Help! Question...

I put this question in another area, so I was told to try this one. I have a Canon XTi ten megapixel camera. I am having problems with the focus. In the automatic settings on continuous shooting one pic will be clear and the next blurry. It has been doing this even in a setting of just taking pics of my grandson. One will be great then blurry. If I use the manual focus mode to shoot they are fine, but that doesn't work in a sports setting or when i want to capture shots quickly. I have checked the AF setting and it is in AI mode, but in the other settings it is automatic and I can't adjust the AF. I have had this camera for at least 5 years. It used to take these pics great and I am thinking the body is worn out and the lenses are working fine. I want to upgrade, but I want to make sure that it isn't anything I am doing wrong. I know that my camera didn't do this before. Thanks for any help you can give me.

So, it sounds to me like the AF system is "hunting" for correct focus. This happens sometimes under low-light conditions, or if your subject is very dark. Also happens if you are trying to focus on a subject that is closer than the specification of that lens.

I was at a football game shooting my granddaughters in peewee cheer. i was using a telephoto lens and it was under stadium lights. But sometimes it does it in my home which is darker. You may be onto something. I"m not sure what to do to fix the problem, but I will be more aware of the differences of the light. That may help. Thanks. I was afraid my camera was wearing out. LOL

In a case like this, I recommend that you start out setting the camera to Servo AF and nothing else. This implies that you need to use a mode like Av or something, as the AF mode can't be adjusted in the preprogrammed modes. Which is yet another good reason never to use them. Open the aperture as much as possible with your lens, then set an ISO value which gives you reasonable exposure times.

Then you select the center point on your 400D, since that's the only cross-type AF point that camera has. Thus it has the highest probability of being able to track your subject. Now aim for the subject, half-press the shutter button, track the subject, press fully to take a picture, return to half-press and keep on tracking.

To make this easier it's possible to set the camera to AF on the * button instead of half-press. Since it's easier to keep a button fully pressed than halfway, it accomplishes the same task in a way that's just easier to manage.

Good suggestions so far...I have one more:

Does this camera have "AI Focus" mode?...If so, use "AI Servo" mode instead.
As Anders said, you'll have to be in P, Av, Tv or M shooting mode in order to change the AF mode.

AI Focus starts in One Shot then switches to AI Servo if it detects trackable motion.

If you focus on the child in one position and she suddenly moves to a different position, sometimes AI Focus is too slow in changing to AI Servo to keep up...This could cause the scenario that you descibe above.

Using AI Servo AF mode with Back Button focusing, as Anders suggested above, will likely solve your problem, although inadequate lighting, as TustinMike suggested, will still cause AF problems.

thanks for all the help, I will try all those things. I haven't used the AI Servo, but I will try that and also in the creative modes. I have a soccer game coming up with a grand and want to get as much of the action as possible. Thank you for the great information. It is such a great help to me.

If you set the camera to the "Sports" scene mode, I believe it uses AI Servo focus mode. The scene modes are simply a highly automated modes that select many things for you, overriding or blocking out options that the designers of the camera have decided you don't need for that particular type of shooting.

If you set to M or Manual (same dial as the Sports scene mode), that's a manual exposre mode and unrelated to focus. Not recommended unless you know how to set up all the exposure factors.

Try using Av, Tv or P instead. These are still automatic exposure modes, but they let you set up the focus and other factors more to your liking. A lot of times people use Tv for sports... with that you can choose the shutter speed needed to stop the action, then just need to watch that the aperture is adequate (it will flash if underexposing, in which case you need to increase ISO).

AI Servo focus mode is what you need to use with moving subjects. One Shot is for stationary subjects. And AI Focus isn't really a mode at all, it's more automation that supposed to decide for you whether or not the subject is moving, then use the apprpopriate focus mode. You'll have much better success choosing for yourself.

What lens you are using is another big factor... Focus speed, accuracy and performance is a combination of factors of lens, camera and proper setup of both by the user. Canon USM lenses or Sigma HSM and Tamron's new USD are all faster, more accurate, generally speaking. Larger aperture lenses (up to a point) tend to be faster focusing too, simply because they provide more light for the AF system to work with.

Things that effect focus performance that are generally out of your control include the existing lighting and subject contrast. Low light and low contrast are both more challenging to the AF system. It will work more slowly. At those times your camera & lens might hunt trying to achieve focus.

Try manually selecting the AF point yourself... and choosing only the center one. You'll need to keep it right on the subject while tracking moving subjects in AI Servo, but it's the most sensitive and fastest acting sensor in your camera. You have to maintain half-press of the shutter release button continuously, as long as you want the camera to keep updating focus to the subject. Since focus is continuous and doesn't lock, there won't be any form of Focus Confirmation while shootin in AI Servo.

A special technique a lot of sports shooters use is called Back Button Focusing. You don't have to use it, but might want to give it a try some time.

When using AI Servo and tracking subjects, try to pick up your subject in advance and follow them for a while with AF activated and working, before taking the shot. You can continue to follow them keeping the shutter button half-pressed and taking more shots when you wish. If using a zoom, cradle the lens in your left hand so you can change the focal length at the same time, to reframe as the subject comes closer or moves farther away. I suggest framing tightly, but not too tightly when using only the center AF point. That allows you a little room to re-crop the image after the fact, if you don't always want the subject centered.

It takes some concentration to keep the active AF point right on the subject and some practice to get good using AI Servo. You'll likely see more missed focus shots at first and then get better at it over time. Skill levels also improve as you become more familiar with a particular sport, know what to expect and can anticipate the action. Still, there will always be a few missed focus shots, with any camera and no matter how much you practice. It's just to be expected... subjects change speed or change direction unexpectedly, fooling the camera's AF system, or we just happen to trip the shutter at the exact wrong moment when the camera is still refocusing. There are just too many variables to expect perfection. But using the right focus mode with good lenses and in reasonably good light, with practice and experience you should be able to get 80 or 90% of your shots acceptibly in focus. I consistently get better than 95%.