Multi-point autofocus... beats me!

[macleoda]

Hope someone out there can straighten me out...

I am on my third EOS (currently 5D mark II) and think it's an outstanding machine. However I constantly use the centre focus point exclusively and never get good results by any other means. Can anyone out there help me with the following:

1. There must be a reason for Canon providing 9, or 47, or however many autofocus points. I know one explanation is to allow a shot to be composed without pre-focusing and re-framing... this might be true for some classes of photographer but for most of us it's far less hassle to reframe. So given I appear to be far from alone, why do they in fact bother? I think the point count on the new 1D mark IV is close to 50?

2. Just assuming for some reason I actually wanted to use all the focus points (e.g. in a fast moving situation with a small aperture, to increase my chances of getting a focus on something). How does the camera decide which of the points to use? Imagine I'm focusing on a child coming towards me against a background with a lot of well defined shapes or edges... two or three or more points might get a "lock" of some sort, how then does the camera decide?
- The best lock? (what lock is better than the rest?)
- The first lock?
- The closest-to-the-centre lock?
- etc
Most commentators seem to say things like "Oh it's eeny meeny miny mo on my camera" - but it isn't of course, this is a computer we're talking about, it HAS a logic even if we don't know what the logic is.

3. Why does no-one ever seem to ask my Q2? Surely ANYONE using multiple focus points (and there must be SOMEONE out there who is) needs to understand how the camera decides which to use, but it seems that no-one really knows the answer and yet no-one ever asks. If you understand the behaviour, as a user one could make an informed choice about using multiple points.

Thanks in advance if you can shed any light. It's really Q2 I am most intrigued by - I'd like to take better pictures and to improve my chances of getting the focus right in a non-static situation, I feel sure increasing my chances of a "hit" must help but without knowing how the camera decides it is, in fact, random at least to me.

Alastair

[collywobbles]

Re: Multi-point autofocus... beats me!

The camera will focus on whatever is closest with emphasis on the centre point. But I am like you and only have the centre point activated as I very rarely do "action" stuff.

[Woolley]

Re: Multi-point autofocus... beats me!

Mine stays on centre 99% of the time. Sometimes I'll select a different one (motorsport is useful to pick a top one so as to track on the driver's helmet). On the 7D, expanding that to the area should help if you're less than spot on with aiming at something travelling that fast, although I haven't tried it). Just occasionally I'll put the camera on a tripod and select the focus point for where the thing I want sharp is in the frame.

I think auto select is the camera's way of ensuring that the wrong thing is perfectly in focus...

[George Bear]

Re: Multi-point autofocus... beats me!

The original standard auto-focusing cameras focused in the centre of the scene. You had a marker in the centre of the viewfinder to indicate this single focus point. One of the advances in camera technology has been multipoint autofocus. This is where the camera has many different zones where the camera can focus. It is really useful because you can set the camera to automatically pick the focus point(s) or the photographer can manually select the point(s) using a thumb wheel to the points they want to be in focus. The whole point for multipoint auto focus is you don't have to have the subject in the centre of the viewfinder. Further advances allow the photographer to select a wider zone (expansion points), select the sensitivity to change, use spot AF etc. All this can make autofocus systems (as on the 7D and 1D4) have many configuration options. Then you have AF Mode (e.g. AI Servo AF) as well.

Mind you ... all that too complex ... set the lens to MF

[colin C]

Re: Multi-point autofocus... beats me!

The big buzzword of modern society is "Choice". Whether we want it, need it, have the skills to use it, or the experience to make it, seem secondary .................... it’s all for our own good!

Back to photography and before auto focus was manual. We focussed the lens using a matte screen in the viewfinder and more laterally, central focussing aids. Then came Auto and everything changed. Things got cleverer for the point'n'shoot market with face recognition, single face to start with and then multiple faces. All of a sudden, users were getting sharp pictures all the time, instead of just some of the time. Many were now good photographers and wanted to improve even more, so the next step was a DSLR.

DSLR's now need to cater for different skill levels and user requirements, so the choice gets quite complicated. Recent converts have enough other new things to learn, so full auto with face recognition is very welcome to them. Some still want full manual capability and somewhere in between are the rest of us. We generally want centre point, because it's better, more sensitive and may be the only one able to work with some telephoto lenses, especially if you fit and extender.

Compositionally, we are aware that having the subject smack bang in the centre isn't always best, so we have the option of using the centre focus spot and then engage focus lock to re-compose the picture. Sometimes this is too slow, so we move the focus point from the centre to some other convenient point.

For moving targets, you need other solutions. The centre point is still more sensitive, but even more with a moving target, it looks better in the final shot if they appear to have some space in front for them to move into, so that means choosing an alternative focus spot. Some targets move too fast and you cannot keep a single spot always on the target as you are tracking it; then you can choose the assist points. You still choose the main focus point, but you can choose a number of assist points where the camera will keep tracking if the subject wanders off a little. It seems to be more accurate if you choose a lower number of assist points.

Even with all those clever options, there are still situations where the camera will not/cannot focus. The focussing system relies on contrast within the subject and even tones, or complete lack of light can defeat the system. The solution there could be:

• Manual focus.

• Guess the distance and focus using the distance window on the lens.

• Use a Canon Speedlight to “pre-flash” the distance and communicate that distance to the lens.

So there you go, it’s all about choice under different shooting scenarios. Understand what it can do, then pick what you need.

Colin

[EOS_Jim]

Re: Multi-point autofocus... beats me!

Iuse a grip on the 5DII. If I turn the camera in portrait orientation to shoot an image of a person I want the eyes to be the focus so I move to the appropriate closest focus point to the eye I want in forcus and compose. I try not to focus recompose.

I generally use the centre but there are many times I use another focus point.

[briansquibb]

Re: Multi-point autofocus... beats me!

I have got very quick at doing focus recompose from candid shooting that I only do it that way even when there is more time.

I hold the camera in portrait mode so that my right hand is under the camera - I notice that others do it the other way. My way makes it difficult move the focuscpoint with the joystick on the fly.

[colin C]

Re: Multi-point autofocus... beats me!

I rarely move from the centrepoint. For wildlife, the composition works fine for me because if I am focussing on the eyes/head, by default there is more room infront of the subject. So the composition generally just falls into place without me having to be too conscious about it.

I have separated metering and focussing from the shutter button. I use the shutter button to meter and take the shot on the second pressure and I use * rear button to focus. This is really good for wildlife motorsports etc., but in my early days of using this method, it wasn't so good for portraits, or studio work. In those circumstances I would alter the focus point to a more appropriate one. I also did this for general photography and landscapes and then I thought: This is a bit slow and cumbersome. As I am using "Back Button Focus", why not try focussing with the centre point where I want to, lift my finger off the BBF while I re-compose and then use the front shutter button the meter and take the shot?

It was a little awkward to start with, but now it's unbelievably quick and second nature. Also, I don't need to change settings for different areas of photography.

Colin

[George Bear]

Re: Multi-point autofocus... beats me!

This should be a useful background to BBF. For more recent cameras refer to the manual (or other stuff on the Canon DLC and CPN).

[colin C]

Re: Multi-point autofocus... beats me!

Thanks for posting the link George

I hadn't previously considered section 4: Easier over-riding of AF with full-time manual focus

Colin

[EOS_Jim]

Re: Multi-point autofocus... beats me!

Nice link. Even withthe AF-On button I still use the * as it's closer to my thumb :)

[Les McLean]

Re: Multi-point autofocus... beats me!

For landscape shooting, the starting point is always the center-point, but inevitably I start moving the focal point around, particularly when I want near to far sharpness, therefore shifting the focal point around until I am focused on a point roughly a third of the way in. Also, on a 1 series body you can link spot metering to the active focus point, which is dead handy sometimes.

Also for portraits, I tend to shift the focus point around, often to rest on the eyes, also to shift the main subject off-center.