Downsides to no AA filter

Started Sep 14, 2012 | Discussions thread
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PK24X36NOW Senior Member • Posts: 1,723
Re: Differences in how it is implemented

Petroglyph wrote:

As I understand it, the purpose of the AA filter is to create the "circle of confusion" and either the Nikon or the Pentax solution of removing the AA filter may actually be introducing a little de-focusing of the image which might degrade the image slightly but also might help with aliasing artifacts. Sorry I can't say much about how the Nyquist limit applies because I always understood it more in relation to the sampling theorem of sound digitization and am not sure how to apply it to sampling 2d surfaces. Anyway my point was the first sentence and don't know which solution is better but I'm not happy to hear Pentax put glass in there. It might still turn out Okay we'll see when DXO Mark gets a hold of one.

The purpose of AA filters is to blur frequencies of repetitive fine detail patterns higher than those that the sensor can actually resolve, generally, so that moire (i.e., "false" detail caused by detail too fine to be resolved by the sensor) is avoided. Some cameras have strong AA filters and some weaker, and even with an AA filter, depending on how strong, how much resolution the sensor has, and what fine/repetitive detail is present in the image, etc. you can still get moire occasionally. The AA filter accomplishes this by blurring the image somewhat, which blurring is intended to be reversed by sharpening (of the actual detail resolved) once the "false" detail has been avoided by the blur introduced by the filter.

I doubt there is any meaningful difference in the replacement of the AA filter with optical glass vs. the blur in one plane/cancel filter package that Nikon uses, because the end effect is the same, that is to do away with the AA filter blurring effect, with the related increased chance that you'll see moire in your images.

As for "circles of confusion," those will be present with or without AA filtering.

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