Back focus

[reynolw]

I have a 10D and currently experiencing inconsistant focusing while photographing an outdoor sports event. Someone has suggested I use "back focusing".

Question - What is back focusing? What are the benefits? How do I get it to work on my 10D?

Many thanks in advance.

[jbradc]

back focus is a bad thing, it means your camera focuses behind the subject you are trying to focus on. Read this it will help you understand the issue.
http://www.photo.net/learn/focustest/

[DaveG]

I have a 10D and currently experiencing inconsistant focusing while photographing an outdoor sports event. Someone has suggested I use "back focusing".

Question - What is back focusing? What are the benefits? How do I get it to work on my 10D?

Many thanks in advance.

I think that person meant "Back Button" focus.

If you go into Custom function 4 you'll see that it defaults to 0 and you focus the camera by pressing the shutter button down a little bit. This you already know.

If you change the CF4 from 0 to either 1 or 3 you enable the * (asterick) button on the back of the camera. The * is near the natural location of your right thumb, and you press the * with your thumb (duh) to start the auto focus. I changed my 10D to this 18 months ago (and the 20D the moment I got it) and think that its a great improvement over shutter button AF.

This DOES disable the shutterbutton AF, so be aware of that - although you can always change it back if you don't like it.

If you look at this: http://www.dpreview.com/reviews/canoneos10d/page10.asp it'll show you all the different things that can be done with the custom functions,including CF4 and its various capabilities.

[wolf]

Do you have the center AF point selected on the focusing screen and focusing mode set to AI Servo or AI Focus?

[DaveG]

Do you have the center AF point selected on the focusing screen and focusing mode set to AI Servo or AI Focus?

It doesn't matter. The back button focuses just like the shutter button focus would. I use mine on One Shot, AF Servo or AF Focus. It's all the same. Enabling any or all of the focusing rectagles makes no difference either. All of this works with back focus.

This is off-point but I'll mention it anyway: When the 10D or the 20D are on One Shot (that's AF One Shot, NOT motordrive One Shot) and all of the autofocusing rectagles are enabled, the camera will use the flash (internal or any E-TTL flash) to help it focus even in total darkness. If you use just the centre rectagles it should work OK, too. But if only one of the outside AF rectagles is enabled then it won't work, and if you're like me it'll take some time to figure out why.

[wolf]

reynolw, if you have all AF points active the camera could be focusing on something in the foreground or background and not on the object you wanted. This is why I asked you if you have just the center AF point activated.

Also if you have your camera set to AF One Shot and you focus on something then point the camera to a new object while holding down the shutter button halfway the new object would most likely be out of focus.

If you set your camera to AI Servo or AI Focus the camera will refocus as you follow the action or move from one object to another.