EV Compensation Explained

What is EV button and what it does...???

To put it simply, the EV button allows your to quickly underexpose (darken) or overexpose (brighten) your image. How it works is pretty simple. When you’re taking a photo, the camera’s job is to adjust itself by changing the shutter speed and/or apperture to properly expose your shot so that it’s not too bright or too dark. Some cameras do this better than others but that’s another story. When you play with the EV button, what you’re doing is telling the camera to either brighten or darken the photo from the optimal exposure it perceives. 

You can use the EV button in P (programed auto), S or Tv (shutter priority) or A (aperture priority) modes.

In P mode, the camera will adjust the EV by changing the shutter speed and/or the apperture. 

In S/Tv mode, since you set the shutter speed manually, it will adjust the aperture to compensate. 

In A mode, the camera will change the shutter speed since you manually control the apperture.

NB: You cannot use the EV button to under or overexpose your photo in M (manual) mode since you control both the shutter speed and aperture manually.

When to Use EV Compensation

- When you need more shutter speed
- When your subject is brighter/darker than your background
- Bright sky

So basically this EV button function is same as shutter speed and aperture in manual mode.

(source Digital Photography )