Inconsistent Auto Focus - Do you use auto focus?

[IlluminatingPhoto]

I am having problems with my camera or lens having inconsistent focus problems. I will take 3 or 4 pictures and have the eyes as the focus point but only 1 of the pictures is sharp.

The setup that I am using right now is a Canon 7D fitted with a 28-135 mm lens. I don't have the pictures right now but I will add them once I get home.

I am using a single point in the center of the view finder as the focus point on the eye. Then holding the shutter button half way down and composing my picture. Typically I am using an f stop of about 6.3 and standing about 20 feet from my subject.

Could I be moving enough (couple inches) to make that big of a difference at 20' with an aperture of 6.3?

Does any one else have this problem. I understand that I am not using professional quality glass but I guess I would expect more consistency that 25% in sharp focus.

Do you use auto focus?
If so do you change the focus point in the camera so that you don't ahve to move after the focus is achieved?

I may be doing something wrong as well.

Let me know what you think.

Thanks

[OsmosisStudios]

With the examples you post, be sure to include the EXIF data (aperture, shutterspeed, iso, etc). Could not be a focus issue but something else.

[IlluminatingPhoto]

Ok here are the examples. I was wrong about the aperture. The pictures were at f 2.8 and with the 50mm lens but they were taken very quickly and I don't think that I took my finger off the shutter button to re focus.

Let me know what you think. Thanks

Here is the first with the eyes clear. A little tough to see at 750 pix.



Camera: Canon EOS 7D
Exposure: 0.004 sec (1/250)
Aperture: f/2.8
Focal Length: 50 mm
ISO Speed: 100
Exposure Bias: 0 EV
Flash: On, Fired

And the second picture with a slightly softer focus.



Camera: Canon EOS 7D
Exposure: 0.004 sec (1/250)
Aperture: f/2.8
Focal Length: 50 mm
ISO Speed: 100
Exposure Bias: 0 EV
Flash: On, Fired

[OsmosisStudios]

The second is slightly misfocused, probably from not taking your time to refocus. Theyve both also been subject to some pretty harsh jpg compression which is hurting more than anything else. Its actually making it hard to tell whether something is technically wrong or if it's just compression. The second is distinctly blurry.