Auto focus question

Tachyon · 24 Jul 2012 at 21:11

Guys that have fairly recent cameras or maybe some of the older higher end cameras could maybe explain this to me regarding the multitude of AF points.

I currently use a 20D with it's 9 point AF system which would be considered fairly dated with regards to the the likes of the 7D and 5D3. (I'll use Canon examples as that's what I'm familiar with.)

Macro I manual focus, anything else I use centre point & recompose, I find it fairly straight forward. I don't mean this as any sort of criticism on so many points or that so many aren't necessary but what are the benefits of say a 61pt system on the 5D3. I honestly can't get my head round it, how do you select a point quickly or how does the right point select what you want and so on?

Really interested to hear how it works as I hear such systems are a huge improvement over the previous model which would maybe have a fairly similar setup to my own.

Raymond Lin · 24 Jul 2012 at 21:18

you use the wheels to move the points around, or use the stick.

You can move single or group.

The advantage comes when you shoot at wide apertures, with 1.2 focus and recompose means the focal plane has shifted and what you want in focus is no long in focus. Plus focus and recompose is slower.

You are still manually moving the focus points, you can actually have it show all 61, or 39 (or something, its just the crossed typed), or even less. The moving them around part is not slow but obviously you need to think ahead in your shot, plan where you want to place your subject before you pressing that shutter.

Guitarman0 · 24 Jul 2012 at 21:19

I personally own a 60D with 9 point AF as well but I could see more points being useful in 1) A studio environment when you use the camera on a tripod and dont want to have to constantly move it to focus (assuming you are auto focussing) or 2) During sports rather than have just one point to follow a subject having zones using many points to help track the subject.

Tachyon · 24 Jul 2012 at 21:28

Thanks for quick replies. I definitely get the wide aperture side as I have shot at 1.4 and lost shots recomposing. It's the 2nd part that I find interesting that it's slower to focus and recompose, I didn't realise you could flick through so many so quickly. I didn't realise you could move in groups as well.

The sports angle had me wondering too as I was trying think how could one point lock on to what I wanted to lock on to as there was so many and it would involve fast action as well but again you mention zones so I can see the benefit there. Thanks guys.

An Exception · 24 Jul 2012 at 21:32

Tachyon said:
Thanks for quick replies. I definitely get the wide aperture side as I have shot at 1.4 and lost shots recomposing. It's the 2nd part that I find interesting that it's slower to focus and recompose, I didn't realise you could flick through so many so quickly. I didn't realise you could move in groups as well.

You can't. I only have 11 focus points active 98% of the time.
The reason is that I can select any focus point on the rule of 1/3's in 2 button presses, and I can get to the centre focus point with 1 button press.

It is however faster is you need to take more than 1 frame. It also aids composition and accurate framing.

Devrij · 24 Jul 2012 at 21:33

I can imagine having a group of points on a car that you're panning would be handy, as if one point can't focus due to reflections etc the others will. Presumably there's some wizardry at work to decide what it thinks you want in focus. I was reading about how the 1dx can use colour to track a moving object (eg a small bird) and follow it with the focus points as it moves around the frame with continuous focus. And that sounds pretty epic.

Raymond Lin · 24 Jul 2012 at 21:42

Devrij said:
I can imagine having a group of points on a car that you're panning would be handy, as if one point can't focus due to reflections etc the others will. Presumably there's some wizardry at work to decide what it thinks you want in focus. I was reading about how the 1dx can use colour to track a moving object (eg a small bird) and follow it with the focus points as it moves around the frame with continuous focus. And that sounds pretty epic.

There are different modes you can select, i only had a flick through the manual and left it at default (general) but i remember there is one where it priorities an object coming towards the camera, one where it expects object coming into the frame (from outside the frame obviously), one for moving objects side to side, etc etc.

Tachyon · 24 Jul 2012 at 21:44

Something else that came into my head there and I don't know if any current models have it but I remember years ago and I'm thinking the 90's maybe Canon had an AF system that I think worked by what you looked at in the view finder. I know that's a bit OT from where I started off though with this thread.

I don't know if it was continued but I haven't heard of it in a camera for years now, maybe it was rubbish but it would probably have worked well with how An Exception has his AF points set up.

The 1dx using colour to track something would be fantastic for sports I'd imagine.

Raymond Lin · 24 Jul 2012 at 21:49

Its call eye control, the EOS 5 and EOS 30E had it. I have the 30E, can try it out now if i want with my current lenses

It requires calibrating, although works, even through glasses, it is not fool proof and often it misses as much as it hit. I found it more so on the side points, i.e. if i want it to focus on the right point i need to look more to the right side than the actual point to get it to "land" there.

Nexus · 24 Jul 2012 at 22:06

A read through the 5D mkiii manual also lists how all the different lenses effect the performance of the AF points. Some lenses will use everything in better combinations than other lenses will.