exposure lock and back button focusing

[kimberley]

Can someone explain this process to me?

I thought I had a handle on this, but I think I have been doing this all wrong.

I usually shoot in AV mode and shoot canon 30D

[Gordon]

What are you wanting to do ? Move the focus control on to the * button ? What problem are you having ?

[kimberley]

Well, I thought I was doing this correctly.

i shot in AV mode and in CWM

For example : I will set the aperture to 2.8 and let the camera meter the scene I will use the * to lock the exposure and then focus
(pressing the shutter half way recompose if necessary) and shoot.

I was told this was the worng way to do it. I was told that, that in fact was the focus lock button...so I wanted to see how others used this function.

[Gordon]

What you described is correct, for the normal set-up of the camera. It doesn't sound like you are doing anything wrong. When you press the * key, you should see an exposure value (aperture/ shutter speed) appear on the camera and not change while you move it around.

However, there is an alternative way to set up the camera, using custom functions, where you can move the autofocus operation from the half shutter press, to the * key. The autoexposure meter then becomes a half press of the shutter.

The advantage of that is that focusing and taking the picture become completely independent, but you still have autofocus whenever you want it. So you can focus on something, move the camera and shoot, without worrying about half pressing the shutter, or the camera jumping to focus on something else if you shoot a couple of frames, etc. Takes a bit of getting used to though, but all my cameras are set up that way now.

Makes it harder to give the camera to someone and have them shoot though ;)

[CaptainTom]

Gordon
It's about time I went to this focusing system.
I'm glad you'll be around to help if needed........

[Roy]

I changed my camera to focus this way about 3 weeks ago. I'm liking it better all the time.

[kizersoze]

Since you talked about focus & meter/recompose I thought I would introduce this. Depending on your aperature the focus/recompose method can introduce focusing problems or slightly out of focus results. I won't go into great depth but here is an article describing the issue.

http://visual-vacations.com/Photogra...pose_sucks.htm

ed

[Gordon]

Yup - I'd avoid doing much recomposition for the reasons in that article, particularly at a wide aperture or close range. I typically move the AF point around so that it is over the thing I want to focus on (the joy of having 45 points to pick from), so never usually move the camera much (the the subjects may well move around). I only use the center AF point if I'm really stuck.

But I still use the independent auto-focus/ shutter, so that the camera focuses when I want it to, not just 'because' before it takes a shot.

[xseption]

Originally Posted by Gordon

What you described is correct, for the normal set-up of the camera. It doesn't sound like you are doing anything wrong. When you press the * key, you should see an exposure value (aperture/ shutter speed) appear on the camera and not change while you move it around.

However, there is an alternative way to set up the camera, using custom functions, where you can move the autofocus operation from the half shutter press, to the * key. The autoexposure meter then becomes a half press of the shutter.

The advantage of that is that focusing and taking the picture become completely independent, but you still have autofocus whenever you want it. So you can focus on something, move the camera and shoot, without worrying about half pressing the shutter, or the camera jumping to focus on something else if you shoot a couple of frames, etc. Takes a bit of getting used to though, but all my cameras are set up that way now.

Makes it harder to give the camera to someone and have them shoot though ;)

Are these all the instructions? I think I am missing a step or two there ... can you be more explicit? or is it in the manual? I have a Rebel XTi ...

Thanks!

~ edd

[kizersoze]

There should be instructions in the manual about setting the custom functions. I'm not sure if the XTi is the same as the 30D but it might be, and if so then it would be custom function 4. Here are some related links on the topic. I havn't tried this method myself but intend on trying it soon!

http://www.photography-on-the.net/fo...ustom+Function

http://www.photography-on-the.net/fo...ustom+Function

ed

[Gordon]

This is controlled by Custom Function 4 C.Fn-4 : Shutter/AE lock button

The default (mode 0) has shutter doing auto focus, AE lock button (*) doing AE lock

Mode 1 does what I described, shutter does AE Lock, * button does Auto focus

There are a couple of other modes, that I've never used, that change how the camera tracks in AI servo AF operation.