Confused about focus points

[Chris215]

I've been using auto focus because it would select multiple focus points and I would re-focus until I have what I want in focus. But of course it's inaccurate most of the time so I want to switch to manual AF points, but how would I focus let's say a small group of people with one focus point? I also want to keep a decent DoF, so what would be a good range for aperture?

[TomMessenger:Photo]

As far as I understand, for a group of people you would want to use the multiple points an a smaller aperture to make sure everyone is in focus. The aperture would then depend on your distance from the group. Try some shots and see how the DOF comes out at different apertures.

Tom

[Chris215]

how do I select multiple AF points manually if it's possible? or do I use auto and just refocus until where I want it? That's where I'm confused at.

[TomMessenger:Photo]

Well I would just use the standard all points selected, but I'm no expert shooting people

[Chris215]

oh ok thanks, can someone explain to me the differences between shooting a single person vs 2-multiple people using manually, multiple, or auto AF points.

[JeffreyG]

how do I select multiple AF points manually if it's possible? or do I use auto and just refocus until where I want it? That's where I'm confused at.


Here is what you are missing conceptually. There can only ever be one plane that is at the absolute distance of focus at one time. Selecting multiple AF points does not magically make multiple things in focus. If you are in auto point selection and you see more than one point light up, it is simply a coincidence that those two points both lay on equally distant subjects.

To shoot a group, use a single AF point and focus on a person roughly in the middle of the group front to back. Then use a small enough aperture to ensure that the region of acceptably sharp focus on either side of the plane of focus is wide enough to cover the group.

Playing around with a DOF calculator online can give some idea of what apertures will work. For small groups f/8 or so is a good idea.

Counter to intuition, large groups can typically be shot with larger apertures because you will be further back and using a shorter focal length. Unless you really stack the group deep that is.

[Chris215]

thank you! now it makes much more sense.

[The Moose]

IIRC, the A-DEP mode on your camera lets you point at one subject that you want in focus and then you point at another and it selects the aperture it thinks will get both in focus as best it can. I never knew what it really did until I was reading my 1D manual the other day, it seemed to explain it better than my 400D manual. I've yet to try it out to see how well it really works.

[Chris215]

after playing with it, it works well but it set high apertures for most subject and will require a tripod for most situations with large groups.

[canonloader]

Nothing new there. If you have good light and can use ISO 400 or maybe ISO 200 and keep up shutter speeds over 1/125, then try using f/16 or so, which shoold give you good depth of field. But you should use a tripod and a remote cord. Maybe even mirror lockup to reduce any chance of motion blur. And shoot several frames to be sure.

after playing with it, it works well but it set high apertures for most subject and will require a tripod for most situations with large groups.

[PhotosGuy]

IIRC, the A-DEP mode on your camera lets you point at one subject that you want in focus and then you point at another and it selects the aperture it thinks will get both in focus as best it can. I suspect that you'll have to do that for every shot in a series? Not too user friendly if you're shooting a group & want several shots to insure that someone isn't blinking.
You could try transferring the setting the cam chose to manual, But I'd run a few tests first & see how close the A-DEP setting comes to the DOF charts.

[nwa2]

how do I select multiple AF points manually if it's possible? or do I use auto and just refocus until where I want it? That's where I'm confused at.

You can't.

You need to practice a bit of old fashioned technique and experiment with DoF and different apertures and focal lengths.

[Roona99]

Im suprised no one mentioned one very importand basic method.

Use single point AF and one shot focus:

1. lock the focus to the point you want to have 100% in focus
2. Compose the frame how you want to compose it (and keep the shutterbutton half way pressed all the time)
3. Press the shutter all the way.

There is a reason why the shutter button is 2 stage and not just single stage.
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