That's an open ended question without a lot of details to narrow it down (what type of sports, conditions - indoor, outdoor, night, if you use lighting, how close you can get, etc).
The safe answer would be: you can't go wrong with just about any of the 70 - 200 lenses. Whether or not you need the 2.8 is always a good debate, as is image stabilization. All 4 of Canon's 70 - 200 have attributes that make them shine in one way or another relative to the others, and they're all good all-around telephotos in general. You can't go wrong with having one in your quiver.
Another answer would be: you can shoot sports with any lens. Though in general sports photogs are always trying to get more reach, and more light.
Thanks, that helps. Is it daytime softball? You shouldn’t have difficulty shooting softball with a 50D and a 70-200 2.8 unless it’s really cloudy and dark. Under lights is different, and I’d do what I describe above. Have a look at these blurry shots you took, what shutter speeds are being used? And which shooting mode?
A couple of other tips worth mentioning. Set the AF system to AI Servo for moving targets & some people find it helpful to use just the center AF point & try their very best to keep it on one spot of the person they are trying to capture as the center of the frame. This helps perfect a smooth pan.
This is what I'm thinking. The 70-200 f/2.8 is an EXCELLENT lens.
Inspect the exposure info on your shots which are blurry -- specifically looking at shutter speed. For action photography, you want a MINIMUM of 1/250th and only slow-ish action will freeze still at that speed. For faster action you need to be at 1/500th or faster. It'd be especially great if you were shooting at speeds closer to 1/1000th.
Do be sure you are using the correct focus method. "One Shot" mode tells the camera to focus the lens ONLY UNTIL it confirms that it has properly focused at least one point. At this point the focus system is switched off and the camera waits for you to take the shot. This is great for non-action photography, but in action photography the subject is still moving... your subject may no longer be at that focused distance anymore. Using "AI Servo" focus method tells the camera to continuously keep checking and adjusting focus because the lens-to-subject distance is expected to keep changing.
BUT... there is a caution when using "AI Servo" mode. When you use "One Shot" mode, the camera uses a feature called "Focus Priority". That means that when you fully press the shutter button, the camera's priority is to guarantee focus. The camera will actually REFUSE to take the shot until it can confirm that it was able to lock focus on at least one focus point. When you use "AI Servo" mode, the camera switches to something called "Release Priority". Release Priority mode says that when you fully press the shutter button, the camera's priority is to guarantee that it takes the shot RIGHT NOW. It will do so whether the shot was in focus or not! So that's a very important distanction. You'll want to half-squeeze the shutter and make sure you've actually achieved focus before you press the button the rest of the way and take the shot.
If you are outside during the day and it's full sun, then you should be able to shoot at an equivalent exposure based on the sunny 16 rule. That is f/16 and set the shutter speed to the inverse of the ISO. At ISO 100 you can use 1/100th sec. But that's too slow for sports. You could use f/8 and 1/400th (just barely fast enough to freeze most action), or bump the ISO to 200 and shoot at f/8 and 1/800th. Note that this is for "full" sun. If it's light or moderate overcast then you you'll likely need an extra stop or two worth of light. You could take the f-stop down to f/5.6 or even f/4.
I'm suggesting f-stops that broaden the depth of field to help with focus, but you'll get more light (albeit with a slightly narrower depth of field) by going to lower f-stops (e.g. f/4 or f/2.8).
There is some advice about "panning" in this thread. Keep in mind that panning is something that takes practice. When panning, you are deliberately using a shutter speed which you know is not fast enough to freeze action. But you make sure the lens follows the subject as smoothly as possible. This causes the subject to hopefully be fairly sharp (moving body extremeties such as legs and hands may be blurred but this is often acceptable... the main part of a persons body as well as their head (parts that don't move so quickly as the extremeties) will usually be pretty good). The background, however, WILL be blurred with motion. This creates some drama in the photo because it's a way to take a "still" photo and yet still imply the sense of motion and speed. The import take-away for you is... it takes practice.
Put the camera into continuous shooting mode. Also if you normally shoot RAW, keep in mind that this is a situation where you may want to switch to JPEG. The camera can shoot far more JPEGs before the internal buffer fills up, but of course you don't retain as much data in a JPEG and will sacrifice adjustment latitude. When shooting panning shots, you'll find that if you take a continuous burst of shots, that some of them will be noticeably better than others. The same is true of action shots in general.
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