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I have read on some camera reviews that they don't have a low pass filter and therefore they have sharper images.

Since I am a novice, I wonder what is a low pass filter and is it good to have one on a camera?

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A low-pass (or anti-aliasing) filter adds a little bit of blur to the image, which is helpful in avoiding moiré patterns. Moiré patterns are caused when two similar patterns interfere with each other, causing a much more noticeable (and usually unwanted) pattern, like this (image from P. Fraundorf):

moiré

What you have here is two sets of parallel lines that, when placed slightly askew and one atop the other, cause a pattern of dark and light lines. The pixels in a digital camera's image sensor are arranged in a grid, and any sort of closely-spaced vertical or horizontal lines in your image can therefore create a moiré pattern in the final image. The low-pass filter adds a small amount of blur that doesn't significantly change the image overall, but still reduces the moiré effect.

It's true that some cameras come without the low-pass filter. A great example is the Canon 5DS R, which is exactly the same as the 5DS except that it lacks the low-pass filter. And you can see from the product page that Canon warns about moiré with this camera:

The possibility of moiré and color artifacts is greater due to the LPF cancellation function.

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  • \$\begingroup\$ So, is it good to have it on a camera? \$\endgroup\$
    – Omid Kamangar
    Commented Oct 19, 2015 at 16:44
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    \$\begingroup\$ Depends what you want. Basically, there's such a thing as "too sharp" for general photography. I think manufacturers include a low-pass filter on most of their cameras because it yields better images. But as with most things, whether it's "good" or not depends on your needs. If you're a novice looking to get into digital photography, it's probably better to have an antialiasing filter than not to. \$\endgroup\$
    – Caleb
    Commented Oct 19, 2015 at 16:56
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    \$\begingroup\$ @Ako most of the time it makes little difference. To see moiré in your image you need to have very fine detail in your scene, and a very sharp lens with perfect focus and the right F-stop and no motion blur. Certainly you can find examples, but it's rare. The ability to get away without a filter goes up as the sensor resolution goes up. \$\endgroup\$
    – Mark Ransom
    Commented Oct 19, 2015 at 22:22
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    \$\begingroup\$ With the highest resolution sensors, the resolution limits of the lenses themselves begin to function as the AA filter. And many times moire attributed to the sensor is actually caused by scaling errors when the image is resized for viewing. \$\endgroup\$
    – Michael C
    Commented Oct 20, 2015 at 2:35
  • \$\begingroup\$ good explanation. Possibly of note is that some recent camera bodies (I am only aware of the Pentax K3) have no physical filter but are able to simulate one by moving the sensor during the exposure. \$\endgroup\$
    – Joseph Rogers
    Commented Oct 20, 2015 at 13:08

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