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E-M5 backfocusing during C-AF+TR

Discussion in 'Olympus Cameras' started by Stubb, Sep 4, 2012.

  1. Stubb

    Stubb Mu-43 Regular

    Apr 23, 2012
    Atlanta, GA
    I've followed the advice in this post but am getting numerous backfocused images during C-AF+TR operation with my E-M5. This is all with subjects coming toward me (roller derby, parades). I have the camera set in single-shot mode and am taking three or four images. There's typically one that's good enough with the others being backfocused by 1–10 meters. This is with the Olympus 45 f/1.8 or 14–140. Anyone else run into this problem or have advice?

    S-AF on the camera has been boringly accurate, even in bad light. The AF areas do cover too much of the subject IMHO, and I find that the camera tends to focus on the back part of the highlighted region. But that's not a big deal.

  2. b_rubenstein

    b_rubenstein Mu-43 All-Pro

    Mar 20, 2012
    Melbourne, FL
    Backfocusing is a form of defective AF operation when a camera focuses behind a stationary subject.

    You're just getting out of focus pictures. If the camera is set to Sequential H, whatever focus is used for the first frame is used for all the following until you lift your finger. Try using Sequential L, or just stick with AF-S. To get what you want in focus, zoom in. (see pg45 of manual).
  3. Stubb

    Stubb Mu-43 Regular

    Apr 23, 2012
    Atlanta, GA
    Perhaps backfocus isn't the best term, but I'm getting out-of-focus pictures in C-AF+TR mode where the plane of sharp focus is behind the subject. In the 100+ pictures I've gotten like this, there hasn't been a one where the camera missed to the front. I don't have sequential shooting enabled at all.

    I haven't tried using the variable-sized AF block in C-AF or C-AF+TR mode. That's a good suggestion. Spending more time with plain C-AF might be a good idea as well.

  4. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    It sounds like a case not of the camera focusing in the wrong place, but of the camera focusing at a time prior to the exposure. That would account for all of the errors being focus behind the subject (focused where the subject was in the past) rather than focused in front (focused where the subject will be in the future).
  5. The problem is that the camera is measuring the focus point based on where the subject was rather than where it predicts they are going to be. If the subjects were heading away from you you would likely have the opposite problem of them being behind the focal plane. The only focus mode that I really use and trust is S-AF using the smaller focus box.

    Since you're not using the sequential shutter it is probably best to use S-AF anyway. S-AF tries to acquire focus the instant before shutter release, whereas C-AF is constantly re-adjusting and the AF timing probably isn't matching up with the shutter release.
  6. Stubb

    Stubb Mu-43 Regular

    Apr 23, 2012
    Atlanta, GA
    Thanks for the suggestions. These give me some things to try my next time out.

  7. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    If the focus area is too large it will focus from the furthest point first (I think, so don't quote me) with its quick movement back & forth, which might be the background. You might need to select the smallest focus area to achieve more reliable results.
  8. usayit

    usayit Mu-43 Hall of Famer

    My take on this.... Contrast AF (even in our OMD) has a long long long way to go before its up to par with phase when it comes to tracking moving objects. Of course, I don't expect the OMD to compete with my previous camera, the 1DmarkII, but this is one aspect of the system that does disappoint. (Totally happy with everything else).

    I'm still experimenting with various settings on the camera to see which gives me the best results. Some things that come to mind:

    * As an experiment, I turned off release priority (menu C.Release) while in constant AF mode, this will prevent the shutter from tripping when the camera has ~not~ acquired confirmed focus. Now experiment with a moving subject and notice the time between frames between actually frames exposed. Its long. That will give you an indication of the camera's ability to track subjects. What I have found is that slow moving subjects are ok... its when things are moving fast away or towards the photographer's position that it struggles. For those fast moving subjects, I generally switch to SAF and pump it (although I'm hoping to find a better way).

    * Ironically, I found CAF + TR mode pretty useful for static subjects. Makes it easy for the focus point to stay with the subject while I experiment with composition.

    * Under "J - Built in EVF", there is a setting for refresh rate. By default, its set to "normal". An article at preview claims that settings this to "high" (120hz) does improve AF performance. I'm still experimenting with this to see if that is truly the case. It is worth a shot. They do also claim that it hurts low light performance though... so I usually return it to normal for most other cases.

    * Old school photogs would focus ahead of the subject and trip as the subject enters into focus. I'm hoping to do the same but our native lenses aren't best at this.

    Good luck... I hope people follow up in this thread with what does and does not work for them.
    • Like Like x 1
  9. meyerweb

    meyerweb Mu-43 Hall of Famer Subscribing Member

    Sep 5, 2011
    Unfortunately, what really works for me when I have to shoot fast moving action is my EOS 50D and L lenses. CDAF just isn't there yet.
  10. shizlefonizle

    shizlefonizle Mu-43 Veteran

    Apr 21, 2012
    Like usayit said, turning off release priority can be a good solution. I turn it off all the time when shooting action (regardless of SAF or CAF). You might not get the shot when you want it, but you wont get a bunch of out of focus frames. If the shutter doesnt go down then release and press again till its in focus. I managed to get a lot more keepers this way.
  11. WT21

    WT21 Super Moderator Subscribing Member

    Feb 19, 2010
    Agreed with all here. You are getting missed-focus, not back focus.

    CDAF is not good for action shots.

    I usually focus on the ground where my subject is going to be, and either hold down the half-press to keep the AF, or flip it to MF and wait for the subject to get into the plane of focus. Also, keep the shutter speed up by using S or M modes.
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