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Thread: Please explain the purpose of the AA filter

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    Senior Member doug's Avatar
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    Please explain the purpose of the AA filter

    What's the point of an AA filter (on the a7II) if I get this?

    Doug Herr http://www.wildlightphoto.com
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    Re: Please explain the purpose of the AA filter

    Thanks Doug, I think you need more pixels, seriously.
    With best regards, K-H.

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    Senior Member ErikKaffehr's Avatar
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    Re: Please explain the purpose of the AA filter

    Hi Doug,

    It is a combo of sharp lens, exact focus, large pixels and a weak OLP filter. The OLP filter is intended to lower contrast (MTF) at the extintion limit. It is a compromise. Sharper lenses need stronger filters.

    The OLP filter used to be a four way beam splitter using dual birefringent layers with a depolariser between. On recent models Sony only uses one layer.

    My A7rII shows colour aliasing at medium apertures with sharp lenses, so I guess you need to go smaller pixels to avoid aliasing entirely. Or stop down so diffraction kills it.

    Best regards
    Erik


    Quote Originally Posted by doug View Post
    What's the point of an AA filter (on the a7II) if I get this?
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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: Please explain the purpose of the AA filter

    The thing to realize is that the AA filter (or more resolution) help with reducing the chances and severity of moire but ultimately with any bayer array based sensor there's always the chance of both normal interference pattern moire and also the moire caused by the demosaicing from the sensor. I've had both before (bayer pattern moire is much worse btw - think geometric patterns) and ultimately we're just in the business of pushing the effects off to the more and more extreme situations.

    Btw, the C1 Pro moire reduction tool works well but ultimately will soften the moire portion of the image. Selective edits and masking are your friend.
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    Senior Member ErikKaffehr's Avatar
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    Re: Please explain the purpose of the AA filter

    Hi,

    Well, it is a compromise. Really it is not just moiré but also about other aliasing artefacts. The problem is really undersampling, we have more information than the sensor can resolve, to that comes that colour information is even more undersampled.

    The solution is to have a sensor that outresolves all lenses (high MTF near zero at Nyquist), but that may be not realistic for a while:

    • It doesn't play well with pixel peeping, will look awful at actual pixels.
    • Very large files would results
    • Negative effects on DR and risk for cross-talk between sensels


    But, it is really the way to go.

    Best regards
    Erik



    Quote Originally Posted by GrahamWelland View Post
    The thing to realize is that the AA filter (or more resolution) help with reducing the chances and severity of moire but ultimately with any bayer array based sensor there's always the chance of both normal interference pattern moire and also the moire caused by the demosaicing from the sensor. I've had both before (bayer pattern moire is much worse btw - think geometric patterns) and ultimately we're just in the business of pushing the effects off to the more and more extreme situations.

    Btw, the C1 Pro moire reduction tool works well but ultimately will soften the moire portion of the image. Selective edits and masking are your friend.

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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by doug View Post
    What's the point of an AA filter (on the a7II) if I get this?

    Sony try to minimize these in many ways.

    NEX-5 had an AA filter stack. The shutter was secured by 3 screws. But the shot gun shutter still had an impact on sharpness.

    Nex-5N did not have a AA filter stack, the shutter was screwed in by a single solitary screw. (There was No room for the top 2 screws and the slots were left vacant). This is to offset the newly introduced EFCS that minimized the vibrations. The NEX-6 had EFCS and 3 screws. It also had an AA stack (like the NEX-7). All these were engineered with a plastic mount to add a little play so that a lens is not secured too well. These continued on with the A7/7R.

    All the loud noises demanding "better" everything led to a metal mount, EFCS, SSS (that increases the thickness of the body, so something jas to be trimmed down to make it compact) and thinner filters with less epoxy.

    AFAIK, this is the first demonstration of moire (I saw an example from the A7RII and Otus) with the A7II.

    The next iterations will take care of them if there is enough demand for it.

    To mitigate this issue at the moment:
    1. Turn the SSS off.
    2. Turn the EFCS off.
    3. Use a lens that is not APO and wetzlar.

    If I think of more, I will add them later.

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    Senior Member doug's Avatar
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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by Vivek View Post
    3. Use a lens that is not APO and wetzlar.
    It's Solms I ought to use the Canon 500L instead.

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    Senior Member ErikKaffehr's Avatar
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    Re: Please explain the purpose of the AA filter

    Hi,

    The A7rII is prone to moiré. Actually, even the kit 28-70/3.5-5.6 lens is good enough to produce moiré. It is not that bad as I expected, tough. A lot better than my Hasselblad V-series/P45+ combo. Just to say, I discovered moiré on a few of my first dozens of shots. On the other hand I have not seen it on any of a lot of carefully executed shots. It is very subject dependent.

    The presence of moiré indicates that the lens outperforms the pixel size. It is as simple as that. The amount of moiré that Doug's lens produces indicates that it is very sharp and that the sharpness is native and not a result of excessive sharpening. I might start saving for one of those lenses…

    I don't think sensor size is a problem, the optical package is probably equivalent to about 2 mm on all Sony cameras. Replacing two costly components with a piece of optical glass and getting applause from pixel peepers is incentive enough to leave OLP filtering out.

    Best regards
    Erik

    Quote Originally Posted by Vivek View Post
    Sony try to minimize these in many ways.

    NEX-5 had an AA filter stack. The shutter was secured by 3 screws. But the shot gun shutter still had an impact on sharpness.

    Nex-5N did not have a AA filter stack, the shutter was screwed in by a single solitary screw. (There was No room for the top 2 screws and the slots were left vacant). This is to offset the newly introduced EFCS that minimized the vibrations. The NEX-6 had EFCS and 3 screws. It also had an AA stack (like the NEX-7). All these were engineered with a plastic mount to add a little play so that a lens is not secured too well. These continued on with the A7/7R.

    All the loud noises demanding "better" everything led to a metal mount, EFCS, SSS (that increases the thickness of the body, so something jas to be trimmed down to make it compact) and thinner filters with less epoxy.

    AFAIK, this is the first demonstration of moire (I saw an example from the A7RII and Otus) with the A7II.

    The next iterations will take care of them if there is enough demand for it.

    To mitigate this issue at the moment:
    1. Turn the SSS off.
    2. Turn the EFCS off.
    3. Use a lens that is not APO and wetzlar.

    If I think of more, I will add them later.

  9. #9
    Senior Member ErikKaffehr's Avatar
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    Re: Please explain the purpose of the AA filter

    Hi Doug,

    Which lens did you use? I may start saving up for it! Just to say, it is not just about the lens, the man behind the camera matters a lot.

    Best regards
    Erik

    Quote Originally Posted by doug View Post
    What's the point of an AA filter (on the a7II) if I get this?


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    Re: Please explain the purpose of the AA filter

    Using an A7rII rather than an A7II might help somewhat when using an APO-R 280/4.
    With best regards, K-H.
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    Re: Please explain the purpose of the AA filter

    My little trick when I see it in the Evf and I can spot it is to just back focus off ever so slightly. I even got it once with my Batis 85 wide open handheld .one issue is this rII is deadly accurate at AF.
    Photography is all about experimentation and without it you will never learn art.

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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by ErikKaffehr View Post
    Hi,

    The A7rII is prone to moiré. Actually, even the kit 28-70/3.5-5.6 lens is good enough to produce moiré. It is not that bad as I expected, tough. A lot better than my Hasselblad V-series/P45+ combo. Just to say, I discovered moiré on a few of my first dozens of shots. On the other hand I have not seen it on any of a lot of carefully executed shots. It is very subject dependent.

    The presence of moiré indicates that the lens outperforms the pixel size. It is as simple as that. The amount of moiré that Doug's lens produces indicates that it is very sharp and that the sharpness is native and not a result of excessive sharpening. I might start saving for one of those lenses…

    I don't think sensor size is a problem, the optical package is probably equivalent to about 2 mm on all Sony cameras. Replacing two costly components with a piece of optical glass and getting applause from pixel peepers is incentive enough to leave OLP filtering out.

    Best regards
    Erik
    Hi,

    It is NOT 2mm (the sensor UV/IR/AA) stack in the E mount cams. If in doubt measure it yourself as I have. It is all over the place. The A7/A7r have a total of 2.5mm thick glass as in NEX-5. It is likely less in the A7II and the A7rII (they got rid of the dust shaker glass because of the SSS).

    I never said that the sensor size had anything to do with the moire.

    The lens that Doug used is a Leica APO 280/4. The big positive there is that it obviates sharpening and hence no "orange peel".

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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by k-hawinkler View Post
    Using an A7rII rather than an A7II might help somewhat when using an APO-R 280/4.
    The A7R probably is better.

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    Re: Please explain the purpose of the AA filter

    i thought moire was caused by a harmonic between a texture pattern in the image and the pixel pitch and could be improved upon with smaller pixel spacing for example
    aliasing on the other hand , was the appearance of the step pattern in linear edges not parallel to the grid, caused by the digital, not continuous, array, and could also be improved with smaller pixel spacing

    bayer pattern is not so much the problem, implying the bayer-less monochrome could also show moire, but in grey tones?

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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by Vivek View Post
    The A7R probably is better.
    Thanks Vivek? Why?
    With best regards, K-H.

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    Senior Member doug's Avatar
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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by ErikKaffehr View Post
    Which lens did you use? I may start saving up for it!
    You might have to save for a while. As others have noted I used the Leica 280mm f/4 APO-Telyt-R.
    Doug Herr http://www.wildlightphoto.com
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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by k-hawinkler View Post
    Thanks Vivek? Why?
    Shake = defocus, the trick that Guy posted about but in different directions.

    (What I referred to in my earlier post about NEX and the shot gun shutter)

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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by Vivek View Post
    Shake = defocus, the trick that Guy posted about but in different directions.

    (What I referred to in my earlier post about NEX and the shot gun shutter)
    Thanks Vivek.

    On the other hand one could use an A7r2 with IBIS OFF and smaller pixels, no?
    With best regards, K-H.

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    Re: Please explain the purpose of the AA filter

    Doug, Given your excellent techniques honed over the years plus the gear under discussion, the moire isn't going away.

    One possibility that you could try to minimize moire is to make use of the SSS (aka "IBIS") in the camera. Instead setting the focal length to 280 (or 300), you could experiment with a lower focal length thus tricking the camera compensation to be less efficient.
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    Senior Member ErikKaffehr's Avatar
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    Re: Please explain the purpose of the AA filter

    Hi,

    I would say that used APO-Telyts are in a reasonable price span on EBay, but it is still an significant expenditure. Having some good information can be helpful in making the right choice.

    That shot you showed was an interesting input…

    Just to mention, I can buy a Sigma 500/4.5 at half the price or a Sony Alpha 600/4 G APO at twice the price, or I can buy an old Canon or Minolta lens at rock bottom price…

    But, seeing real worlds samples makes you interested!

    Best regards
    Erik

    Quote Originally Posted by doug View Post
    You might have to save for a while. As others have noted I used the Leica 280mm f/4 APO-Telyt-R.

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    Re: Please explain the purpose of the AA filter

    On the A7r2 one can select ..., 180, 200, 210, 250, 300, 350, ... but not 280.
    Which one would be better? I have been using 300 for my 280/4.
    With best regards, K-H.

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    Senior Member doug's Avatar
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    Re: Please explain the purpose of the AA filter

    Quote Originally Posted by k-hawinkler View Post
    On the A7r2 one can select ..., 180, 200, 210, 250, 300, 350, ... but not 280.
    Which one would be better? I have been using 300 for my 280/4.
    I've been using 300 as well with the a7II. Time for experiments!
    Doug Herr http://www.wildlightphoto.com
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