help with understanding af points

[goroush]

What does everyone suggest on the AF points does everyone use all 8 points?I shoot with
a Mark 5 II. I am using for shooting family of 4 shots mainly. Looking for lots of suggestions.It
seems like when i have it set o all of the pints sometimes it doenst light all of the me up anyways and some of the picture if want in focus is out of focus, i use av mode.

[sandpiper]

Very, very few people on this site use all points (at one time). The problem with selecting all the points to be active is that you are leaving it up to the camera to decide what it is you want in focus. It doesn't know what your subject is, so will pick the focus point that it thinks is over your subject and use that. The problem is, it will generally pick the nearest thing in the scene with good contrast, that may not be your subject. The camera doesn't know you are photographing auntie Maud on the sofa and not the book on the coffee table in front of her, so may decide that, as the book is closer, it is more likely to be the subject and focus on that.

That explains why you are getting shots that aren't focused in areas where you want. As to why they don't all light up, well, the one(s) that light up should be the one it is using to focus on and it is telling you where it is focusing. If more than one lights up, then they are covering objects at roughly the same distance, so it is telling you that both points will be covered.

Most people on here will just use a single point to focus with, and place that point over the subject to focus. You can either select a focus point, and shoot with that over your subject, or (if in one-shot focus mode) focus on the subject with the chosen focus point and then, whilst holding the shutter button at the half way mark, recompose your shot and push the release the rest of the way.

That gives you control over what is in focus, rather than letting the camera choose. Av mode won't affect focus in any way, other than the aperture you select will change the depth of field, so a wide aperture will mean the focus only covers a shallower area, a small aperture (larger number) will give an increased depth as to what is in acceptable focus.

[goroush]

Originally Posted by sandpiper

Very, very few people on this site use all points (at one time). The problem with selecting all the points to be active is that you are leaving it up to the camera to decide what it is you want in focus. It doesn't know what your subject is, so will pick the focus point that it thinks is over your subject and use that. The problem is, it will generally pick the nearest thing in the scene with good contrast, that may not be your subject. The camera doesn't know you are photographing auntie Maud on the sofa and not the book on the coffee table in front of her, so may decide that, as the book is closer, it is more likely to be the subject and focus on that.

That explains why you are getting shots that aren't focused in areas where you want. As to why they don't all light up, well, the one(s) that light up should be the one it is using to focus on and it is telling you where it is focusing. If more than one lights up, then they are covering objects at roughly the same distance, so it is telling you that both points will be covered.

Most people on here will just use a single point to focus with, and place that point over the subject to focus. You can either select a focus point, and shoot with that over your subject, or (if in one-shot focus mode) focus on the subject with the chosen focus point and then, whilst holding the shutter button at the half way mark, recompose your shot and push the release the rest of the way.

That gives you control over what is in focus, rather than letting the camera choose. Av mode won't affect focus in any way, other than the aperture you select will change the depth of field, so a wide aperture will mean the focus only covers a shallower area, a small aperture (larger number) will give an increased depth as to what is in acceptable focus.

thanks i use to use just one focus point, but it did seem like part of picture that i wanted to be in focus
would be out of focus i will keep trying thank.

[sandpiper]

Originally Posted by goroush

thanks i use to use just one focus point, but it did seem like part of picture that i wanted to be in focus
would be out of focus i will keep trying thank.

When you say "part of the picture" would be out of focus, do you mean the part you focused on, or just some other part? If the subject you focused on is OK but another bit you want in focus isn't, you need to increase your depth of field by using a smaller aperture. Adding more focus points won't let the camera focus on other parts of the picture as well, it can only focus on one exact distance. Anything nearer or further away than that distance will become less sharp the more you move away from the plane of focus (the distance you focused on). If you are using a wide aperture (small number) then the falloff in sharpness will happen much closer to the focus plane than when you use a small aperture.

[goroush]

Originally Posted by sandpiper

When you say "part of the picture" would be out of focus, do you mean the part you focused on, or just some other part? If the subject you focused on is OK but another bit you want in focus isn't, you need to increase your depth of field by using a smaller aperture. Adding more focus points won't let the camera focus on other parts of the picture as well, it can only focus on one exact distance. Anything nearer or further away than that distance will become less sharp the more you move away from the plane of focus (the distance you focused on). If you are using a wide aperture (small number) then the falloff in sharpness will happen much closer to the focus plane than when you use a small aperture.

thanks that make sense.I will will work with that,

[tonylong]

From the duplicate thread:

People suggest not using all focus points, unless you are shooting a rapidly moving subject in AI Servo mode, and even then with the 5D it's best to keep it on Center Point and keep that on the subject.

For "normal" shooting, use a selected point, because when you have the Auto point selection the camera chooses what to focus on which may or may not be what your want to focus on.

In good light, you can select any of your points for AF. In lower light, the Center point is the only one that will be reliable.

[Nathan]

Originally Posted by goroush

What does everyone suggest on the AF points does everyone use all 8 points?I shoot with
a Mark 5 II. I am using for shooting family of 4 shots mainly. Looking for lots of suggestions.It
seems like when i have it set o all of the pints sometimes it doenst light all of the me up anyways and some of the picture if want in focus is out of focus, i use av mode.

If I understand you correctly, it sounds like you expect all the focus points to light up at once so that everything you want to be in focus is indeed in focus. That's not how it works. When you set it to all focus points, the camera is free to use any one of them to achieve focus and decides which one to use. When you see 4 or 5 of them light up, the camera has chosen a few high contrast areas taht happen to be on the same(ish) focal plane. There is no way to have all the focus points light up unless all of them are pointed at subjects on the same plane.

[JasonMK]

Originally Posted by tonylong

From the duplicate thread:...In good light, you can select any of your points for AF. In lower light, the Center point is the only one that will be reliable.

Thanks for that point, did not know that.

[goroush]

thanks so much for all the tips.I am going to work with turning some of them of and see how that
does.

[tonylong]

Originally Posted by goroush

thanks so much for all the tips.I am going to work with turning some of them of and see how that
does.

Take some time to read your manual.

With the 5D2, you can either select "All points" or just select a "Single point". For "general" photography we here typically advise the single "Manual AF point selection" (check the index of your manual).

If you select the Center point you get the most accurate and responsive AF, and it works reasonably well in lower light. In better light, you can select one of the outer points, minimizing your need to "focus and recompose" to get the desired framing.

However, AI Servo AF has some different challenges as well as capabilities. If you select "Automatic AF point selection" (again, check your manual index) then the 5D has "invisible assist AF points" surrounding the center AF point that get turned on. With the 5D AI Servo AF with the "Automatic" functioning starts with the center point, then if the subject moves off-center it can use one of the invisible points to pick it up. Then, if the subject moves farther, ideally (good lighting conditions) one of the outer points can pick it up. Again, read your manual -- this stuff is covered in the "AI Servo AF" section.

I, however, in practice never turn on the "Automatic point selection" feature -- I stick to using the center point AF with AI Servo.