Profile correction

[oblivion]

Just going through each setting in Lightroom 4 I was looking at the "enable profile corrections". This is obvious as to what it does.

Having taken a shot using my Canon 55-250mm, I was checking out what the picture would look like with other lens. But when I clicked on "enable" I chose my own lens I took the shot with and it changed the picture? Surely having chosen my lens the picture would stay the same?

 

[gnirtS]

The lens profile correct is there to correct distortion and vignette (amongst other things). So by default your image off the camera (assuming RAW) has none of these. By enabling the lens profile its going into its calibration database and altering the perspecting, lightness and other things to "correct" for lens characteristics or flaws.
In short, yes, you'd expect it to change.

 

[oblivion]

Ahh yes I see. What does it default to from a RAW file then? Does that mean when I shoot RAW I should always be choosing this option and applying the lens I used?

 

[gnirtS]

Depends. Auto will (often) select the right lens. You can set a detault if needed. OR you might not always WANT the correction. Its personal preference.