Exposure compensation confussion?

Freida

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Oct 22, 2010
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Hello guys,

I keep coming once in a while across this magical feature called Exposure compensation and I would like a little help why is it helpful or useful and more importantly how does it actually work.

I try to shoot manual so when the exposure looks wrong I will adjust aperture, shutter or ISO if needed but people keep mentioning that you can set things up once and then use the Exposure Compensation feature.

However, what does it actually do? Is it a post-processing feature that when you take a picture with RAW it will then apply 'filter' like thing and changes it? Or does it ignore the A,S & ISO setting and sets its own? Or something else?

My question is - is there any reduction in quality or anything?
Or if I have ISO 100, F2.8 and shutter 100 and I do +1EV it will then act as if it was ISO100, F3.5 and shutter 100? (or combination of these 3?)

Anyone can tell me how it works with usefulness? I try to focus on Portraiture so it may or may not be that useful to me but I would still like to learn :)
Thank you so much :)
 

anotherscotsman

macrumors 68010
Aug 2, 2014
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UK
Hello guys,

I keep coming once in a while across this magical feature called Exposure compensation and I would like a little help why is it helpful or useful and more importantly how does it actually work.

I try to shoot manual so when the exposure looks wrong I will adjust aperture, shutter or ISO if needed but people keep mentioning that you can set things up once and then use the Exposure Compensation feature.

However, what does it actually do? Is it a post-processing feature that when you take a picture with RAW it will then apply 'filter' like thing and changes it? Or does it ignore the A,S & ISO setting and sets its own? Or something else?

My question is - is there any reduction in quality or anything?
Or if I have ISO 100, F2.8 and shutter 100 and I do +1EV it will then act as if it was ISO100, F3.5 and shutter 100? (or combination of these 3?)

Anyone can tell me how it works with usefulness? I try to focus on Portraiture so it may or may not be that useful to me but I would still like to learn :)
Thank you so much :)
If you are setting exposure the way you want it for a particular scene then arguably you don't need to use exposure compensation. Exposure compensation is, in effect, a way of giving you a mechanism to override the camera's measurement of what it is programmed to take as the ideal exposure for a scene. For example, consider a scene filled with snow - the camera metering system wants to set this as a mid-grey sort of tone(not colour balance but exposure). You want it to be bright white so you can set exposure compensation to 'over-expose' by a stop or two to get what you want. If you just took the shot according to the camera's version of ideal exposure it would come out apparently dark. Probably most useful in one of the camera's automatic or semi-automatic shooting modes.

Hope I explained it in a useful way. Put the camera in a particular mode (eg aperture priority) and take a shot with no EC then take the same shot having dialled-in a couple of stops of over- or under-exposure (by whatever mechanism you camera provides eg dial) and see the effects for yourself. Like all tools, useful when you need it but you first have to recognise the need.
 

mollyc

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Aug 18, 2016
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If you are using manual mode then you don't need EC. You are doing in camera if you decide to meter +2/3 or -1, etc. You only use EC if you are shooting in a program mode and know that you want your exposure to be something other than -0-.
 

Freida

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Original poster
Oct 22, 2010
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Thank you guys. I've checked the wiki but I still haven't found how it actually works.

So my question is, does the camera take the picture with the settings thats selected and then apply post processing adjustment (something like I can do in Aperture)

OR

does the EC override the settings of the camera to a better one that fits the selected value? (ie, no postprocessing at all)
 

mollyc

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Aug 18, 2016
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No, there's no post processing done. It changes the actual settings. So if your base exposure was ISO 100, f/5.6, 1/250, then an EC of +1 would instead change your settings to ISO 200, f/5.6, 1/250 OR f/5.6, 1/125, etc. It would change the settings before the image was taken to give you an extra stop of light.

Just the same way that if you were in manual mode metering to -0-, if you wanted to instead meter to +1, you'd have to change your settings in camera before pressing the shutter button to do something that would add one stop of light.
 
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Freida

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Original poster
Oct 22, 2010
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No, there's no post processing done. It changes the actual settings. So if your base exposure was ISO 100, f/5.6, 1/250, then an EC of +1 would instead change your settings to ISO 200, f/5.6, 1/250 OR f/5.6, 1/125, etc. It would change the settings before the image was taken to give you an extra stop of light.

Just the same way that if you were in manual mode metering to -0-, if you wanted to instead meter to +1, you'd have to change your settings in camera before pressing the shutter button to do something that would add one stop of light.
Perfect, thank you. That was what I was wondering about. I might now give A mode a try too :)
 

kallisti

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Apr 22, 2003
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Some good replies above.

Basically, if you are letting the camera automatically adjust any settings that affect exposure (i.e. shutter speed, aperture, or ISO) then exposure compensation tells the camera to adjust what it thinks is the proper exposure by adjusting the variables that it has control over in a direction you feel is more appropriate.

So in program mode where the camera has control over all 3 variables, it takes its own exposure reading and then makes adjustments depending on how much exposure compensation you dial in. For example, if the camera exposure meter thinks that the scene requires the equivalent of f/8, 1/500th sec, ISO 400 and you dial in 1 stop of negative exposure compensation, then the camera will either stop down the aperture to f/11, change the shutter speed to 1/1000th, or lower the ISO to 200 (all changes that will result in a 1 stop decrease in exposure). In program mode, each camera has its own internal algorithm to determine which variable(s) it adjusts.

In less automated modes (i.e. aperture priority, shutter priority) then the aperture (or shutter speed) you have dialed in is fixed and the camera makes the exposure compensation adjustment to the remaining variables it still has control over (shutter speed or aperture) and ISO.

In manual mode the camera has no control over any of the variables and exposure compensation has no effect at all. With the caveat that some people shoot in manual mode but keep ISO set to auto. In that case, exposure compensation will affect the ISO the camera uses for the shot.

Since you state that you shoot portraits, there is one other potential caveat. If you are using speedlights or strobes set to TTL (through-the-lens). This is an automated mode for flashes that determines flash output based on the camera's internal metering of the scene. This gives the camera one more variable that it can adjust automatically. In this case, even if your camera is set to full manual mode (i.e. you are setting aperture, shutter speed, and ISO) exposure compensation can be used to adjust flash output. Again only an issue/option if your speedlights/strobes are using TTL metering for their output. If you are setting flash output manually, then exposure compensation doesn't apply.

As stated by others above, exposure compensation has no effect on the RAW (or JPEG) files in the processing sense. It is merely a convenient way for you to tell the camera that its automatic metering is "wrong" and to adjust any exposure settings it has control over (when shooting in a fully automated mode or a partially automated mode) in the direction you think is more appropriate.
 
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