very simple focus questions

What am I doing wrong?

1.When I take a picture, what I want appears to be in focus, however when I look back at the picture on the camera, what I wanted in focus is not in focus. I know the cameras have a hard time focusing in low light, low contract things- which I was not doing. I was outside just taking a snapshot of someone (not portraiture)

2. I set the focus point in the middle, however, it keeps moving around when I press the *. How can I prevent this? (this is unrelated to the 1st question)

it is a 20d- I did have a telephoto lens on (however I think I was at the low end- 100mm), shutter speed was high enough so I dont think that would be an issue...I was at 1/80..i think...

Do you have a link to this photo?

Unfortunetly no- just took them on my lunch break. Basicly, I focused on the person and had a large ap (f/4 i belive) when I focused, everything looked great, however when I go back, the person was not in focus, it is not like her arm was in focus, but the face was not or anything. I tried to find what was in focus and was not really able to. It is not like she is completly OUT of focus, it is just not crisp at all. Also the color is not as vivid as it was when I looked through the lens- dont know if that has anything to do with anything...

Press the button directly to the right of the * button (I think its the AF selection buton or some such thing) while looking in your viewfinder, all the AF points will flash red. Then I forget what C. Fn. it is, but set the one for selecting AF points to the multi-controller. But hit the button to the right of the *, and then press the multi-controller straight in, the center AF point should flash, if it doesnt, hit the AF selection button again and try again. If you pushed the multi-controller up, you'll see the top AF point flash in the viewfinder, to the right, the right one will flash, etc. If you arent seeing the AF points flash, then your AF selection didnt happen, and the camera will continue to choose what AF points to use.

Thanks!! I thought I did that before- perhaps I did it wrong- Thanks again!

what was your shutter speed? if it was to slow it'll look out of focus.

it was at 1/80, I thought that would be enough, my other pics looked fine of buildings and such...

EDIT:: Holy cow I am an ass. I just zoomed up on all of my picks on the display and all of them are slightly off focus, I guess people are just more noticeable?? What range of speed should I have on there with this lens (70-200 f4-5.6) I took a picture of a gold plated fire hydrant at 1/400 and is was perfect...wait..as I am typing I am vaguely remembering something about if you have a 100 mm, the slowest you should go is 1/100 (200mm should be 1/200 right?)

Live and learn....this is why I am getting out at lunch so I can make my mistakes and learn form them (and at the same time waste everyone's time here on the forum)

Yeah, your "focus problem" is called camera shake. The camera just wasnt steady enough to get a clear shot at that shutter speed. Live and learn.

am I at least thinking clearly on the rule of slowest shutter speed? It goes something like that- right? 200mm do not shoot slower than 1/200 or 150 dont shoot lower that 1/150....

As a general rule, yes.

The general rule for shutter speed is 1/(focal length) and that is if you're holding the camera correctly. If possible try to brace your body to a solid object to minimize the shakes.

Breath control helps too.

It sounds like you are trying to check focus on your camera LCD screen which is a no-no because there aren't enough pixels in it for that. You'll have to download them to a computer and see how they look then.

Since you're using the 20D, you should use 1/(f.l.*1.6), as the 1/f.l. was formulated for full-frame 35 mm cameras, and when you enlarge your 20D's pictures to the same print size, the extra enlargement also enlarges the shakes more. So at 200 mm, try keeping to 1/350 or so. At 70 mm, make it 1/125 ofr better.