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Old May 27, 2003, 2:56 PM   #1
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Default When to use the 7 point AF system?

Hello all,

Playing with my 10D now for a while, I noticed that the 7 point AF system is really good at focussing on a point I do not want it to focus on. This is especially bothersome in close up portraits shots, with a wide aperture. For example, a mother holding a baby and the AF system focussing on the face of the mother instead of the face of the baby. The result is a blurry baby, and a hair-sharp mommy nose

Thus I switched over to the single (center) point AF system, which makes it possible for me to focus where I want it to focus.

Ok, now my question. What situations do people use the full 7 point AF system? I can see it being useful in the A-dep setting (in fact, that setting does always use the 7-point system).

Or a different question, what am I doing wrong?

Thanks!
Barthold
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Old May 27, 2003, 8:54 PM   #2
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when you are shooting is it available light or stobe? you have to take into account depth of field. especially if your shooting wide open.

using various points in the image for focus allows for non centralized (center spot) focus. this can in certain situations can enhance your image and creativity. on the other hand it takes some learning to use in conjunction with knowing DOF.

practice, practice, practice.
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Old May 27, 2003, 9:50 PM   #3
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Hi Sjms,

My example was with available (outdoor) light. Now all I need to do is find those certain situations where 7 point AF is the right thing to use As you said, lots of practice. Which is easy, and fun, with a digital camera!

Thanks,
Barthold
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Old May 27, 2003, 11:44 PM   #4
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It is my understanding (from reading the manual and posts) that using the full 7-point AF system is exactly not what you want when doing portraits. It seems most useful (to me) when the target is moving and it can track it using the AI-servo mode.

Itís amazing what sticks in your memory, and I haven't even eaten fish recently! I read this post from back in April at dpreview.com and all you're questions will be answered (at least read the first post... the whole thread is good, but long):

http://forums.dpreview.com/forums/re...essage=4887139

or this more recent one (read the whole thread, itís short):
http://forums.dpreview.com/forums/re...essage=4955120

If you have all points active I believe it picks the AF point it thinks has the closest target. Rarely is that what you want. Also, AF-Servo seems to decide when to switch to Servo mode... and does it badly. You should be using the center point and recompose. I'd lock the AF & exposure with either separate buttons through the custom functions or you can set the shutter button to do it.
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Old May 28, 2003, 1:14 AM   #5
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Thanks Eric, those links were useful! Especially the first one with the pictures showing how AF Servo works.

Still don't know exactly when to use the 7 points in One Shot mode, but I'll experiment.

Barthold
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Old May 28, 2003, 9:31 AM   #6
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The full 7 points focus is applied for the full auto mode, when you absolutely depend on the camera and let the camera does the focus for you. This in one of Canon's selling point when they said: look to the viewfinder and the camera will focus on the subject for you. Well, the camera is programed to deal with most average scene, and you will not always have the average scene, it doesn't see or think like a human brain and sometimes will be fool with the low and high contrast scences, but if you look at the view finder, and use this mode, sometimes you will find out for yourself, it doesn't focus on the subject that you want to focus.

If you look at the Elan7E and the EOS3 (has 45 points of focus points), and they work the same way, the only thing different is these camera have the eye control focus features, and they do work better since wherever your eyes look at, they will focus at what you look at( eye control focus sometimes doesn't work well for heavy eye glasses users). At an experience photgrapher, you will never rely on this mode, you have the 7 points of focus points, just use the thumbwheel on the back of the camera and select which one you want to use and lock on the focus. My preference one is the center, because it can focus on the subject both vertical and horizontal, and focus faster than any other focus points. Stay way from the full auto mode, you probably won't miss anything at all. This mode is designed for the P/S camera's users, but then why do they have problem? well, remember, they use to have the P/S camera with just one AF point, now with 7 points, they need to learn how to master this function of the camera and to undertand the its principal and limitation.
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Old May 28, 2003, 9:31 AM   #7
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Personally, 7-point in One Shot mode scares me. Letting the camera pick the AF point just seems like it's asking for trouble. Maybe I'm missing something? (I don't have my 10D yet to try it out.) I'd rather tell the camera "Do it this way" than hope it's thinking the way I am and will pick the same AF point I think is right.

It's posts like the ones I linked to which are the reason I read dpreview. There is a lot of annoying stuff which is a waste of time, but some times there are real gems there.
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Old Jun 6, 2003, 10:23 AM   #8
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This is a related, but different question that I posted once before with only one reply.

It is well known that good composition often results from rule of thirds. (Placing subject point of interest at intersection of horiz and vert lines dividing frame into thirds.)

So wouldn't it be logical for camera to position 4 of the selectable focus points at those points and one at center?
That would surely eliminate the need to lock focus and recompose many simple shots.

Do any cameras have their focus points placed that way?
If not, what am I missing? :?:
BTW I am new to Forums. Should I have started a new topic for a related but different question such as this?
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Old Jun 6, 2003, 1:37 PM   #9
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Actually in A-Dep you can point one sensor @ the shortest (for example the left one), and the other one @ the longest (for example the right one), and everything in between should be in focus!(page 88 of manual) 8) 8) 8)

You can also program the thumb button in C.Fn-17 #3 so it alternates between tracking and manual (C.Fn-13 will pick which one) when the thumb button is pushed! :P

BTW C.Fn-04 #1 is the other alternate as well...
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