58mm thread as well.

Photo filters from outfits like Formatt-Hitech come in a wide range of sizes, from 39mm on the small end to a robust 127mm on the large end.

There is just as much variety in circular filters as there is in square filters as well.

Pick up a circular polarizer, a circular soft-edge graduated ND (as shown above), a circular ND, and even circular UV filters to protect your lens glass.

Advantages

People that purchase a circular filter do so because of the many advantages they provide:

• They're easy to setup. In fact, you can screw the filter onto your lens and simply leave it there for the next time.
• Circular filters are stackable - just screw one filter onto another.
• Circular filters tend to stand up to abuse more so than square or rectangular options.

Disadvantages

When considering a circular filter, bear the following in mind:

• Circular filters aren't a one-size-fits-all solution. If you have multiple lenses of different diameters, you either need to buy filters for each lens or use adapter rings.
• Cheap circular filters can have vignetting, though this isn't a problem with well-constructed circular filters that have a small profile, like the Circular Firecrest ND filter shown above.

Making a Decision

Ultimately, when you buy a filter, so long as it's something that's of a high quality, you can go with a square or a circular filter and get great results.

As noted above, square filters are nice because you can use them with virtually any size of lens.

On the other hand, circular filters are quicker to use because you can simply screw them onto your lens without worrying about using a lens mount.

What it will come down to is what you think fits best with your workflow and the type of lens you feel most comfortable using.