AE lock and Metering questions.

[James.Thomas]

Hello everyone.

I have a Canon 550D,which I'm gradually learning the basics of the modes and options from books and reading topics on here.

But recently I have been reading a few threads on here about using the spot metering etc.to lock an exposure reading to find out the different readings over seperate parts of a scene using the exposure dial.

Which brings me to my 2 questions:

After trying this method today,I can't seem to get the exposure dial to move anywhere but the centre when locking the exposure if I use AV or TV modes,even on completely different contrasts such as grass and sky?
Is this method only possible on the full manual mode,or the semi auto modes also?

The other question I have is with the exposure lock.
I have read in my user manual that when the AE lock button is used it is shown in the viewfinder with a * sign,which only disappears when the button is pressed again,which confirms the cancelling of the curent exposure lock.
But as soon as I take a photo the * symbol disappears from the viewfinder automatically,so does this mean I have to lock the exposure before every shot?

Any help with the problems I'm having will be very much appreciated,and I apologise for the long winded post!

Many thanks in advance,

James.

 

[artyman]

First, if you are using Av or Tv the exposure guage is always sgoing to be in the centre unless you have dialled in compensation. If you point the metering area at different points you will see the shutter speed change in the viewfinder display, in Av. Or the aperture value change in Tv. That will give you an indication of the exposure needed for the specific part of the scene you are metering.

If you switch to manual and dial in your shutter speed and aperture, then move the camera round the scene you will see the indicator on the guauge move left and right indicating under or over exposure from the area you are metering.

Using the * button to lock a specific exposure in Av or Tv settings, will freeze the exposure at whatever was being metered at the time you pressed the * button. Say for example you wanted to get the sky right but weren't fussed about the foreground. You have to bear in mind though that the meter is trying to get an 18% grey, so for example metering of sunlit snow it is going to give you an underexposed reading, a deep blue twilight sky it would try to overexpose, so you have to interpret what the meter is seeing. Of course in Evaluative it would average out the whole scene to give whta it perceives to be an 18% grey.

I hope that makes things clearer.

 

[gnom]

1. In any mode but M the camera will always try and compensate to the best of its abilities to produce a correct exposure based on its reading. So if you're in Av it will set the shutter speed accordingly to produce a +-0 exposure. Same for Tv. You can use the big wheel on the back to increase or decrease the exposure if you wish.

2. If you want to lock the exposure for successive shots, keep pressing the AE lock button. This assumes you're using default setting in the camera (i.e. no back-button AF, for instance).

 

[James.Thomas]

First, if you are using Av or Tv the exposure guage is always sgoing to be in the centre unless you have dialled in compensation. If you point the metering area at different points you will see the shutter speed change in the viewfinder display, in Av. Or the aperture value change in Tv. That will give you an indication of the exposure needed for the specific part of the scene you are metering.

If you switch to manual and dial in your shutter speed and aperture, then move the camera round the scene you will see the indicator on the guauge move left and right indicating under or over exposure from the area you are metering.

Using the * button to lock a specific exposure in Av or Tv settings, will freeze the exposure at whatever was being metered at the time you pressed the * button. Say for example you wanted to get the sky right but weren't fussed about the foreground. You have to bear in mind though that the meter is trying to get an 18% grey, so for example metering of sunlit snow it is going to give you an underexposed reading, a deep blue twilight sky it would try to overexpose, so you have to interpret what the meter is seeing. Of course in Evaluative it would average out the whole scene to give whta it perceives to be an 18% grey.

I hope that makes things clearer.

Thankyou for the replies.

OK that's where I was going wrong then,as I was overlooking the aperture and shutter speed readings and concentrating on the exposure dial itself in the AV and TV modes.

So for instance if the scene was brighter than the locked exposure,it would show me a larger number/narrow aperture reading in AV and a higher shutter speed in TV or vice versa for darker scenes?

 

[James.Thomas]

1. In any mode but M the camera will always try and compensate to the best of its abilities to produce a correct exposure based on its reading. So if you're in Av it will set the shutter speed accordingly to produce a +-0 exposure. Same for Tv. You can use the big wheel on the back to increase or decrease the exposure if you wish.

2. If you want to lock the exposure for successive shots, keep pressing the AE lock button. This assumes you're using default setting in the camera (i.e. no back-button AF, for instance).

So when you say for excessive shots,do you mean I have to press it before each exposure?

Say for example I was using the spot metering for a bird or motorsport vehicle in the snow as someone elses post was the other day.
Would the initial exposure lock remain until such time that the light may change etc. or the * button is pressed again to deactivate it,or would it be needed before every single shot?

 

[gnom]

So when you say for excessive shots,do you mean I have to press it before each exposure?

Say for example I was using the spot metering for a bird or motorsport vehicle in the snow as someone elses post was the other day.
Would the initial exposure lock remain until such time that the light may change etc. or the * button is pressed again to deactivate it,or would it be needed before every single shot?

No, you keep pressing it - i.e. press and hold it for all the shots you want to take with that exposure.

Check out this link, as it might explain it better than me:

http://usa.canon.com/dlc/controller?act=GetArticleAct&articleID=2547

 

[James.Thomas]

No, you keep pressing it - i.e. press and hold it for all the shots you want to take with that exposure.

Check out this link, as it might explain it better than me:

http://usa.canon.com/dlc/controller?act=GetArticleAct&articleID=2547

Many thanks for that link Gnom,it was very helpful

So if I was to be using spot metering on a subject with a dark or bright surrounding like the snow situation mentioned in my previous post. Would I still need to use compensation to obtain the correct exposure for the snow etc. even though I'm not actually metering for that area?

 

[BandyQuill]

Many thanks for that link Gnom,it was very helpful

So if I was to be using spot metering on a subject with a dark or bright surrounding like the snow situation mentioned in my previous post. Would I still need to use compensation to obtain the correct exposure for the snow etc. even though I'm not actually metering for that area?

yeah snow is an odd one, you need to make the image brighter, the camera will compensite for the bright white, and tends to make it either dark where there is a shadow or a funny colour (in my experience)