# Exposure compensation/f-stop question



## manicmike (Mar 23, 2010)

I'm not sure how basic this question is but what is the difference between setting your exposure compensation two stops underexposed and stopping down your f-stop by two stops?


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## Garball (Mar 23, 2010)

Just watch you settings as you compensate the two stops and you'll see you reach the same result. (assuming your on aperture priority)

You shutter speed would have to remain constant in this example.
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## NateWagner (Mar 23, 2010)

It depends on what mode you are in. 

The main thing to realize is that exposure compensation is inherently a camera controlled aspect. It is the camera adjusting the shutter speed or the ISO to either under or over expose an image. 

So, if you are in shutter priority mode for example, and you use exposure compensation to knock it down to stops the camera will adjust the aperture down two stops. 

If you are in aperture priority and bump the Exposure compensation down two stops it will bump the shutter speed down two stops. 

Either way the exposure would be about the same (though obviously differences in either blur or DOF one way or the other).


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## Garbz (Mar 24, 2010)

The more obvious difference is that adjusting any settings does not do any compensation to the camera's exposure meter. 

In Aperture priority if you stop down the aperture, then the shutter would decrease to bring the image back up.
In Shutter priority if you speed up the shutter, the aperture would open up to bring the image back up.
In Manual if you stop down the aperture the camera's exposure meter would tell you that you're under exposing.

Dialling in exposure compensation biases this selection to change the ultimate brightness of the exposure meter in the camera. It will then purposely pick an aperture or shutter speed that darkens or brightens the image, and in manual mode it will tell you you're correctly exposing when you dial in the correctly adjusted settings.


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## Hamtastic (Mar 24, 2010)

Adjusting exposure compensation -2 tells the meter to expose 2 stops under middle gray (1/4th the light).  Which of the 3 exposure controls (aperture, shutter, ISO) it uses depends on the exposure mode it's in.

The effects of closing the aperture 2 stops also depends on the mode the camera is in.  In M it would expose 2 stops under middle gray.  In Av it would still expose for middle gray.


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## PhotoXopher (Mar 24, 2010)

manicmike said:


> I'm not sure how basic this question is but what is the difference between setting your exposure compensation two stops underexposed and stopping down your f-stop by two stops?



I typically use exposure compensation in aperture priority mode, it usually gives me the flexibility I need to make a creative exposure vs 'correct' exposure. In this example it would underexpose the photo 2 stops.

However if you're just adjusting the f-stop down and setting for 'proper' exposure it won't change the actual exposure at all, it will just increase or decrease the shutter speed accordingly.


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## manicmike (Mar 24, 2010)

Thanks for the info everyone.


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