Canon 450D autofocus problems

I shoot a lot of outdoor portraits with my Canon 450D (Rebel XSi) and Canon 70-200 f4L IS USM and the results are very nice when the focus is right on.

But only 20 to 40% of my shots are tack sharp, most of the time when my subject is not moving. The action shots and kids portraits are generally oof by a little bit.

I am convinced that my techique is good because I never shoot with the 9 focus points on auto, I'm always selecting one of the spots.

I've also read that you could calibrate your lense(s) but it is not available on the 450D. I'm also planning to uprgade to a 5DIII when the 5DIV comes out, but until then (october I guess?) what do you recommend me to do to improve my AF accuracy?

Thanks in advance.

Marc dbr wrote:

I shoot a lot of outdoor portraits with my Canon 450D (Rebel XSi) and Canon 70-200 f4L IS USM and the results are very nice when the focus is right on.

But only 20 to 40% of my shots are tack sharp, most of the time when my subject is not moving. The action shots and kids portraits are generally oof by a little bit.

I am convinced that my techique is good because I never shoot with the 9 focus points on auto, I'm always selecting one of the spots.

With moving subjects do you have the AF mode set to AI Servo? Are you allowing it to track your intended subject by holding at half-press for a moment or two before full press to capture? And/or do you have the Drive set to Continuous and capture a burst to give the camera time to "catch up" to your moving subject since it continues to track between shots of a burst?

I've also read that you could calibrate your lense(s) but it is not available on the 450D. I'm also planning to uprgade to a 5DIII when the 5DIV comes out, but until then (october I guess?) what do you recommend me to do to improve my AF accuracy?

The 450D does not have MicroFocusAdjustment, but you can have your lenses and/or body calibrated by Canon Service (or other shop) if that's the problem.  But since you get good AF with still subjects I doubt it's lens calibration causing the issue with moving subjects.

Thanks in advance.

When I shoot portraits where my subject isn't moving I have my focus mode set to "one shot", when I shoot kids portraits and action I have it set to "AI Focus" and when I shoot something like a soccer game I have it on "AI servo".

I think that my 450D needs calibration though because even when I'm in "one shot" single point AF, with still subjects, the eyes of the subject can be slightly out of focus. I have to say that when my subject is not moving, I have the best chance to get a sharp image

Thanks for the advice Olga, I was not aware that the center one was the only cross type.

I am definitely going to use that single AF point from now on.

Marc dbr wrote:

When I shoot portraits where my subject isn't moving I have my focus mode set to "one shot", when I shoot kids portraits and action I have it set to "AI Focus" and when I shoot something like a soccer game I have it on "AI servo".

You only need One-shot for a few specific purposes (mainly to be able focus then recompose). In all other cases where you can keep an AF point where you want it on the subject, Servo is better. (I know that's not what it says in your camera manual, but the recommendations there are variously vague, simplistic, ambiguous, and misleading. You can do better.) "Nobody" recommends AI Focus.

I think that my 450D needs calibration though because even when I'm in "one shot" single point AF, with still subjects, the eyes of the subject can be slightly out of focus. I have to say that when my subject is not moving, I have the best chance to get a sharp image

I wouldn't jump to that conclusion. There are other things that can cause blur that's easy to mistake for a focus problem. Tell us more about your settings (filter? shutter?...), technique (how you're holding and/or supporting the camera, how you frame the shot, how you press the shutter button...), and post an image with full EXIF that shows the problem, and we might be able to spot something.

I've had great results with AI Servo and Back Button focus on my 450D. I used to always use One Shot focus with half-pressed shutter but there would be quite a few where the focus missed, even for static shots. I was quite surprised to get better results with AI Servo and Back Button focus.

It's really the best of both worlds, and I only use the centre point.

Just keep holding the back button down if you want continuous AI Servo focus.  And you can keep holding it whilst you fire the shutter.

If you want one shot focus, just press the back button for half a second and release.  This works for the Focus-recompose technique.  You can also press the back button several times just to be doubly sure of the focus.

I got good results shooting a soccer match and also my 2 year old daughter who always tries to run away whenever I point the camera at her...GRRRR!

(To set back button focus: Go to Custom Function 10 and select option 1.)

(User Manual Pg158.)

PhilPreston3072 wrote:

I've had great results with AI Servo and Back Button focus on my 450D. I used to always use One Shot focus with half-pressed shutter but there would be quite a few where the focus missed, even for static shots. I was quite surprised to get better results with AI Servo and Back Button focus.

It's really the best of both worlds, and I only use the centre point.

Just keep holding the back button down if you want continuous AI Servo focus. And you can keep holding it whilst you fire the shutter.

If you want one shot focus, just press the back button for half a second and release. This works for the Focus-recompose technique. You can also press the back button several times just to be doubly sure of the focus.

I got good results shooting a soccer match and also my 2 year old daughter who always tries to run away whenever I point the camera at her...GRRRR!

(To set back button focus: Go to Custom Function 10 and select option 1.)

(User Manual Pg158.)

+1 This is exactly how I shoot too.  Extremely versatile.

R2

Thanks for the advice, I'll try it out and we'll see if it works for me

I'm not using any filter on my lens, and because I always shoot outdoors I keep my ISO around 100-200 and my shutter speed at 1/125 or above. I'm holding the Camera correctly (left hand supporting the lens) with IS turned on. When my subject is not moving I focus, then recompose and shoot. Otherwise I focus and shoot quickly after focus archievement.

so I think I'm not doing anything wrong

Marc dbr wrote:

But only 20 to 40% of my shots are tack sharp, most of the time when my subject is not moving. The action shots and kids portraits are generally oof by a little bit.

One thing to check would be the AF sensors at the bottom of the mirror box.  Make sure they are absolutely clear.

R2