D2h/x AF question

Discussion in 'General Technical Discussion' started by jklofft, Sep 8, 2005.

  1. When the camera is in AF-S AF (assuming the default focus priority) mode and the frame advance is set to CL or CH, does the AF system refocus between frames on not?
    Similiarly in AF-C (assuming the default release priority) mode does it refocus between frames?
     
  2. ckdamascus

    ckdamascus

    928
    May 14, 2005
    New Jersey
    Based on my correspondence with Thomas Hogan, I would assume it does refocus.

    "Yes, there is much more to autofocus than mere focus drive speed (which only applies to non AF-S lenses, by the way). The biggest advantage a D2 series camera has over the D70 is the mirror blackout time (the autofocus sensors live below the mirror and require the secondary mirror to be in position to deliver data to the camera). The viewfinder blackout on a D2h is so short that you can actually follow action at 8 fps--you'll lose the subject (and possibly focus) on a D70 at 3 fps." -- Thomas Hogan

    Based on that article, with AF-C, the camera does predictive tracking during the black out period.

    So, my summary would be, the camera has to refocus because you just closed it's eyes (by depressing the shutter). AF-C lets it visually "guess" where it is while it's eyes are closed. AF-S focuses on what it last saw.

    In either event, after it's eyes open back up (the viewfinder blackout time), it has to refocus. This is what makes the D2H such a great action camera even though it DOES NOT HAVE SOUPED UP BODY MOTORS like many would like for you to believe. The D2H has a better tracking mechanism, which isn't quite the same as faster body motors.

    "Only the F5 (and I think some of the D1 series) had the souped up body motors.
    " -- Thomas Hogan

    That was in response to my email
    "During my Sigma vs Nikon lens test, I wanted to see which would focus faster. I tried a primitive stop-watch setup and it appeared the Sigma was maybe 0.1-0.2 seconds faster. It's hard to quantify but it felt a tiny bit faster.

    However, I decided to see how much slower it was with the D70 instead of my D2H.

    The scary thing was the results were nearly identical between the bodies!

    I switched to manual focus to focus at 1.5 meters for an object at infinity. Then I switched to manual focus and hit the clock as I pressed the shutter. Once I got a lock on, I stopped the watch at the same time.

    I'm surprised, as I was under the impression the D2H had super motors to speed up AF."
     
  3. JeffKohn

    JeffKohn

    Apr 21, 2005
    Houston, TX
    My experience is that when using continuous drive, the camera will re-focus in-between shots even on AF-S. This sucks if you focus/recompose, because only the first shot will have the focus point where you wanted it. That's one reason I use the AF-ON button for focusing and not the shutter release.
     
  4. Every time you press the shutter, the camera resets. It doesn't continue anything from frame to frame, it does a full operation per frame. However, when you're shooting high speed continuous, the focusing mechanism doesn't usually have to move much because assuming you're shooting the same object, the lens will already be focused at the point of location from the last frame. 8FPS is pretty fast, so it's not like the focus gets reset, it just refocuses from the last point when the shutter was released.

    If you're finding some of your shots out of focus, (or your continuous speed slowing down) I would suggest trying one of a few things (or combination of):

    Disable a4 in custom settings menu: Lock-On
    I *think* thats a4. Depending on what youre actually shooting, Lock-On might slow down your focussing process as it tries to verify which object is your main subject.

    Change between Single Servo AF and Continous AF (one might work better, I typically use Continuous when Im shooting moving objects).

    Use one of the Group Dynamic AF modes. Set Group Dynamic on the camera body, then go into Custom Settings Menu and try either Pattern 1/Center or Pattern 2/Center. This should allow the camera to intelligently track movement from where your aiming, without having the overhead of all 11 sensors to process for focus tracking every time you release the shutter.

    These suggestions aren't really about continuous frame shooting, but they should streamline the full process of what has to happen between every single frame. You might get more out of focus shots or slower FPS rates if youre camera is just trying to do more than it has to each time you press the shutter.
     
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