One of the elements of a digital SLR camera that is probably more hated by the photographers is the filter low pass. On the fall all the blame for the lack of clarity of the pictures and some even ask to be removed from the pattern.

However, almost no manufacturer dares to withdraw because that would also entail some disadvantages. Leica currently has only one type of camera without a filter, since Kodak has withdrawn its DCS 14n that had neither.

The mission of the low pass filter, or filter anti-aliasing (AA), is to avoid the appearance of moiré in some photographs in frames leaving a certain size, and the jagged diagonals. Moire is caused by two interference patterns or patterns that overlap. In this case one of the patterns would be the grid of pixels in the sensor, and the other cuaquier repetitive structure (eg a wire cage) that is recorded in the picture with a line spacing similar to that between the pixels.

To avoid introducing an optical element which suppresses the higher frequencies and passes the low (hence the name low-pass), ie, eliminates the finest frame image producing an effect of loss of sharpness in the entire photo . In fact, the result is that transitions between the two tones are not sharp (white to black), but soft (with a weathered gray in between). That is what is known as low acutance and what makes us perceive as less focused photos.

The filter is still used because the low acutance can be rectified by software , while the moiré is not possible, however this requires using a post-processing which apply some kind of mask approach that actually should be called acutance mask.

Some companies offer the service of removing the AA filter on some models of cameras, thus making them more definition models, but always be aware that this may impact on other problems in certain images.

For example, in MaxMax offer this service and several photos of comparing the results with modified and unmodified cameras where you can see clearly the differences to decide what is best for us, if you keep working after the filter and unsharp mask, or not have it.