"Shimmering" manual focus

Discussion in 'This or That? (MFT only)' started by DJB, Jun 10, 2012.

  1. DJB

    DJB New to Mu-43

    2
    Jun 5, 2012
    Hi, I'm trying to get into digital photography after shooting nothing but film up until last year, and I'm interested in finding a way to use my Voightlaender and Russian M-mount lenses on a digital camera. While the consensus seems to be focus peaking (as on the NEX) is the best way to focus manual focus lenses, I'd think all the added lines would get in the way of composition, and the micro-4/3 is a more mature system, particularly when it comes to wide-angles.

    Lately, I've been reading about the shimmering technique where apparently when the lens is focused correctly, those areas in critical focus seem to shimmer. Overwhelmingly, people seem to do this using the VF-2 viewfinder. I was wondering if anyone had any experience focussing this way with other viewfinders, if it is easier or harder on these viewfinders, and what to look for in a camera or viewfinder that makes focusing this way straightforward.

    Thanks for any advice on this or other tips on using this focusing technique.
     
  2. RevBob

    RevBob Super Moderator

    Jun 4, 2011
    NorthWestern PA
    Bob
    I've never really seen the "shimmering" (though I have read about it on this forum) but I do know that legacy lenses are very easy to focus on :43: cameras. I have several different Olympus cameras and several legacy lenses - I love using them. :smile:
     
  3. Lawrence A.

    Lawrence A. Mu-43 All-Pro

    Mar 14, 2012
    New Mexico
    Larry
    I've been using manual focus lenses all my life, and I don't know what "shimmering" is. Focus on a specular highlight and you'll know when it's sharp. On the m4/3 cameras enlarging the viewfinder image makes things very easy.

    I don't know. I never liked split screen focusing aids, and always switched them out on my OM 1 35mm cameras to put in a grid screen with no aid. I found focusing easier when just -- well -- focusing. Human eyes are pretty good at it.
     
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  4. penfan2010

    penfan2010 Mu-43 All-Pro

    Nov 12, 2010
    NJ, USA
    DJB - I read about this effect a year or so ago, and when I finally got my VF-2, I did notice the shimmer effect on the part of the image that was in focus when using my legacy Zuiko and Leica MF lenses. The effect tends to be more obvious when the subject you are shooting has good contrast and lighting. It's not as obvious as the film 35mm split screen or the ground glass collar surrounding it, but it helps. The only other EVFs I've used, albeit briefly, were on the Panny G1 and G2. The EVF image was not as good as the Olympus VF-2, and I do not recall seeing the same "shimmer", though that does not mean it doesn't manifest itself on those EVFs. Hope this helps.
     
  5. lenshoarder

    lenshoarder Mu-43 All-Pro

    Nov 7, 2010
    I'm familiar with the shimmering. You don't need to use a EVF to see it. It shows up on the LCD. It does kind of work like peaking on a NEX, but is not as realiable in terms of when it happens. It happens in very high contrast areas. It works best with very thin lines. It looks more like old school interlace flickering than anything else. I can make it happen at will with my ISO chart. Maybe I'll take a video of it happening tomorrow and post it.
     
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  6. rpress

    rpress Mu-43 Regular

    76
    Jun 11, 2010
    "Shimmering" is caused by aliasing. This means that the lens resolution is higher than the anti-aliasing filter on the sensor. When aliasing occurs, it's not really a good thing as it can show up in the final image.

    I don't really notice it on my G3, but I've heard the Olympus cameras have weaker anti-aliasing filters, and therefore are more likely to have the shimmering.
     
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  7. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    In this case, aliasing means that the resolution is higher than the display device, which is not the sensor, but the LCD or the EVF. As a result, real aliasing (the kind that is visible in the actual image) is much rarer.

    DH
     
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  8. rpress

    rpress Mu-43 Regular

    76
    Jun 11, 2010
    I would expect that the LCDs would use bicubic interpolation, and therefore anti-aliasing, but maybe this is not the case on all cameras. It would be easy enough to see if the saved image has aliasing when the LCD shows this "shimmering."

    If it is the case of only the display aliasing, then "shimmering" will not be a good indication of correct focus, it will only show you have exceeded the display resolution and not the sensor resolution.

    I've seen your photo posted here that show substantial aliasing on Olympus bodies, so I wouldn't call that rare.
    https://www.mu-43.com/f74/moire-lightroom-24318/
     
  9. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    No, it's fairly good (obviously viewing at 100% mag is better, but it's a start). You're not going to get shimmer unless there's a good amount of fine detail, and if the focus is off by much, there'll be no detail to speak of.

    Aliasing in images with lots of straight (or nearly straight) lines isn't uncommon. But you can get the VF shimmer on virtually any image with proper focus and any sort of detail. Nature photos for example rarely show much aliasing, yet I can easily get the 'shimmer' when I'm near the proper focus.

    DH
     
  10. rpress

    rpress Mu-43 Regular

    76
    Jun 11, 2010
    In practical terms, it might not matter much, but do you see my technical point? The screen resolution is a lot less than the sensor resolution, especially using the EVF. If the screen is aliasing this doesn't guarantee the maximum sensor resolution. If the sensor is aliasing, this does mean you are at maximum sensor resolution.

    Just because you can see the aliasing with straight lines, doesn't mean it isn't there in other photos; it just doesn't look bad. The shimmering effect is really a combination of aliasing and movement (while framing the shot) and this aliasing might not look bad in the saved image.
     
  11. DJB

    DJB New to Mu-43

    2
    Jun 5, 2012
    Thanks for all the great responses. With any new technique, I have a lot of questions; I'd rather not make an incorrect choice on my first mirrorless purchase.

    Reading through the excellent comments on this thread, I have two questions: first, is "Moire in Darkroom" showing plain semi-static moire due to weak anti-aliasing on a patterned object, or was the shimmer captured right at the moment of critical focus? (Or am I making a false distinction?) It would seem odd if people are using this shimmering for critical focus if one actually loses sharpness (as seen in the photos) if one captures in the middle of the shimmer, yet one couldn't see the shimmer in the capture if only the screen were getting aliasing from the sensor.

    Second, wouldn't this be a huge effect with live view on a medium format back given it has lots of resolution with no anti-aliasing filter?
     
  12. rpress

    rpress Mu-43 Regular

    76
    Jun 11, 2010
    It's not the point of critical focus, it's really the X/Y movement of the image on the sensor. In the case of aliasing on "straight" lines, X/Y movement will just move the funny colors around but they will still be there.

    A higher resolution sensor is better. This could mean that you have more sensor resolution than optical resolution, depending on the lens. And this is what you want. Aliasing occurs when your sensor has less resolution than the optics. An anti-aliasing filter basically "forces" the optics to have lower resolution than the sensor.


    This is how I see the shimmer effect occuring:

    1) The optical resolution (lens) is higher than the sensor resolution.
    2) This allows aliasing to occur - basically this means that high frequency information (most notably vertical/horizontal lines, but can be anything really) will not be digitized correctly.
    3) Instead of having equal intensity on the Bayer filter of the sensor, the high frequency information only illuminates one/some of the color filters over the imaging sensor.
    4) This produces funny colors at these high frequency areas.
    5) If the camera is moved just slightly relative to the scene, the high frequency information will move from one color to another.
    6) This effect looks like "shimmering."

    Technically aliasing does not lose sharpness, but what it does is create false information that was never there. Unfortunately, once the image is captured it's "impossible" to know what is fake and what is real. However in the real world it's not very common to have funny colors next to straight lines so I guess something could be done in post to correct for this problem.
     
  13. chicks

    chicks Mu-43 Top Veteran

    876
    Feb 1, 2012
    The Big Valley, CA
    Huh. That's kinda cool. Was taking some pictures of my vintage gear, and noticed some shimmering along the line just between the shiny metal faceplate and the dark brown bezel. I was at at angle to the face, and noticed that the shimmering moved along the line as I changed the focus. Set it at the middle, and the shot was perfectly focused right at that point! No MF assist required.
     
  14. albert_ang

    albert_ang Mu-43 Regular

    26
    Jun 5, 2012
    Melbourne, Australia
    I'm still confused, what's is a "shimmering"? Can someone show me the photo of your lcd when that happens? Is it a phenomena only occurs in the old lenses or to VF2 only? I'm not aware it happens when I'm manual focusing using the current m43 lenses.