Thanskgiving is Coming!!

[lvstenys]

I have a question regarding the focus points of the 40D when shooting a family picture. do you guys use the center point shooting Av and focus it in the middle above the shoulders of the people? If you do that, only the middle will be sharp? Can i use all the points to stay light up in red then shoot the picture? Im trying to to figure how to set all the focus points to light up or two or three points across. I tried look at the manual but it doesn't help. I need some lessons on multiple focus points. I figured out how to do the single points.

[Tee Why]

I would use the center point AF point in Av mode and focus on the eyes of the person in the middle of the group and depending on how deep the group is, stop down on the aperture accordingly and then increase ISO to prevent camera shake. I'd say for an average group f8 to f16 will do fine.

[tzalman]

Like T Y said. When in auto point selection multiple points light up, the camera is actually using only one of those points and the others are lit because they fall within the DOF of the set aperture/focal length combo. I prefer to know exactly which point is the real one.
If you do that, only the middle will be sharp?
If you mean side to side, that depends on the quality of the lens and the f/stop, but at f/8 or f/11 any modern lens will be good from corner to corner. If you mean the depth of the sharpness forward and back away from the camera, the DOF ( http://www.dofmaster.com/dofjs.html ), that depends on the f/stop, the lens' focal length, your distance from the group and the size of the print you will be making. As T Y said, use f/8 to f/16.