focus question

I don't have any issues with focus when i do my studio work, but when i do larger groups, i have a nack for taking slightly out of focus pics. i think this is because i dont always have a focus point on someone's face. so i focus on the face and recompose -which i realize may be my whole problem since the distance from the lense to their face is different than that from the lense to their hands per say, if thats where the focus points line up.

if you are taking a picture of a group of subjects, obviously you need a higher F-Stop for DOF, but if none of their faces fall on a focus point, do you just focus on anything in the frontal plane?

I use f/8 and focus 1/3 of the way into the group. Your average lens is sharpest at f/8 and has 1/3 focus in front of your focal point and 2/3 back focus...That being said, you should do tests with all the aperature settings on all your lenses. But, Canon shoots to have the sharpest image come out at f/8...that's the industry standard.

if its a group then your going to be further back ( more dof ) also i would think your using a standerd or wide angle so unless your wide open i would think f5.6 or smaller would well cover the focus reconpose errors .
Could the probelm be something else ?
Rob.

how do you focus on someone in the second row, if you don't have an AF point on any of them. you cant aim up and focus, then recompose because the camera angle is changing and the distance between the original focus point and the new focus point are different. does this make sense?

also, i almost always shoot F8 or F11 at about 10-15 feet, Usually between 30 and 80mm. this should provide plenty of DOF. it's not a camera problem, as much it is a user problem.

It's pretty simple - manual focus or set the autofocus to use only the center focus point.

The idea is to control your camera - don't let your camera control you.

Lenses are a different story though, right?

even if i change to the center af, what if that af point, when the picture is composed, is lined up with someones hand in the first row. then i am focusing on their hand. i guess i am saying that when you focus on a face and then aim back down, your no longer in focus. isnt that correct?

If you are using autofocus and standard settings for all Custom Functions, you - with the center-point-only selected - would aim the center of the camera at the point that you want to focus on and half-press the shutter button. Then you would re-frame and take the shot.

I much prefer to have Custom Function 4 set to the "1" selection so that autofocus works ONLY when you press the * button (under your right thumb). That way, I focus on something by aiming the camera and tapping the * button, then I take the shot.

Sometimes I use auto exposure modes, but most often I am using manual (the M position) and have preset the shutter speed and aperture for what I want it to be.

With the standard 20D setup (and I presume the same for the 30D), both exposure control and focus would do its thing when you half-press the shutter button, and if you keep the button half-pressed you can re-frame the shot before pressing the button all the way to take the shot.

Manual focussing is another way to take control of the camera, of course.

ok, that is what i do. but if you have a person six ft tall. you are standing ten feet from him. you aim your center point up at his face. focus, and hold the focus while you recompse the shot, as soon as you like your focus point at him somewhere else, you are now no longer in focus. the distance from the lense to his face (your camera aimed up) is different from the lense to his waste which is where it would be when you recompose the shot. if that is correct, then the shot would be out of focus. which is what i think is happening to me.

Pick a focussing point that will be at your median distance.

The problem is, I think, that you're letting the camera figure out which point to use when using center-point-only will give you the choice. What you need to do is to find a contrasty target for the autofocus - and a face may not be the best - that is at the same distance from the camera as you want the primary focussing point to be, lock it, then reframe. It isn't really all that difficult.

Has anyone tried A-DEP mode, I believe it is for this kind of shot.

ok, you are all probably thinking.. this guy should not be holding a camera. but i am simplying trying to see if what i do is what you guys do. i have attached a simple image explaining my theory. if you focus on point y. and then recompose on point x. then you would not have the subject in focus. because their distances do not match if overlapped, correct? when i do this, my pics are slightly out of focus.

would this be correct, and would you be able to notice the difference like i think i can. or is it just me..lol

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No, you're quite right - focus-recompose can cause OOF problems for exactly the reason you deduced. How noticeable it is will depend on how far apart the two points are. For instance, if you focussed on someone at the extreme end of the group, then recomposed to center the group, you'd be way off. If you focussed on the front row and angled the camera up a tad to include the middle row, it'd be less pronounced.

with that being stated. how then, do you take a shot of a group of people if no af points end up where you want them to, without this happening. am i better off to just focus on the front of the subjects?

You could always ask one of the group to move to where you want the focus point to be, or move yourself back/forward to focus on someone the "right distance" away, then reposition yourself to the original shooting position. Me, I just stop down as much as I can, move back, and use a longer lens.