AI servo and metering

[niv2]

Apologies for the question, but I cannot seem to find an answer.

If I am using AI servo to focus on a Canon 50d with the shutter button half pressed following a subject, when does the camera calculate exposure......at the time the shutter button is half pressed or does it continuously update exposure until the button is fully pressed?

 

[fixedimage]

When you do the half press. I think.
Independent control of focus and exposure lock is one of the good reasons to move to back button focusing.

 

[TinaC]

When you do the half press. I think.
Independent control of focus and exposure lock is one of the good reasons to move to back button focusing.

I keep reading about this back button focus; what is it?

 

[tijuana taxi]

Basically takes away the focus operation from the shutter button and transfers it to a button on the back.

On a 400D it would transfer to the * button, been using it for a while now and very handy indeed, this is a much more in depth explanation

http://www.learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml

 

[fixedimage]

It's a custom function which means that half pressing the shutter button doesn't activate autofocus, this is now done by pressing a button on the back with your thumb. The one with the * by it on the 5D and 1D, probably the same on most Canons.
The half press on the shutter locks exposure when you set this up.

I find it means I never have to change AF mode or use exposure compensation now.

 

[posiview]

Basically takes away the focus operation from the shutter button and transfers it to a button on the back. You can either lock the meter reading when you focus or leave that on the shutter button

On a 400D it would transfer to the * button, been using it for a while now and very handy indeed

I use back button focusing and it just feels better when I lock the focus.

 

[TinaC]

Basically takes away the focus operation from the shutter button and transfers it to a button on the back.

On a 400D it would transfer to the * button, been using it for a while now and very handy indeed, this is a much more in depth explanation

http://www.learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml

Thanks for that Rich Another day I've learned something so I know I'm not dead yet

 

[seriousrikk]

You can set up custom functions to make the metering behave how you wish.

So a half press can do AE lock - or if you don't want it to exposure will be calculated when you fully press the shutter.

I can't remember which custom function it is - but you should be able to find it in the manual now you know what to look for.

 

[niv2]

Should have done this before I posted question....picked up my camera and set it to AI servo and then pointed it at various subjects with shutter button half pressed.....exposure continuously updates itself until the button is fully depressed to take shot....there answered my own question...

Thanks for input and apologies for being so stupid....

 

[big soft moose]

Basically takes away the focus operation from the shutter button and transfers it to a button on the back.

On a 400D it would transfer to the * button, been using it for a while now and very handy indeed, this is a much more in depth explanation

http://www.learn.usa.canon.com/resources/articles/2011/backbutton_af_article.shtml

Nice - another thing I didnt know (I wonder if the 20D has that ?)