That mysterious AA(anti-aliasing) filter – do you need it?

by planetmitchLeave a Comment

I've known about anti-aliasing filters for a while but I've not taken the time to really dive in and understand exactly what it does… and with the release of the Nikon D800 (pre-order on B&H) and the D800E (pre-order) you start to wonder if do you really need it? In a nutshell, its purpose is to reduce some digital artifacts but it also sacrifices a bit of sharpness.

I've heard of people paying to remove theirs, but isn't something done often and needs to be done by a pro (here's a shop (MaxMax) that seems to have a good rep around the ‘net). And then with the 5D2, we had one manufacturer create another filter to add in front of the AA filter to reduce moire. Maybe that's the wrong solution…

Maybe someone (Canon) should create a DSLR where you can swap it in and out like you can with the ND filters on the Canon EOS C300? After all, there might be times where you need it and times where you want the absolute clarity right?

Anyway, last night we saw a tweet that pointed to this excellent article over on Luminous Landscape “The Naked Sensor” that goes into some great detail about the AA filter you should read!

A snippet to get you interested

A little more than a year ago Michael Reichman, Nick Devlin and I were all sitting down to lunch in a cafeteria at the Jacob Javits Center in New York City. We were there for the annual PDN Photo Plus show and the conversation was largely about which new cameras seemed most interesting to us. "For me", I said, "It's the Fuji X100. Fuji is now trying to out-Leica Leica." And what I meant by that was that Fuji had introduced a competitor to Leica's X1 that not only looked a lot like a Leica M camera – complete with various analog controls – but which also featured a window finder with frame lines. That type of window finder has been integral to the Leica M camera line since it was first introduced and Fuji did a good job of integrating such a finder into the X100 (albeit without a rangefinder). The "M" in "M camera", of course, refers to "messsucher" – the German word for rangefinder.

That lead us to a conversation about whether or not the X100 had an AA (anti-aliasing) filter and, if so, how strong it was. The Leica M8 and M9, of course, have no such filter. As some may know, I've been arguing – over the past few years now – for the advantages of cameras that do not use these filters. In our lunch time brainstorming I suggested that at some point in the not too distant future we were going to be seeing more and more cameras with either very light AA filters or none at all. In my mind, then and now, the AA filter is one of the key elements that "throttles", so to speak, the potential of a digital camera. I noticed this, emphatically, when I was testing a set of Zeiss ZF SLR lenses on both the Nikon D700 and the Canon 1Ds Mk III (the latter via an adapter). Again and again I saw much higher resolution (from the exact same lens) when it was mounted on the 1Ds Mk III. Now, of course, the files from the Canon were dimensionally larger (given its 21 MP sensor as compared to the 12 MP sensor of the Nikon) but what I came to realize was that what I was really seeing were differences between a camera with a stronger AA filter (the Nikon) and one with a weaker AA filter (the Canon). Like many photographers, I'd long known about this difference but that experience sharpened my sense of how important this factor could be.

The purpose of an AA filter, of course, is to slightly blur certain high frequency detail so that it doesn't create artifacts in a camera which uses a Bayer Pattern sensor. The most notable of these artifacts, of course, is moire (a word apparently derived from a French term for a certain kind of textile). And indeed, textiles with certain fine patterns can very often provoke moire in a Bayer-sensor digital camera without an AA filter. I know this first hand, having photographed many weddings with Leica M8 and M9 cameras. Kodak experimented with making small format DSLRs (such as the DCS 14n) without AA filters and Leica obviously decided they wanted to nothing to do with a device that would blur detail in their DMR back (for the R8/R9) or, later, their DRF cameras or, later still, the S2. 

Read more of this excellent article

The story is: The Naked Sensor.

So have you had your's removed?

Sounds like a medical question doesn't it? If you've removed yours, please let me know down in the comments – was it good for you?

I'll tell you there have been times where I've wondered if I should remove mine. [source: tweet from photoxels]

(cover photo credit: snap from the article which has this caption: “Leica M8 File Converted in C1 DSLR Pro (Left version as converted, right version spot corrected for moire.)”)

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