Sports shooting in AF-C

Discussion in 'General Technical Discussion' started by ZBaum, Apr 11, 2007.

  1. ZBaum

    ZBaum Guest

    I'm looking at ways to improve my keeper percentage while shooting sports, and one thing that I noticed in my last outing is that many of my shots with my new lens (a Sigma 70-200 on my D70) are OOF. Granted, the light was pretty bad, and I've yet to use the lens to shoot sports under sunlight due to some horrible weather.

    Since I got my D70, I've always shot in Dynamic AF mode, and of course use AF-C on the center point for sports. I vaguely remember reading about someone who had trouble shooting moving objects using Dynamic mode, so I'm thinking of trying out Single Area mode. Is it possible that while using Dynamic AF that the camera is getting "confused" when there are many moving people in the frame? The camera/lens combo works very well while shooting stationary objects in AF-S mode with the aperture wide open, but I'd like to improve my output with moving objects.

    Exposures were all around 200mm, 1/400", f/2.8, ISO 1250-1600, so I don't think it was a problem with handholding. Motion blur also doesn't seem likely, as the subjects are "fuzzy" rather than "streaky". This leads me to the conclusion that I'm not hitting focus quite right in the first place. Any general suggestions or tips? Thanks a lot.
     
  2. InitialD

    InitialD

    151
    Mar 12, 2007
    Malaysia
    The CAM 900 on the D70 is a slow and it will be a hit / miss thing with sports especially if you're shooting in low light. It takes lots of practise. Yes, Dynamic AF is too much for the CAM 900 to follow. Stick with Single AF on the center bracket with AF-C. A monopod helps to alleviate the weight which would help you to concentrate on your subjects better.
     
  3. jaymc

    jaymc Guest

    This is from the Magic Lantern Guide for the D70:

    "Limitations of the AF System:
    - Low light
    - Low contrast
    - Highly reflective surface
    - Subject too small
    - Fine detail in AF bracket
    - Regular geometic patterns
    - High contrast within autofocus area"

    - Jay
     
  4. ZBaum

    ZBaum Guest

    Thanks for the comments. I know that the CAM 900 is limited, but I hadn't had too many problems in the past. I also know that the D70 has a tendency to backfocus with some lenses (it did it with the 18-70 I used to own, and it's possible it's also doing it with my 70-200). I'd love a better camera, but that's not going to happen for quite some time. Ah well....
     
  5. ZBaum

    ZBaum Guest

    Well, I shot again today when we had some nice sunlight. I shot with both my D70 & Sigma 70-200, and also with a D200 & Nikon 300 f/2.8 AF-I. The D200 photos came out awesome, while I got many more keepers with my D70. Both were on AF-C, still Dynamic Area. I think the problem during the last game was a lack of contrast/light. That said, the D70/70-200 combo did miss the focus a few times, but I think that I'm expecting too much out of that setup. I must say though, shooting with the D200 today has made me start thinking about trying to afford one....
     
  6. If you're shooting the 70-200 at 2.8 the DOF is pretty narrow. Could it be that with the better light you were shooting at a smaller aperture and thereby getting more keepers? Just a thought.
     
  7. Gale

    Gale

    978
    Jan 26, 2005
    Viera Fl
    Once shooting a D200...your hooked:>))))
    Boy what a difference ( in action especially)
     
  8. Hey, Zach!! I just saw your

    signature. I'm an RPI grad, BSME class of 1985.

    I shoot low light sports, generally ice skating. Up until January, the D70 was my camera and I have used both the Nikkor 80-200 f/2.8 and then the 70-200 VR. The problem with low light sports is that it is hard to get a good balance of the three variables that make a good exposure, namely aperture, shutter speed, and sensitivity (ISO). I have done a lot of experimentation and have found that the following works consistently best for me:

    Single focus area: use the thumb toggle to select the area you want in focus, don't let the camera decide what it thinks ought to be in focus. With practice, you can select a different focus area very quickly.

    Shoot manual mode and use Auto ISO.

    Set the max ISO to the largest value you are willing to live with. I use 1600, and it is often not quite high enough.

    Use the largest aperture you can get away with. I shoot f/2.8 for ice skating. As has been pointed out by another poster, the depth of field will be very thin (about 3 feet for many of my shots), but practice will show you how to keep the important part of subject where you want it. I try and get most of my shots where the subject is parallel to the image plane, that minimizes blurred areas.

    Select the minimum shutter you can tolerate. I would love to use 1/500, but usually have to shoot 1/320 or 1/250.

    I also switch between matrix metering and spot, depending upon my subject and background, and what I want properly exposed.

    I use pretty much default setting for other settings.

    A monopod will help greatly in giving you a stable shooting platform, and well-practiced technique will provide the highest percentage of keepers. One thing I tend to do is to follow my subject and pulse the shutter release to the half-way position. That allows me to have confidence that the focus will be close and hunting will be minimized.

    Here are a couple of samples of low light shots I have taken using the D70 and techniques I described (excuse me if you have seen any of these before):

    1/250s f/2.8 at 140.0mm ISO 1600
    original.

    1/320s f/2.8 at 34.0mm ISO 1600
    View attachment 90145

    and this even works for well-lit swimming:

    1/400s f/4.0 at 175.0mm ISO 400
    View attachment 90146
     
  9. ZBaum

    ZBaum Guest

    Thanks for the comments everyone. I think I'm having a little trouble with my Sigma 70-200, and that it's backfocusing a bit (or quite a bit, in some cases). I shot at f/2.8 during the night game, and then yesterday I shot at f/3.5, which I think was the difference. I'm seeing what it'll cost for Sigma to adjust it, but at this point, I might sell the lens and get a prime (180 or 85). Then I'll just use the newspaper's 80-200 AF-S for the next three years.

    Joe - Great to see another (former) member of the 'Tute here on the boards. I think there are three of us here. Goes to show me that engineers have nice toys to play with :biggrin:. Thanks for the examples and the tips, I'll remember to come back here in the future as a reference.
     
  10. There is a backfocus test document on my site -- feel free to download it and evaluate your lens' performance on your D70.
     
  11. ZBaum

    ZBaum Guest

    Ray - I've used that chart in the past, and also have one or two others that I've found. After reviewing some more shots, I think it's pretty obvious that it is backfocusing. It'd be one thing if it were only in one or two photos...but in almost every photo (I did get a few really sharp ones), the object/person I was focusing on is in front of the zone that's in focus. Thanks for suggestion.

    EDIT: Here's an example. Used AF-C on center point. First is the full scene, second is a center crop, third is a crop from the person standing in the back. Nearly every photo is like this, so I kind of doubt that I'm missing the focus, or that the lens just isn't sharp for some reason. In fact, the lens seems to be very sharp...it just can't focus where it should.

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited by a moderator: Apr 16, 2007
  12. gvk

    gvk

    388
    Jun 17, 2005
    Mystic, CT
    Your lens may well be back focusing. However, it is difficult to tell if that was the problem from the shot you posted. You say that you used the center focus point. Unless you focused and recomposed, the center focus sensor pointed at the dark shirt with very little detail or contrast for AF to lock on. Even if you focused on the singer's face and recomposed, then it is likely that AF still would have locked on the bright arm and guitar due the much higher contrast. On every Nikon DSLR that I have used, the actual focus sensor is considerably larger than the bracket shown in the viewfinder, and AF usually locks on the highest contrast region within the sensitivity of the sensor. Manual focus is often best for this type of situation. Check the camera manual a list of situations where AF has problems. This scene exhibits two of these problem areas (low subject contrast and sharply contrasting brighness nearby).
     
  13. ZBaum

    ZBaum Guest

    Alright, here's a better example (center point again, right in the middle of the girl's face). I would assume that the camera would use the line that her hair makes on her face, as it's a pretty contrasty line. But again, the people behind her are in focus:

    [​IMG]

    [​IMG]

    [​IMG]

    Even the girl's face that's two rows back is sharper :confused:
     
  14. That doesn't look great... I'd still try the chart to know for certain, but it doesn't bode well for your lens.
     
  15. Zach;

    You might try shooting something outside in good light that is stationary or slow moving. Mount the camera on a tripod or at least a monopod. Shoot at f/5.6 or 8 and see what you get.

    If the lens is indeed bad, do you have the option of returning it at this point? I remember you saying you'd investigate the cost of getting it calibrated by Sigma. Any word on that? Good luck and keep us posted.
     
  16. ZBaum

    ZBaum Guest

    Will do once I get a free moment from school/newspaper work.

    Brian - By shooting at f/5.6 or f/8, wouldn't I somewhat defeat the purpose? By f/8 there's more than enough DOF to put the subject in focus, even if the sharpest point isn't on the subject. Haven't gotten a chance to contact Sigma yet. I did contact the person I bought the lens from (someone here at NC). It took about 10 days between when I got the lens, and when I was able to fully test it due to poor weather and school work. I was informed that I can't return it. I already stretched my budget well past what it should've been, so it looks like I'll be selling it if it is indeed backfocusing. Thanks for the comments and suggestions.
     
  17. Good point, I hadn't thought that through very thoroughly.

    Did the seller indicate if s/he had the focus trouble you're experiencing? Hope you can get it figured out.
     
  18. ZBaum

    ZBaum Guest

    I was told that it worked perfectly, and that it is an extremely sharp copy of the lens. I have no doubts that it's very sharp...it's just that focus never hits where it should. I've had more success with an old Nikon 80-200 push-pull, and that's a screw-driven lens. Something tells me the HSM should outperform it.
     
  19. J.Alan thanks for all the tips as well. This was exactly what I've been looking for recently as I'm still not happy with with my low-light action photography.
     
  20. ZBaum

    ZBaum Guest

    Off to eBay it goes...
     
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