Metering and focusing


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stylus

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Mar 9, 2008
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#1
Have a few questions on metering and focusing.

Say I wan to take a picture of a snowy tree against a blue sky, so I should use center weighted metering to meter off the blue sky then recompose the picture then shoot in order to get a nice exposure? If I am using auto-focus, since i pointed my focus point to the blue sky, wouldn't it focus there instead of the tree later when i recompose?

So is the only solution is to use manual focus or change AF point?
 

catchlights

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Sep 27, 2004
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#2
there is a bottom for locking the AF, call Auto Focusing Lock.

there is another bottom for you to lock the metering exposure, call AE lock.

check with your camera manual, each camera system might call it differently, where are there located on your camera and how to use them.
 

Feb 4, 2008
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#3
For me I'll just shoot, look at histogram, dial in +- exposure compensation, shoot again
 

stylus

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Mar 9, 2008
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#4
From what i read in the manual, the button is AE-L/AF-L allow u to maintain focus and exposure lock whilst leaving your hand off the shutter, so isn't it same as pressing half shutter?
 

Aspect

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Dec 2, 2004
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#5
From what i read in the manual, the button is AE-L/AF-L allow u to maintain focus and exposure lock whilst leaving your hand off the shutter, so isn't it same as pressing half shutter?
I think the button is configurable to either AE-L or AF-L.
If you set to AE-L:
Using your example, you would AE-L on the sky, then half-shutter to focus lock on the tree. The exposure will still be locked to the sky.
 

cater

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Apr 12, 2007
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#6
From what i read in the manual, the button is AE-L/AF-L allow u to maintain focus and exposure lock whilst leaving your hand off the shutter, so isn't it same as pressing half shutter?
When u do a 1/2 shuttle, u get both exposure and focus lock, so it doesnt allow u to re focus on ur subject.
 

skagen

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Oct 20, 2006
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#7
what camera do you have ? check your manual of how to use AE Lock.
 

stylus

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Mar 9, 2008
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#8
I see, thx for all the replies. Using a D40, i didn't know the button could be configured to either AE or AF lock, will check it out if i missed it in the manual.
 

mckenzy

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Feb 14, 2005
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#10
quite a few factors that haven't been brought up here...

what kind of shot is this? Landscape?
what about your depth of field?
are you metering to get correct exposure of the tree or, of the sky?
 

stylus

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Mar 9, 2008
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#11
Aspect: thx, the link was v helpful!

mckenzy: I saw this shot on a book and was wondering how to do it. I suppose its considered a landscape shot, although the picture was made up 70% by the snowy tree. hmmm...My main question here was about metering and focusing correctly in such bright situation, not DOF. Since my subject is the tree, i'm metering off the sky to get correct exposure for the white tree. If i meter the tree, i think whole picture would be underexpose. Am i right?
 

mckenzy

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Feb 14, 2005
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#13
"...metering off the sky to get correct exposure for the white tree..."

again, depends on the colour of the sky... ;p

Lets say that the picture you saw was the ACTUAL situation for light, then following a grey-scale (metered at 12% grey) will help you to expose for it correctly.

if you can identify any colour or object that is close to the 12% grey, meter for that and you should get the white snow as white snow and the sky as whatever the colour was in that scene.

http://www.photography.ca/phototips/meter.html
 

calebk

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Jul 25, 2006
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Clementi
#14
When u do a 1/2 shuttle, u get both exposure and focus lock, so it doesnt allow u to re focus on ur subject.
Firstly, there isn't such a thing as a shuttle on your camera.

Secondly, on most SLRs when you half-press your shutter release, you will only get AF lock, not AE lock, unless you configure it to do so on some cameras with custom settings. Usually you would meter for whatever you want to correctly expose, AE lock, then focus on your subject, then recompose for the shot.
 

Aspect

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Dec 2, 2004
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#15
Secondly, on most SLRs when you half-press your shutter release, you will only get AF lock, not AE lock, unless you configure it to do so on some cameras with custom settings.
I'm not sure about PRO SLRs, but I thought that most entry-level SLRs will, by default, lock both AF and AE when you half-press the shutter release.
 

stylus

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Mar 9, 2008
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#16
yes, according the link at kenrockwell, it locks both AE & AF when using the button on a D40. However it can be changed manually using custom setting.

"AE/AF lock (default) locks both for as long as you hold the button. You'll see "EL" in the bottom left of the finder when it's locked. There is no AF-L finder indication. "
 

calebk

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Jul 25, 2006
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Clementi
#18
I'm not sure about PRO SLRs, but I thought that most entry-level SLRs will, by default, lock both AF and AE when you half-press the shutter release.
It will perform AE and AF when you half press the shutter button, and AF will be locked at that focus distance (assuming you are not in C-AF).

AE lock will only be performed when you press the AE-L/AF-L button.
 

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