Why are more/better AF points needed?

From what I gather reading the forums here, many people use the "center AF point back button focus" technique most of the time. If this is the case what benefit do such people get from moving to a camera with more AF points or even more cross type points? Aren't all of those extra AF points unused in that case? I'm sure I am missing something fundamental here.

I am not sure if you are asking a serious question here.

DaveSt wrote in post #14644195
From what I gather reading the forums here, many people use the "center AF point back button focus" technique most of the time. If this is the case what benefit do such people get from moving to a camera with more AF points or even more cross type points? Aren't all of those extra AF points unused in that case? I'm sure I am missing something fundamental here.

A lot of us do as you say, but more because we have to rather than want to. I would love to have to recompose less, but my 5D doesnt have the broadest spread on the focus points.

gonzogolf wrote in post #14644240
A lot of us do as you say, but more because we have to rather than want to. I would love to have to recompose less, but my 5D doesnt have the broadest spread on the focus points.

I have a 5D too. I only use the center point and recompose because my outer points suck. If I had better outer points, and they were spread out more, I'd use them a lot more. This is pretty much the only major reason I want the 5DMkIII.

Most people use the center AF or another single AF to ensure the object they want is in focus. You can alternatively use all the AF points and let the camera decide for you what if finds most interesting in the scene to focus on.

vipergts831 wrote in post #14644213
I am not sure if you are asking a serious question here.

I am being serious, but probably dense at the same time. When I first started using a "serious" camera the one piece of advice that seemed to help the most was that I should control what the camera is focussing on not vice-versa. To that end it seemed to be general practice to use the center focus point to capture the exact detail in the scene that was most important. I assumed that was why so many here advocate the BBF method. That got me wondering why having more focus points seems to be such a selling point. Maybe the old method is no longer valid.

BBF is a seperate subject to centre point/recompose.

I'll use the outer points if I can - Or rather if I'm shooting at f/1.4 & don't want to risk recomposing.

DaveSt wrote in post #14644289
I am being serious, but probably dense at the same time. When I first started using a "serious" camera the one piece of advice that seemed to help the most was that I should control what the camera is focussing on not vice-versa. To that end it seemed to be general practice to use the center focus point to capture the exact detail in the scene that was most important. I assumed that was why so many here advocate the BBF method. That got me wondering why having more focus points seems to be such a selling point. Maybe the old method is no longer valid.

Its still pretty valid with your camera and mine. But imagine you had a 5DIII with 60 points each as accurate as the center point on your camera. You would still select the point you want to be active, but its much more likely you could select one at the point of interest without recomposing.

DaveSt wrote in post #14644289
I am being serious, but probably dense at the same time. When I first started using a "serious" camera the one piece of advice that seemed to help the most was that I should control what the camera is focussing on not vice-versa. To that end it seemed to be general practice to use the center focus point to capture the exact detail in the scene that was most important. I assumed that was why so many here advocate the BBF method. That got me wondering why having more focus points seems to be such a selling point. Maybe the old method is no longer valid.

A lot of that has to do with scene composition, everyone has their own way of doing it. Another flexible AF perk is for moving subjects. Back button focusing is more geared towards action shooting where the subject moves and stops during shooting bouts. Not to say it can't be used under static conditions but one-shot AF seem to suit that better.

DaveSt wrote in post #14644289
When I first started using a "serious" camera the one piece of advice that seemed to help the most was that I should control what the camera is focussing on not vice-versa. To that end it seemed to be general practice to use the center focus point to capture the exact detail in the scene that was most important.

Center focus, somewhat dependent on the lens/body combination, is frequently the most accurate focus point, hence the tendency for many people to use it and do the button 1/2 down, focus, recompose, shoot scenario. That works well for a non-moving subject but depending on subject matter, movement, etc. that may just not work well, taking a picture of a 4-year old running around for instance. Hence the reason the back button focus technique was put into some cameras.

DaveSt wrote in post #14644195
From what I gather reading the forums here, many people use the "center AF point back button focus" technique most of the time. If this is the case what benefit do such people get from moving to a camera with more AF points or even more cross type points? Aren't all of those extra AF points unused in that case? I'm sure I am missing something fundamental here.

Not everybody uses center point and those who do don't necessarily always use only the center point. I mainly use the center point because most of my subjects are stationary and I also mainly use back button focusing along with AI Servo AF, but sometimes I use other focusing modes. When doing action shots such as sports or wild animals or birds in flight I might let the AF system track the target as it moves from one point to another across the field of view while keeping the camera steady. When doing that method of AF, it is necessary to designate one of the points to initiate the AF (whether center or some other point) so that the camera knows what to track. One might ask what is the purpose of this last method that I mentioned -- it is useful if you would like to have a slower shutter speed so that speed of the subject is conveyed in the image, but we do not want any blur of the surroundings due to camera movement.

Love my 5D II, but hate the focus points! I recompose A LOT. I only use the outer points if I'm using a large aperture. Or sometimes I even have better focus going manual.

Don't get confused with BBF and the use of various focus points.
Both my cameras are set to BBF,the 5D is invariably centre point and recompose,I tend use this camera for static objects.
The 7D on the other hand can be anything from all the focus points active( BIF with the sky as a background) to the sensitive spot focus for macro with anything in between depending on the subject.

Center focus point is the most accurate for fast apertures. More cross type AF points would reduce this advantage for using center AF point only.

Outer focus points reduce the focus-recompose error. More AF points help to further reduce the need for any recompose, or when the camera is tripod mounted and any recompose change is a nuisance.

The problem created by more AF points is that even the joystick selection of AF point takes a measureable amount of time to accomplish, and the selection via joystick does not always go directly to the one point which you want to use, which exacerbates the delay in focusing and taking a shot...not a good thing for action photography. Adding more AF points simply means more 'wrong choices' during joystick selection!

Where there are few targets (BIF against a blue sky), auto selection of AF points is useful, and having more AF points can work well.

Thanks everyone for the input. I had not thought about the recomposing angle honestly but that makes perfect sense. I guess I am so used to focusing with the center point and then recomposing that it just started to become the only way to do it in my head. I still have yet to master moving the focus point with the joystick on my 30D. It must be darned near mind boggling trying to do it on a camera with 60 AF points!