Cameta 101: What Does a Low-Pass Filter Do?

Over the past few years, a number of high-end cameras have been offered by manufacturers with and without a low-pass — or anti-aliasing — filter. Typically, the only differences between each camera model are resolution and price. Examples include the Nikon D800 and higher-priced D800E, or the Canon 5DS and more expensive 5DS R. Recently, however, low-pass filters are being cancelled out or eliminated completely on many advanced cameras. So what is a low-pass filter, what does it do, and what does it mean to you?

What does a low-pass filter do?

A low-pass filter is designed to eliminate the effects of moiré. Moiré is something that shows up in photographs that include repeating lines such as stripes or fences, or very fine patterns, especially in clothing. Usually it results in strange, wavy patterns and color aberrations (see title picture above). A low-pass filter blurs the light that reaches the sensor which helps eliminate moiré and color shifts, although the final image is slightly softened. The Nikon D800 and the Canon EOS 5DS digital SLR cameras — as well as virtually all consumer-level cameras — have a low-pass filter to keep this effect at bay.

Many professionals, however, prefer the increased sharpness and resolution that a camera without a low-pass filter (or one that effectively cancels out the low-pass filter effect) offers, and simply deal with any moiré issues in post-processing. The Nikon D800E and Canon 5DS R are examples of high-end DSLRs that have had their low-pass filters cancelled out.

In terms of sharpness, the difference between cameras with and without low-pass filters is not extreme, but it is noticeable, particularly on object edges. When comparing the pictures below (shot with a Canon 5DS and 5DS R), they look identical until you look up close. The edges of the petals in the photograph taken with the Canon 5DS R are slightly sharper.

Taken with Canon 5DS: Low-pass Filter
Canon 5DS: Close up

What are the benefits of having a camera that cancels out or does not include the low-pass filter?

In short, these cameras produce sharper images and have more information that reaches the sensor. The Nikon D800E and Canon 5DS R digital SLR cameras cancel out the low-pass filter through the use of an additional specialized filter over the image sensor (which contributes to the higher price). The fine details that are important in portraits or macro photos will be nice and sharp.

Low-pass Filter: Blurry
Low-Pass Filter Cancelled: Sharp

Should I buy a camera with or without a low-pass filter?

Cameras that cancel out or don’t include a low-pass filter are especially good for studio and landscape photography. This type of photography requires extreme sharpness and detail, and dealing with moiré is usually not an issue in a controlled studio environment or in nature. In addition, this comes in handy when making large prints so that there is fine detail throughout the entire image.

Photographers who don’t need extreme sharpness and who photograph subjects with repeating lines, street scenes, architecture, or any patterned clothing would be better off with a camera that has a low-pass filter. If your final work is going on the web or you will be making small prints then a low-pass filter camera works well. Also, cameras with low-pass filters are cheaper than cameras that cancel out the low-pass filter.

When making a purchasing decision, keep in mind the type of subjects that you photograph as well as how your final work will be displayed.

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