when does 400D do its exposure metering ?

[song]

Assume that i set my active focus point to be the center square.

When i press half-shutter to lock focus on my subject face, then i move the camera to frame in my desired composition. After that i continue my half shutter to a full shutter so as to complete my shooting.

The question is when did my 400D do its exposure metering? is it during the time when i press my half shutter to get a focus lock? If so, then when i recompose again with my half shutter still on, i would get in accurate exposure. How to overcome?

Please advise leh..thanks

[calebk]

Originally Posted by song Assume that i set my active focus point to be the center square. When i press half-shutter to lock focus on my subject face, then i move the camera to frame in my desired composition. After that i continue my half shutter to a full shutter so as to complete my shooting. The question is when did my 400D do its exposure metering? is it during the time when i press my half shutter to get a focus lock? If so, then when i recompose again with my half shutter still on, i would get in accurate exposure. How to overcome? Please advise leh..thanks

Exposure metering is ongoing. Meter a scene that has drastic changes in lighting and you'll realise your exposure meter jumps around continuously.

Referring to the bolded part, I think you mis-phrased your query, because I don't understand what you're trying to ask.

[song]

Originally Posted by calebk Exposure metering is ongoing. Meter a scene that has drastic changes in lighting and you'll realise your exposure meter jumps around continuously. Referring to the bolded part, I think you mis-phrased your query, because I don't understand what you're trying to ask.

Do you mean that after i half-press my shutter to lock focus, the metering is still on-going and changing . So when i recompose my picture, i do not have to worry about my exposure cos the exposure is not locked and still detecting right up to the last moment when i fully press my shutter. Is that what u mean?

I encounter this problem when i shoot a person standing on left and then there is a very strong light source on the right. When i focus lock on the left side using half shutter, the bright light on the right is not is the frame during the focus lock. Then after i focus lock, i recompose to include the right bright light source for the correct framing. I use evaluatative metering to get an average value for metering

[calebk]

Yes the metering does not lock, unless you press the AE-lock button (* logo).

Regarding the example you gave, because the intense light was not in the frame earlier on, the camera would meter for the person in the frame, but after you recompose, the camera would be fooled by the light and give a much darker exposure in order to expose for the light, hence your subject would be underexposed.

In such a scenario, I would shoot M mode so I control the exposure and not let the camera decide, because it can be fooled easily. If you do want to let the camera decide, then use partial metering and meter the person's face, after which you AE-lock that exposure value in and recompose, so that the camera will not readjust the exposure settings to expose for the bright light.

[denniskee]

if you do a simple google search, 'how does canon eos meter' you will find this

http://photonotes.org/articles/eos-flash/

it is like the bible of canon eos metering system.

[blurry80]

The above replies are only true if you did not meddle with the custom function.

[song]

Originally Posted by blurry80 The above replies are only true if you did not meddle with the custom function.

u mean custom function on the AE lock / AF lock switch changing??

[RCheah]

Originally Posted by calebk Exposure metering is ongoing. Meter a scene that has drastic changes in lighting and you'll realise your exposure meter jumps around continuously.

Actually when using Evaluative metering, and CFn-4 is default setting, half-press locks both AF and AE.

[RCheah]

Originally Posted by denniskee if you do a simple google search, 'how does canon eos meter' you will find this http://photonotes.org/articles/eos-flash/ it is like the bible of canon eos metering system.

Actually this is only for Canon Flash metering system, not the camera's ambient metering.

To the TS, in the scenario you mentioned, when you half-press and lock AF/AE, even though the bright light source is not in the frame, it may still mess up the camera's AE. Not sure why, the light could have strayed in somehow.

It's very hard to take strongly backlit photos. Do avoid if possible, or at least angle the subject sideways to the light source. If not possible to re-position, there are a few things you could do:

1. As what calebk suggested, to press the Partial Metering button * while the centre circle is on the subject's face. This takes exposure only in the circled area and locks the AE settings when you recompose the picture.
2. Use of exposure compensation.
3. Use manual settings, as what calebk has also suggested.
4. Use flash as fill-in to brighten the subject's face, and still avoid over-exposing the background.
5. If mounted on a tripod, take 2 shots of the same composition, one exposed correctly for the subject, the 2nd shot for the background. Then use post-processing to merge the correctly exposed subject onto the 2nd pic. Very tedious but probably give u the best pic.

[blurry80]

Originally Posted by song u mean custom function on the AE lock / AF lock switch changing??

yup, you can change the AE to lock together with the AF when it locks. i think the instructions are somewhere in the user manual.

Sometimes i use it when the light source is consistent.