cboysen Loc: Homewood, IL

What is the meaning of the above? Is it something positive? I read that it's done to the Nikon D7100, true? Why is it done? Thanks.

houdel Loc: Chase, Michigan USA

The Anti Aliasing filter filter desharpens images slightly to reduce or eliminate Moire pattern in the captured. A Moire pattern shows up when photographing items with a close weave, such as certain fabrics or window screens. Light reflecting from the individual strands in the material interact and insert a secondary pattern in the image. Sorry I don't have a sample photo, but if you imagine a window screen with the same regular pattern imposed on top of the screen but at an angle that is what a Moire pattern would be.

Many modern cameras have the AA filter. The Nikon D800 was made with the AA filter, it was eliminated in the D800E and D810. In lower resolution cameras the amount of desharpening by the AA filter was not significant but as resolution climbed the desharpening became more significant. The current trend seems to be phasing out AA filters in many newer cameras.

KennyMac Loc: Lynchburg, VA

cboysen, google "camera anti aliasing filter", for many explanations and companies that will do modifications such as
http://www.lifepixel.com/blog/anti-aliasing-low-pass-filter-removal

Peekayoh Loc: UK

Sorry but you have this wrong, it has nothing to do with light reflecting from individual strands and causing secondary patterns.

Moiré patterns occur when the subject contains repetitive patterns and when the repetitive frequency is smaller than the pixel grid on the sensor. Obviously, if the detail is smaller than a pixel, it cannot be resolved but it can create the artefacts we call Moiré. The thinking behind the AA filter is that if you can't resolve the small detail anyway, you may as well blur it in order not to create the artefacts in the first place. This is all well and good but it does also create blur where we don't want it. Landscape Photographers hate the AA filter because of the blur and because there are very few instances in the natural world where Moiré patterning would be a problem. On the other hand, Wedding Photographers wouldn't want to do away with the AA filter; a lot of their work includes suit cloth which is notorious for Moiré.

The smaller the photosite, the less need there is for an AA filter but that doesn't mean you won't get it whether you like it or not. For instance, Sony left out the AA filter on the A7r (4.9µm grid) but left it in the A77II (3.9 µm grid); clearly Sony figured the A7r was less of a general purpose camera and that it would appeal most to Landscapers and Portrait Togs.

rbfanman

The Low Pass / Anti-Aliasing Filter is used to reduce Moire...a pattern of broken up patches of various colors which can afflict your images. The filter does a pretty good job of that, but also gives the light that creates your images one more thing to pass through on it's way to the sensor...and that causes image loss / blurring, which reduces the detail your image has.

Moire can be combatted these days by better lens coatings, and by higher Megapixel counts. Cameras which have 24+ MP will not suffer so much from Moire, and so do not need a low pass / AA filter, so camera manufacturers are pulling the filters from many cameras. That gives you sharper images from those AA filter-less cameras. My 24.2MP Nikon D3300 has no low pass filter, while several of it's predecessors had one. My images are quite sharp, and I have seen no Moire yet.

JohnSwanda Loc: San Francisco

Since the purpose of the AA filter is to eliminate Moire patterns, I wonder if anyone has had a problem with Moires with cameras without the AA. I am thinking specifically of the Nikon D7100, which I am considering buying. I shoot a lot of portraits, and I have had Moire problems in clothing with other cameras.

rbfanman

I have no experience with the D7100, but imagine that Nikon did plenty of testing in their labs. If they produced the D7100 without an AA filter, it probably handles most tasks without much Moire. However, if Moire is a concern for you, and you do a lot of portrait work, and Moire is more apt to show up in portraits, maybe you should skip the D7100, and buy a more professional model with a higher MP count...such as the D810. More Megapixels seem to be the solution to Moire.

Peekayoh Loc: UK

Bad advice. Because it has a smaller pixel pitch than the D810, the D7100 is less likely to suffer from moiré-induced artifacts.

Macronaut Loc: Redondo Beach,Ca.

I believe you may have this backwards. The 7100 has a higher pixel pitch (higher density of pixels) than the 810.

Peekayoh Loc: UK

Precisely and that makes it less susceptible to moire.

houdel Loc: Chase, Michigan USA

Actually I am not wrong, both answers are correct. Moire is created by an interference pattern as I stated. If you overlay two pieces of screen but at a slight angle and view them in a bright light you can see Moire with a human eye, no digital sensor required. You can also see Moire in a single piece of screen held at the proper angle to a light source.

In a digital sensor the Moire is not caused by the individual strands in the subject material, it is caused by the interference pattern when its frequency approaches the photoreceptor pitch of the sensor. I guess I could have been more precise in my answer but I didn't think I needed to be so technical.

Read the article in KennyMac's response a little more closely, it clearly states "Moire occurs when 2 or more patterns ..... that are close to the same frequency or pitch ..... interfere with one another causing patterns to appear that are not really there". The Moire pattern captured by the digital sensor is merely the visual effect of the sensor's inability to accurately resolve the interference pattern created by the subject material.

Peekayoh Loc: UK

A technical question requires a technical answer and in this case one relevant to the removal of the low pass filter.
Had you said what you are now saying in your last paragraph, I would not have entered the discussion.

Apaflo Loc: Anchorage, Alaska

Only a single pattern in the scene is required to cause a Moire pattern, and the spatial frequency need not be close to the pixel pitch of the sensor. What the sensor cannot resolve is any spatial frequency higher than 1/2 the sensor's pixel frequency (the sampling rate). Half the sampling rate is known as the Nyquist frequency. Instead of reproducing it accurately, higher frequency information is "aliased" to a frequency equally lower than the Nyquist frequency. (What an Anti Alias filter does is prevent the sensor from ever seeing detail that has a frequency higher than the Nyquist frequency. Except they are not perfect, and some of the signal close to the Nyquist frequency is passed. For that reason Moire in cameras with an AA filter is likely to only exist in a narrow band of spatial frequencies near the Nyquist frequency.)

The reason for what is called "color Moire" is that a Bayer Color Filter Array camera has effectively three different sensors. And when high frequency detail is aliased to a lower frequency (from above the Nyquist frequency to below it) there are phase shifts in the signal due to different filters and other causes which result in effectively a very slight frequency shift between otherwise same frequency signals through each different set of colored filters. It's the interference pattern between those signals that causes the Moire we see. The sensor need not resolve an interference pattern because it never actually sees an interference pattern. That comes after the sensor. When the phase shifted signals are converted from analog to digital, the phase shifts are sampled differently and embedded in the digital signal.