If you are up to date with the photographing world, the release of the several high end cameras that lack the AA filter or Optical lower pass filter might have caught your eye. I am taking about cameras such as the Nikon D800E or the Pentax K-5 IIs, which are special versions of the D800 and the K-5 II respectively, but also cameras like the Nikon D7100, and the lastest Nikon D5500, which were released without the filter.
You are probably wondering why these camera versions are more expensive even though they lack of something the normal version cameras have. In this post I will try to explain what this filter consists of, what is it that it normally does and what are its advantages and disadvantages of not having it in our cameras.
Let’s start from the beginning: What is an Optical Low Pass Filter (AA filters)? AA is the acronym for “anti-aliasing”. When the images are processed in a certain way, they can produce unwanted effects such as the moiré patterns. Moiré is an effect that occurs mainly when shooting elements with line patterns or lines too close together. These lines interfere with the sensors pixel grid, thus creating an unpleasant effect to sight. The AA filter that comes with the camera sensor makes sure that this doesn’t happen.
What this AA filters do is to lightly scatter the light that reaches the sensor. Attenuate the higher frequencies and at the same time, let the lower ones through. This rids from the moiré effect, but its drawback is that this affects negatively the general sharpness of the photographs making it lose detail. We could say that this filters are a lesser evil. In summary, we give up some sharpness in exchange of avoiding the moiré effect.
Cameras such as the D800E or the D7100, which lack the AA filter or lower pass filter, promise to deliver that extra sharpness and, in theory, include some other measures to prevent from the occurrence of the feared moiré effect. In the Pentax official website you’ll see pictures taken with both K-5 II versions, so that you can compare the results with and without the filter.
Of course it is possible to disable the AA filter on a camera that has it. There are companies that offer that precisely. But of course, this depends on the type of photographs we want. If the moiré is not going to be an issue for us, we could renounce to the filter and have the extra sharpness. If not, it’s preferable use the filter and gain some sharpness while processing.