Road Train !!!!!!!!!!

by Russell McMahon

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I'm currently using a Nikon 28-200mm AF-D with my D7000. While trying to take action shots (e.g. my dog running or sports) none of the shots seem to be in focus even on AF-C mode. Would this be a limitation of my lens, or the body?

I tried to focus from the minimum focus distance to infinity and it took about ~0.5 seconds, so I'm assuming my lens isn't able to keep up with the subject which in motion.

I was wondering what you guys think the issue is and how I would be able to get sharper action shorts while shooting 6fps.

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Are you using 3D tracking? –  MikeW Mar 2 '13 at 20:20
1  
What shutter-speeds do you get? –  Itai Mar 2 '13 at 23:32
    
Yes, I did set it to 3-D tracking and I set my ISO such that my shutter speeds are around 1/120s. Perhaps I need a faster lens to compose these shots? –  Davy Li Mar 2 '13 at 23:50
    
1/120 is nowhere near fast enough to freeze motion. See Michael Clark's answer. –  ElendilTheTall Mar 3 '13 at 18:15

5 Answers 5

up vote 3 down vote accepted

There are two issues that are probably affecting your results. Your lens is fairly weak in both areas.

  • Auto Focus speed and accuracy
  • Camera and/or subject movement

The size of a lens' maximum aperture affects the camera's Auto Focus performance. Not only because the AF system has more light to work with when using a lens with a wider aperture, but also because of the physics involved and the use of edge rays by phase detection AF systems. In general, the same camera with a "faster" lens (one with a wider maximum aperture) can focus more quickly and more accurately than with a "slower" lens. Regardless of what aperture is set in camera, focusing is normally done with the lens wide open. The lens is then stopped down just prior to the shutter opening. Performance of the motor driving the lens' focus elements, including the gearing in the lens, also plays a part.

I'm not familiar with the D7000's available options, but most DSLRs in this class allow you to customize how the Continuous Servo AF works. Through the custom menus you can tell it whether to place priority on focus speed (at the expense of accuracy) or accuracy (at the expense of speed). When shooting continuous bursts you can usually tell it to prioritize one way for the initial shot and then shift to another priority for the subsequent frames in the burst.

The rule of thumb for preventing blur due to camera shake is to use a shutter speed no slower than 1/equivalent focal length. In the case of your APS-C D7000, that means 1/1.5 X the focal length used. At the 28mm end you could use a shutter speed as slow as 1/40 sec if you are practicing good camera stabilization techniques when shooting. On the telephoto end you need a shutter speed of 1/300 sec or faster. Image stabilization would help prevent blur due to camera shake, but your lens doesn't have it. In the case of shooting fast moving subjects like your dog, it makes no difference anyway.

To stop motion of fast moving subjects like a dog or athletes in motion you need faster shutter speeds. Shooting football from the sidelines with a 200mm lens requires about 1/500 sec or faster to freeze the motion. The closer the action is to you, the faster the shutter speed that you need. The only way to get faster shutter speeds in the same amount of light is to either raise the ISO or open the aperture wider. If your aperture is already wide open, then higher ISO is the only way to increase the shutter speed. The problem with higher ISO is that the increased noise (and the effects of using aggressive Noise Reduction) will reduce the amount of detail in the image.

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As Tony said, blur and focus are usually two different subjects. Blur is where things move too fast or the camera moved during exposure. Focus is the subject of the photo not being sharp.

As Itai wrote about, because you mentioned your dog running, I'm going to start off with your issue being shutter speed.

Coming from just shooting an indoor dog sporting event, I pushed my D7000 to (what I consider to be) its limit for both high ISO and autofocus performance and walked away with about a 30-40 percent success rate.

With trying to keep ISO as low as possible, because of the such poor indoor lighting, I first TRIED to shoot at a shutter speed of 1/320 to 1/500, at f/2.8. This simply isn't fast enough shutter to freeze much movement. At 1/500 I was barely able to freeze the fast moving dogs.

I ended up doing two things before I was able to get my shutter speed up to 1/800 - 1/1000 and started getting non-blurry images that were not underexposed:

  1. Bump the ISO up to 3200
  2. Switch from my f/2.8 zooms to an 85mm f/1.8 and shot it wide open

Because of the such shallow depth of field at f/1.8, I still missed focus on some shots, but the parts of the dog that were in focus (e.g. their tail), had very little to no blurring.

Now, onto the issue of focus.

What really helped me here was knowing the different autofocus modes of the D7000. The setting that gave me the best results for the conditions I was in at the time was continuous AF setting and the 3D autofocus mode with the main autofocus point moved 3-4 spots to the right. This let me get initial lock on the dog's head as it moved from my right to left. And, as I was panning the camera, the D7000 automatically moved the focus point to the left, keeping the dog's head in focus.

The explanation of all the autofocus modes in the D7000 manual is pretty much non-existant. To fully understand how all of the autofocus modes function, I highly recommend the following PDF:

Nikon D7000 Autofocus System Explained: www.pixelfinesse.com/_docs/D7000_AF_Explained.pdf

This document goes into great detail about each mode, scenarios when to use them and includes screenshots of the settings.

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how blurry is blurry ? Focus is one aspect, and you may be lens limited. But you can help the lens but only using the centre focus point - it is the most sensitive and by keeping this on the subject it will help.

I'm a canon driver so forgive me a little bit, but if the lens has stabilisation make sure its on the right setting.

Also, things that are moving, well move! So yo need to keep the shutter speed really high to freeze motion and keep things really Sharp. Or go slow and make the motion part of the composition.

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Actually, lens stabilization does very little for sports shooting. It stabilizes the camera/lens combination. But for sports, its the subject that is moving. –  Pat Farrell Mar 4 '13 at 3:15
    
I agree, but some lens do have a 'panning' function (canon EF L 300F4 for example) that stabilise in one plane only. IF this is the case it is either worth moving onto this function or turning it off completely. –  Tony Mar 4 '13 at 20:40

The 1/120s is certainly your problem. This is a speed used for relatively still subjects and person or animal moving would appear blurry at that speed.

To freeze the motion of something you need a fast enough shutter-speed. For someone running - I assume a dog can run around the same speed as a person - I would advise closer to 1/1000s for movement parallel to the focus plane and at least 1/500s if perpendicular to the focus plane.

You also need at the very least - even for still subjects - a shutter-speed of 1 over the effective focal-length of your lens when shooting without stabilization in order to get a sharp image. At the 200mm end, which is equivalent to 300mm, you would therefore need at least 1/300s.

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I've never seen a dog that couldn't outrun a person without raising any effort. So the OP needs a much faster shutter speed. –  Pat Farrell Mar 4 '13 at 3:16

Indeed your shutter speed should be bumped up, another thing you might want to check out is your `focus tracking with lock-on´ setting which controls the amount of time before the camera refocuses on a moving subject.

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