Auto ev compensation

Could someone explain me what exactly happens when I set the AUTO EV compensation on a k5? Also if changes according the current mode selected.

Its a kind of 'safety net' setting, to prevent gross exposure error caused by setting a combination of aperture / shutter speed / and ISO that results in such an extreme exposure.

Whichever variable is active according to the Mode will be changed to a value that gives the metered exposure. Its like temporarily dialing in so many stops of EV to 'correct' the exposure.

Does it work with all the modes? Including manual mode?

No, it has no effect in M, X or B modes.

In extreme overexposed situations the user-set value that can be adjusted will be flashing. With auto-ec activated you won't see this, but nor will you get any idea of where you're going wrong.

Do you think makes any sense to use this option?

Also there is something I am missing. If it works only in automatic modes, shouldn't the auto modes already use the best settings?

I'll try and give an example - lets say we're in Av mode in very bright conditions, and ISO is already set to 100. You want to take a shot with a very small depth of field, so you dial in the smallest aperture - lets say this was f1.8.

In very bright conditions this could easily produce a shutter speed at the meter determined EV value that was in excess of the maximum possible - say 1/8000 sec. Without auto ec activated, the shutter speed would flash indictating too bright for the settings. You would then have to stop down the aperture until the shutter speed stopped flashing and showed a steady 8000.

With auto ec active the camera will take this action (stopping down) automatically. It will not change ISO because that is already at 100, the lower limit. You can take the shot without doing anything.

In Tv mode you could set a slow shutter speed that requires an aperture that is too small for the lense - f32 for example. Without the auto ec the aperture value would be flashing. With the auto ec function active the camera would automatically reset the shutter speed to the correct value that relates to the lense's actual maximum, eg f22.

Why would you want this? Its a bit like 'green mode' - what you would set when giving the camera to someone who doesn't know about camera settings, but will just be snapping away for a bit. Or if you are shooting in a rapid manner in wildly changing lighting say, and won't have any time to adjust anything.