Focusing, the "the bane of my existence"

[mal from cessnock]

Focusing, the "the bane of my existence" – I’m hoping some of you can help me better understand my equipment.
I submitted an image for critique a year or so ago only to be told it was not focused and that subsequently the image “failed”. The contributors told me that using the focus recompose method wasn’t ideal if the subject were to move, just a frac after locking in the focus. It was suggested I use the “Al Focus”, the middle position AF selection which once the focus is locked, activates the servo if it detects the subject has moved. I like the suggestion but it has limitations which this thread relates to.
[http://www.ausphotography.net.au/forum/showthread.php?53531-Bubble-Boy&highlight=bubble] image no longer there?

I just shot a pseudo rock concert and was determined to at least get critical focus on an eye of the moving subject. But herein the trouble lies. I have a Canon 5DM2 which has 9 focusing points, Canon suggest you only use the centre dot since they consider it the most accurate.
So consider, when using the “Al Focus” facility it is a given that you line up a focus point (albeit the centre) with the eye of your subject.
Ok, I can relate to this but it dictates the composition making it impossible to capture the subject anywhere other than in the centre of the frame at least lined up with one of the eight other points (which Canon say aren’t very accurate). Getting the eye in this position probably means shooting from a greater distance than desire necessitating a massive crop in order to get the composition you are after.

If you’re still with me, am I getting it? Do you have experience with this and can you make any recommendations?
I have included an image from the shoot where I nailed good focus, but if I had a better understanding of the correct focusing technique I’d get many more nicely focused subjects.
The light was poor, even the spots so I needed to use 6400iso, between F/4 and F/2.8 with a shutter of about 160sec.

Thanks for any help you can give which will lead to better focusing.

[arthurking83]

I'm assuming that shutter is supposed to be 1/160s?

Anyhow, and again I have to assume.. this AI focus is servo mode, is where the camera continually focused until you make the exposure?(cross brand terminology!)

In Nikon parlance it's simply called Continuous mode(AF-S mode) where the camera is continually focusing until it's time to nail the shot.

For best results in using this method, it;s best to set the camera up so that you focus with the AF-On button(using your thumb) and having the shutter release separate from the focusing ability of the camera, and setting up your shot prior to framing, where the focus area is where you want it to be so that your ready to frame-focus-shoot in quick time.

I know that the 5D has this AF-On ability and the ability to separate the focusing from the exposure, as by default most cameras are set up to only expose once focus is confirmed.
In your menu, this will be called 'release priority'(or similar) where the camera can always make the exposure irrespective of whether focus is made or not. Then simply shoot three or so frames, and you should get a sharp shot in there somewhere, even with technically incorrect camera settings, like 1/30s for a moving subject, using a 135mm lens!

Canon is right in describing the central focus area as the most accurate, but the other focus squares are also pretty accurate too, just not as accurate(especially in dubious lighting situations).
The central AF square will contain cross hair type sensors(literally look like a plus sign +) that read contrast data in both horizontal and vertical directions. The periphery AF squares usually contain vertical sensors that read contrast data that is best set out in a horizontal manner.. that is a | type AF sensor will see = type contrast better than contrast that is vertically orientated... like this || .
As the eye is circular in shape, both sensor types should have no problem focusing .. the low light levels will cause issues, and so a faster lens is the best option.
As long as you can get a close approximation of an accurate focus point, shooting multiple frames helps to ensure that if the target is moving, or conversely you are(swaying to and fro) they hopefully may move into the zone of sharpness.

ISO 6400 and 1/160s, whilst not great, is not dastardly. Maybe it's just a matter of practise in both technique, and pre-empting when the best moment to shoot a burst is about to happen.

[Analog6]

You can't so single centre spot with e 5DMkII? That would solve the oproblem, but I've never used one. The manual (found online here) says it does on poage 95

[mal from cessnock]

You can't so single centre spot with e 5DMkII? That would solve the oproblem, but I've never used one. The manual (found online here) says it does on poage 95

I'm sorry Odille, but I don't understand what you mean will solve the problem - can you say again please?

[mal from cessnock]

Hey Odille, I've re read your post and I think I understand your comment...
Yes, of course you can spot meter with the 5DM2 but that's the problem - what if my subject's desired place in the frame doens't line up with one of the nine focus points? It means you have to put them behind a focus point at the expense of the composition.
Thankis for your input.

[Analog6]

Hey Odille, I've re read your post and I think I understand your comment...
Yes, of course you can spot meter with the 5DM2 but that's the problem - what if my subject's desired place in the frame doens't line up with one of the nine focus points? It means you have to put them behind a focus point at the expense of the composition.
Thankis for your input.

With what I highlighted the point of focus is ALWAYS the centre spot - ideal for figures on a stage. I used to use this with my Canon for surfing etc. I would only use the wider focussing options for landscapes.