Anti-aliasing blurs the sharply defined lines to smooth things out. the D800E show how the anti-aliasing filter, or optical low-pass filter, works (D800) and how its effect is negated (D800E).ДЄliasing occurs when lines in the photo cross rows or columns of pixels on the sensor. When the D800 and D800E came out, Nikon created quite a stir around the notion of anti-aliasing filters and why they might not be as necessary today. But it also reduces sharpness at the pixel level. This blurs the imageвЂ™s high frequencies (fine detail) at the pixel level, reducing moirГ© and artifacts. (The missing colors are provided to each pixel via interpolation using data from neighboring pixels and complex proprietary algorithms this вЂњdemosaicingвЂќ process also creates color moirГ©.) Since SigmaвЂ™s Foveon sensors do record all three primary colors at every pixel site, theyвЂ™re less susceptible to color moirГ© problems, and thus havenвЂ™t needed AA filters.ДЄ typical AA filter consists of a top layer, which slightly displaces the image horizontally, an infrared filter to eliminate unwanted infrared radiation and a bottom layer that slightly displaces the image vertically.

Conventional Bayer image sensors add color moirГ© to the mix, since each pixel вЂњseesвЂќ only red, green or blue. So the absence of AA filters isnвЂ™t new, but their absence in mainstream DSLRs and mirrorless camera is.ДЄn AA filter, aka OLPF (optical low-pass filter), sits over the image sensor and does away with aliasing-artifacts and moirГ© that occur when you sample the real world with a fine grid of pixels. Medium-format digital cameras-whose users buy those big, expensive beasts because they value image quality, above all-donвЂ™t have AA filters because those users would rather deal with aliasing and moirГ© in postprocessing, when necessary, in return for those resolution benefits. SigmaвЂ™s DSLRs and fixed-lens DP Merrill and dp Quattro models use the unique Foveon X3 sensor that inherently minimizes color moirГ© and aliasing, and thus have never had AA filters. So whatвЂ™s the big deal? What does the AA filter do? Why is it in the camera in the first place, and why should landscape photographers, in particular, be paying attention?ДЇirst, there have been cameras without AA filters for a long time. There are also fixed-lens cameras with no AA filter from Fujifilm, Sigma and Sony. As of this writing, Canon, Nikon, Pentax and Sigma make DSLRs and Fujifilm and Sony offer mirrorless interchangeable-lens cameras with no AA filter. Shortly thereafter, other DSLRs and mirrorless models began to appear with AA filters either negated or removed. Since an AA filter slightly blurs the image at the pixel level, its absence (or negation) means potentially sharper images, albeit with a greater possibility of aliasing and moirГ©. In 2012, Nikon introduced the D800 and the D800E, which were identical, but the D800E had the effects of its anti-aliasing (AA) filter removed.

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