Lock Exposure/Metering


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hyde9

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Feb 17, 2009
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#1
Hi guys,

i am using a Canon 1000D. Have read the manual and tried experimenting. i still do not understand how partial and center weighted metering works. After taking photos of the same object using the same exposure settings, it seems to be the same. Can anyone explain them to me?

Also, i do not understand how to properly use lock exposure and under what circumstances.

Here is a theoretical situation:

Supposing i would want to take a photo of my model which is placed in front of a desk lamp, therefore the model which is in the foreground would appear dark while the background is very bright due to the lamp. However, the model is at the bottom of the picture, therefore i would need to use the bottom auto focus point. how do i manipulate the settings to make the model appear brighter without over exposure and making the light from the lamp look like a nuclear blast?
 

hyde9

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Feb 17, 2009
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#2
I have tried experimenting on the partial and center weighted metering when i was at a chalet. took pictures of my friends who stood with the sun behind them. so they appeared darker than the background. after playing around with the metering, it just made them look slightly brighter while the background seemed duller.
 

ortega

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Nov 2, 2004
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#3
if the background is bright and the foreground is in the shadows

just meter / base your exposure for the background

once you take a shot
look at your lcd screen, if it is still too bright for your liking then
dial in -EV for your exposure compensation.
 

Reportage

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Nov 24, 2008
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#4
to control the brightness in a matter of speaking, have to play with the shutter speed and iso speed as well as aperture size. Most of the time auto works fine but if in difficult cases, take Raw.
 

hyde9

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Feb 17, 2009
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#5
Hi guys, thanks for the replies. Yup i know that aperture size and shutter speed do affect the brightness, but was wondering in the chalet situation, is there a way to lighten the subjects while keeping the background bright?

Ortega, you mentioned that i would have to meter / base my exposure for the background, so do you mean that i should use center weighted metering to get my friends as the "metering" subjects while at the same time getting a slight under exposure for the picture overall?

Because from what I know so far, i tried to use partial metering while getting a slight under exposure, but the picture turned out a bit dim and not very vibrant....my understanding of the partial metering for Canon is that it sets the foreground subjects, which are against a bright background and averages the entire picture based on the darker subjects. so at the same time i intentionally under exposed the picture hoping that the background would not be too bright, but it turned out pretty dim as though it was taken just before the sun set! lol

sorry guys i'm a noob! have tried exposure compensation as you suggested but i don't really understand how it works...
 

ortega

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Nov 2, 2004
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#6
see here for a guide to centre weighted metering
http://www.all-things-photography.com/centre-weighted-metering.html

for centre weighted metering, it takes most of the metering from the centre, so it really depends on where you are pointing your meter
it would try to make that area in the centre 18% grey.
 

ortega

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Nov 2, 2004
23,694
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Singapore, Singapore, Singapor
#7
Here is a theoretical situation:

Supposing i would want to take a photo of my model which is placed in front of a desk lamp, therefore the model which is in the foreground would appear dark while the background is very bright due to the lamp. However, the model is at the bottom of the picture, therefore i would need to use the bottom auto focus point. how do i manipulate the settings to make the model appear brighter without over exposure and making the light from the lamp look like a nuclear blast?

place another desk lamp in front of the subject, so that the light from the original desk lamp and the light falling on your subject are roughly the same brightness
 

Jan 14, 2009
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TS84
#8
Hi guys,

i am using a Canon 1000D. Have read the manual and tried experimenting. i still do not understand how partial and center weighted metering works. After taking photos of the same object using the same exposure settings, it seems to be the same. Can anyone explain them to me?

Also, i do not understand how to properly use lock exposure and under what circumstances.

Here is a theoretical situation:

Supposing i would want to take a photo of my model which is placed in front of a desk lamp, therefore the model which is in the foreground would appear dark while the background is very bright due to the lamp. However, the model is at the bottom of the picture, therefore i would need to use the bottom auto focus point. how do i manipulate the settings to make the model appear brighter without over exposure and making the light from the lamp look like a nuclear blast?
1. Compose your subject and focus by half-way pressing the shutter button. Release the shutter button.
2. Meter to a "Gray" paper which you can usually can buy from any photo shop. (Alternatively, meter on a darker object in the room) - Press on the Lock Esposure button (the focus will stay after you locked-in your exposure).
3. Shot.

Since you have metered a darker part of the room, the camera light sensor thinks that the room is dark so it will compensate to make the image brighter.

Goodluck.
 

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ziploc

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Jan 17, 2002
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#9
Hi hyde9,

One of the most important thing to understand about center weighted and partial metering is that the camera will set the exposure to "mid tone" (18% grey) wrt the subject in the metering area. So for example, if you're using partial metering and meter off a white piece of paper, the paper will appear grey (mid tone) in the captured photo. In this case, if you have other objects in the same scene, they will look darker (as the photo is now underexposed). On the other hand, if you meter off a dark object, again the camera will set the exposure to make it grey, and if there are other objects they will look brighter then normal (the photo is overexposed). It is therefore important that you either meter off a mid tone object (e.g. 18% grey card, or other natural mid tone objects), or otherwise compensate for it, in order to get the correct exposure. Note that mid tone doesn't necesary mean grey, it could be any color (e.g. you can have bright red, mid red, dark red, etc, the important thing is the tonality instead of color).

Here is how to compensate:
Assuming a norminal dynamic range of 5 stops (5 EVs) as common in most digital cameras, an object close to 100% white would be +2.5EV, and an object close to 100% black would be -2.5 EV, with mid tone at 0 EV. So let's say you partial meter a very white object, and the meter says f/5.6 1/60s. In this case you could either dial in exposure compensation of +2.5 EV, or if you prefer, set to f/5.6 1/375s [edit: should be 1/11.5, from 1/60 -> 1/375 is -2.5 EV](or something close to this) in manual mode. It would be the same if you meter off a black object, except the compensation would be negative.

Also, remember to meter close to the object to get it entirely into the field of view of the sensor, and in the direction that you want to shoot to have the same lighting condition.

Hope that helps. :)
 

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hyde9

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Feb 17, 2009
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#10
Hi guys,

many thanks for your encouraging replies...will go home tonight to test what i have learned...hopefuuly won't let u guys down =)
 

hyde9

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Feb 17, 2009
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#11
Hi hyde9,

One of the most important thing to understand about center weighted and partial metering is that the camera will set the exposure to "mid tone" (18% grey) wrt the subject in the metering area. So for example, if you're using partial metering and meter off a white piece of paper, the paper will appear grey (mid tone) in the captured photo. In this case, if you have other objects in the same scene, they will look darker (as the photo is now underexposed). On the other hand, if you meter off a dark object, again the camera will set the exposure to make it grey, and if there are other objects they will look brighter then normal (the photo is overexposed). It is therefore important that you either meter off a mid tone object (e.g. 18% grey card, or other natural mid tone objects), or otherwise compensate for it, in order to get the correct exposure. Note that mid tone doesn't necesary mean grey, it could be any color (e.g. you can have bright red, mid red, dark red, etc, the important thing is the tonality instead of color).

Here is how to compensate:
Assuming a norminal dynamic range of 5 stops (5 EVs) as common in most digital cameras, an object close to 100% white would be +2.5EV, and an object close to 100% black would be -2.5 EV, with mid tone at 0 EV. So let's say you partial meter a very white object, and the meter says f/5.6 1/60s. In this case you could either dial in exposure compensation of +2.5 EV, or if you prefer, set to f/5.6 1/375s (or something close to this) in manual mode. It would be the same if you meter off a black object, except the compensation would be negative.

Also, remember to meter close to the object to get it entirely into the field of view of the sensor, and in the direction that you want to shoot to have the same lighting condition.

Hope that helps. :)

Hi ziploc, thanks for your detailed explanation. Sure learned more than fiddling my cam by myself haha. But I have 2 questions:

1) Let's say you use a faster shutter speed as opposed to exposure compensation, will the picture appear more natural tone wise? Because i know that shutter speed doesn't affect the tones, but i am not so sure about exposure compensation as I never really used it before.

2) When you guys say metering, am I right to say that means once i set the metering mode, i just aim at an object and press the exposure lock button?

Sorry for my noob questions..
 

ziploc

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Jan 17, 2002
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#12
Hi ziploc, thanks for your detailed explanation. Sure learned more than fiddling my cam by myself haha. But I have 2 questions:

1) Let's say you use a faster shutter speed as opposed to exposure compensation, will the picture appear more natural tone wise? Because i know that shutter speed doesn't affect the tones, but i am not so sure about exposure compensation as I never really used it before.

2) When you guys say metering, am I right to say that means once i set the metering mode, i just aim at an object and press the exposure lock button?

Sorry for my noob questions..
1) Using my example given above, the two ways did exactly the same thing. 1 EV = 1 stop. Since the aperture is fixed at f/5.6, let's look at the shutter speed, which starts at 1/60. 1/60 -> 1/125 is one stop. 1/125 -> 1/250 is another one stop. 1/250 -> 1/500 is also one stop. Since we need 2.5 stops, the shutter speed will be 1/(250+125) = 1/375. This is the same as dailing in +2.5 EV using exposure compensation dial. [edit: from 1/60 -> 1/375 is -2.5EV. For +2.5 EV it should be: 1/60 -> 1/30 -> 1/15 -> 1/11.5, sorry for the mistake]

2) If you're metering a reference object other then the subject you're shooting, you can use the AE lock to lock in the exposure given by the reference object before shifting to your subject. Example 1: to use an 18% grey card to set the exposure - partial meter the grey card, press and hold AE lock, recompose on your subject, focus, shoot. Example 2: to use a white paper to set exposure - dial in +2.5EV compensation, partial meter the paper, press and hold EV lock, recompose on your subject, focus, shoot.

Hope I answered your questions. :)
 

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hyde9

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Feb 17, 2009
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#13
Thanka alot ziploc! I sure learned alot. Now i just have to get home to test it out. haha here i am in office trying to picture how everything works in my head, and it sure isn't simple lol
 

ziploc

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Jan 17, 2002
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#14
1) Using my example given above, the two ways did exactly the same thing. 1 EV = 1 stop. Since the aperture is fixed at f/5.6, let's look at the shutter speed, which starts at 1/60. 1/60 -> 1/125 is one stop. 1/125 -> 1/250 is another one stop. 1/250 -> 1/500 is also one stop. Since we need 2.5 stops, the shutter speed will be 1/(250+125) = 1/375. This is the same as dailing in +2.5 EV using exposure compensation dial.
Erm... sorry I made a mistake here. Changing shutter speed from 1/60 to 1/375 is -2.5 EV instead of +2.5 EV since less light is entering the camera. For +2.5 EV it should be: 1/60 -> 1/30 -> 1/15 -> 1/11.5. Sorry for the confusion, paiseh. :p
 

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hyde9

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Feb 17, 2009
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#15
Haha no prob, i was reading so much I didn't even notice that a faster shutter speed would actually reduce the light. =)

actually is metering that important? i mean i would love to learn to use it, but it seems very confusing! and i can't duplicate the chalet incident haha so it all seems theoretical now! Because in daylight, sometimes the subject will appear darker than the background due to the strong sunlight. so was wondering what i could do before doing any post production (not that i actually know how to do post production haha)

so am trying to figure out what i could've done back then, the only thing i could think of is to use partial metering, and on my friends and knock up the exposure compenstaion up a few stops. which i still think is wrong though haha
 

ziploc

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Jan 17, 2002
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#16
Well, frankly speaking most of the time I shoot in matrix metering mode (evaluative mode in Canon). But it is good to know the basics of metering & exposure compensation, for tricky situations like backlighting etc. It is actually quite easy to recreate it at home, just put a lamp behind a teddy bear and there you have it. You can then experiment with different compensation values. It is a lot of fun really. :)
 

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