Dynamic v Single Area AF - still not gettin' it

Discussion in 'Sports Photography' started by Dennis Carter, Aug 12, 2008.

  1. Dennis Carter

    Dennis Carter

    Jun 29, 2007
    USA
    Which mode would you use if trying to frame the 2 following shots and why?

    For 1, I've been thinking/using Dynamic Area. That is, place a sensor on the player and if the AF detects movement, the focusing sensor will hopefully change to a different sensor attempting to keep the player in focus. Of course, the sensors on my D1H have quite a gap and that may be a problem compared to what CAM3500 offers.

    For 2, Single Area. Put the middle sensor on the center of mass and have enough DOF to allow the face to be in focus.

    I ask because of a discussion on another board suggesting I have it totally [email protected]

    #1

    2756947756_363c042d94_o.png

    #2

    View attachment 238886
     
  2. Tim White

    Tim White Guest

    IMHO, Dynamic Area is only useful if you have a lot of available sensors near the chosen one, ie, if you have the new 52-point AF system. If not, I'd use Single Area.

    Re: #2, why not focus on the face with an ideal aperture value instead of focusing on the center of mass and using a compromise DOF setting to hopefully get the face in focus? :confused:
     
  3. Dennis,

    This probably doesn't help, but I think it is one of those choices we make, none of which are all absolutely perfect in all situations.

    For example, in number 2, Dynamic area, where the camera chooses the sensor, it could lock on the right hand of the player out of frame, rendering the centre player OOF, depending on the DOF. But if you want a blurred background, you could be forced to choose a larger aperture, which results in shallower depth of field. With #1, you could get the right leg in focus (which has happened to me with both Dynamic and Single BTW).

    On my D200, which has fewer sensors that are wider apart than the D300, I use Single Area for sports and I choose, right or wrong, the focus point, instead of the camera. I have, and do change the sensor manually, and I have also used a group of sensors (for example to keep the catcher in focus when the batter is in the frame) but the key element IMHO, is that the photographer should choose, not the camera.

    It's not that the camera is necessarily wrong, it does what we tell it, but it's choices might not be my choices. JMHO.
     
  4. I haven't been happy w/ Dynamic, so I just shoot single pt, and put my focus point on the face, regardless of aperture. Def makes it harder to track the subject, but w/ the add'l cross hatch sensors (15) on the D300, it's a lot easier to select one off center, for example, if I'm in portrait mode. I think if I was tracking a racecar, I might find Dynamic a better method. But w/ these sports (LAX, soccer, basketball, etc, there are just too many things flying around the frame to confuse the AF system..JMHO)
     
  5. I went out yesterday to shoot the racing greyhounds and changed from single point to dynamic 9pt. While i did get a better % in focus with the 9pt. the trade off was that I did not get that pin point, spot on focus that I get with single point.

    Because Im striving for the best IQ possible, I will glady switch back to spot single point focus because even though I may get a few less in focus, the ones I do get are of better IQ. (Also, no one but my wife and I usually see my throw outs anyway!!:wink:)


    take care,

    Rick
     
  6. Dennis Carter

    Dennis Carter

    Jun 29, 2007
    USA
    Ok, a TIGHT cluster of sensors makes sense to me. If the selected sensor slips off your target, then there are other sensors nearby to pick up the target again. At least, I suppose that is how it's supposed to work.


    If the target is moving erratically, then it's sometimes easier to keep a sensor on the center of mass (which is a larger target) rather than the face. Of course, perhaps I just need more practice! :biggrin:


    Now, having said all that, Mark, Chris and Rick, I kinda hafta agree with what I think you're saying. Just use Single Area AF and maintain control of your photography. Hmmmmm....so why are we paying for all this fancy schmancy AF?

    I'm sure I'm missing something, but what do I know? I'm just an ol' dad with a camera.
     
  7. Dennis,

    On the plus side the accuracy and speed is much better today than it was not so many years ago. In some or many cases, I don't think it's so much that the AF system got it wrong, it's just that there is only so many inches in the field of focus.

    For example, this one that got away::eek::redface:

    101570739.jpg

    Thank goodness his gloves were clean, for once.
     
  8. Question for you folks:

    I like to use zone or "pre" focusing when shooting the greyhounds in the turns. Im not sure what it is but heres what I do:

    Focus on a spot where I think the dogs will be in the turn before they get there. I then press and hold the AE-L/AF-L button down to lock in the focus. As soon as the greyhounds get close I start shooting at 8fps and see what happens!

    When using this technique is it relavent which type of AF-Area Mode is being used or if you use single point focusing? The reason I ask is because the way I understand it if you choose say 9pt., then while you are focusing on the piece of dirt or spot on the track the AF system will determine the focal point that has the most contrast within the 9 applicable points and use that one to focus. As soon as you press the AF-L button you have locked in that focus with that focus point and it will not change until the button is released and recomposing is done. If that is true then it would seem to me that there would be no difference between 9pt. and single point AFTER THE AF-LOCK button has been pressed. Does that sound correct?

    Ok, to further confuse me.......yesterday at the track when I switched from a successful combination of single point zone focusing with no VR to 9 pt. with VR my images werent as sharp (why did I switch....because I just have to tinker and Im a dummy!!!). So, do you think it was because of the switch or maybe I just didnt nail the shots and the single point vs. 9pt. factor just wasnt a factor?

    Sorry to ramble, let me know your thoughts!

    my best to you,

    Rick
     
  9. Rick,

    I'm not to familiar with the D300, this where Thom Hogan's guide would come in handy. On the D200, the type of focus and movement could cause the focus point to move on the second shot, depending on how your camera is set up.

    Having said that, I would tend to agree with you that once you set and lock focus, for the first shot it doesn't matter, it's the next shot in the burst that could be affected by movement. Again, if there are a lot of things for the sensor to grab for focus, it will.

    In your case, why not focus on the spot, knowing that your zone of focus or DOF will be say 4 feet deep. Then switch to manual focus, which effectively locks the focus for an entire burst.

    As to VR, the rule of thumb as I understand is to use it below 1/1000 (which is also roughly the length of time it takes to settle in and the 'frequency' that VR works at) turn it off above that. Some have no issues above 1/1000, some do. Plus it's also possible you didn't nail it. It happens so I understand.
     
  10. hey Rick, my understanding is that's what the AF-ON button is better suited for. If you focus say, on a fence post and press and release AF-ON (provided CSM A5 is set to OFF) it will lock the focus until you press it again/trip the shutter. If you continuously hold the AF-ON button (and while you're in AF-C) it will continuously reacquire focus. I have my AE-L/AF-L button set to AE only (tripped when I hit the shutter).


    Not certain about your second question. My first thought is that you'd want to be in single. Dynamic works such that you choose the initial focus point and then the camera tracks it, using other focus points (automatically) to maintain focus. Thus, if you've pre-focused on a spot, vs a dog, it may be difficult. Again, I'm probably wrong, let's see what the cognoscenti say.