Loosing focus in sequence shooting

[bwb kiteki]

Hey guys,

I was shooting kiteboarding recently, and once i uploaded the photos i noticed every now and then there was a shot which was out of focus?
Although the shot before and after was clear.

What is the reason for this and how can i fix it.

Camera: canon 40d
TV mode
6.5fps
Al servo

Thanks guys

 

[PhotoXopher]

Automatic servo, focus jumped.

That's my guess based on your info and no photos to look at.

 

[Overread20]

A limitation of AI servo and (possibly) your lens. Simply put the AI servo mode is not prefect and when under pressure with a fast moving subject and the fps of the camera it can end up not managing to lock onto focus when the frame is taken.
A good fast focusing lens along with a topend camera body (1D line) can get things near perfect - the rest of us have to do as best we can

 

[inTempus]

Yeah, the 40D really isn't designed to track fast moving objects. This is where Nikon and their D300 (and on up their product line) has the clear advantage. Well, that was until the 7D was announced. For Canon shooters you needed a 1D body to nail focus every time on fast moving subjects until we had the new 7D.

The 40D only has 9 AF points where as the 7D has 19 and the 1D has 45. The Nikon D300, D700 and D3 all have 51 points.

 

[Derrel]

7D, good autofocus? Read Rob Galbraith's comments on its AF: he has actually had the camera to shoot with. The system might be as bad as that in the 1D Mark III... early tests are not all that great sounding to me.

Here's what Rob wrote about the 7D,and note the high-end, 200mm f/2's very poor performance:

"Continuous focus using Spot AF, centre AF point, AI Servo and the EF 200mm f/2L IS, tracking a soccer player for a few minutes in fading light, the results showed promise but were ultimately inconclusive: through about 200 frames, the camera was able to hang onto focus properly for portions of several sequences, better than we've ever seen from the 50D, as well as deal with the AF point moving off the subject briefly. But it would also lose focus for several frames for no apparent reason, even when the AF point was right on the mark and the subject was moving at an easy pace."

"Continuous focus using Zone AF, nine points in the centre, AI Servo and the EF 200mm f/2L IS, tracking a running dog in fading light, the results were terrible. Over about 80 frames the camera got almost nothing usably in focus. If this result is representative of Zone AF, then Zone AF will be the way wrong choice for fast-moving subjects. We had better luck tracking the same dog with Spot AF."

Rob Galbraith DPI: Autofocus, video and more

Save the hype until more people can confirm this is a good-focusing action camera.

 

[table1349]

Most AF issues like you describe end up being user error. In AI servo, use only one focus point. The center point is usually the best. Keep the center point DEAD ON THE SUBJECT. That is where most errors occur. If that center focus point skips to the edge or off of the subject for even a fraction of a second the focus will change for what ever it is seeing at that fraction of a second.

Keep in mind that focus points are also relative. They are not exact in terms of size of the glowing point in the viewfinder and exact placement. Shooting a small target at a long distance where the focus point is bigger than the target will also result in the same issues. A little practice will up your keeper rate.

 

[Derrel]

Rob Galbraith is a former professional news and sports photographer,and has a staff of similar people who write for his web site. He does extensive,hands-on training for other full-time sports shooters and media photographers. The problems are hardware-related, not simple user error. The 1D Mark III autofocus fiasco has been a total disaster for Canon,and is one reason so many former Canon pros, like Robert Hanashiro and other shooters at USA today and Sports Illustrated, abandoned the 1D Mark III and went to the Nikon D3--better autofocusing and full-frame. Hanashiro mentioned that at the 2008 Olympics, "more than half" of the shooters there were using Nikon.

The 1D Mark III's 20 months of problems with autofocusing have cost Canon *dearly* SportsShooter.com - I am considering Making the Switch "Canon--->Nikon"

As Rob Galbraith wrote at the above URL: "The 7D represents Canon's most interesting attempt in awhile to provide working photographers with a camera that incorporates a useful complement of pro features at a midrange camera price. It's a trend they started with the EOS 20D back in 2004, but successors to that camera, including the current 50D, have been easily eclipsed in the last two years by the Nikon D300 (and its refined, video-capable replacement, the D300s). The 7D is Canon's response."

"An all-new AF system in the 7D that features 19 cross-type points (covering roughly the same frame area as the 50D's 9-point system), five distinct AF modes and clever AF configuration options."

"Put in charge of the 7D's development, however, we'd have chosen something like a 12MP sensor with better high ISO performance and richer low ISO files."

"Frame coverage for the AF sensor is similar to the 50D - it covers a fairly tight area in the centre of the frame, with minimal spacing between the AF points."

"There are other AF-related configuration options discussed in the next section. First, some observations about the camera's autofocus performance. We've been critical of Canon autofocus in recent times, starting with the AF problems of the EOS-1D Mark III in the spring of 2007 and continuing, with less severity, through to the EOS 40D and 50D, both of which struggle in continuous focus situations. []Rob Galbraith DPI: Page Not Found

"So, Canon's reputation as the maker of premium autofocus has been tarnished of late. Into that reality comes the 7D, outfitted with Canon's first all-new AF system in about two years, as well as its most full featured, exceeding in several respects that found in 1-series models."

Their conclusion: "The only open question is the AF system. All the options are there, and focus on static subjects was just about perfect with almost all lenses we tried. Continuous focus, which has been the albatross around Canon's neck since the EOS-1D Mark III hit the streets in 2007, is really the only area of the camera where a lot more testing is needed before we'd be comfortable talking about its suitability for peak action sports, not to mention using it ourselves for this purpose."

Galbraith and his staff of pro sports shooters have repeatedly wrote that the 40D and 50D are simply not capable cameras for continuous focusing for sports use. Rob Galbraith's web site is the one most US sports shooters look to for guidance and the honest reviews of new equipment. He still will not endorse the 7D for sports use, for himself,his staff,or others.

 

[musicaleCA]

I'm just glad that the 7D FINALLY has colour metering. Finally. I mean, seriously; took Canon long enough.

Another consideration is that Canon has a wider range that they consider to be acceptably in focus. Nikon's AF systems are much more stringent (used to be that Canon had a speed advantage because of it, but not anymore).

I got to hold a D300s today; sexy beast, if a little confusing to figure-out the Nikon controls for me.