I came across this effect the other day, and have spent the better part of the last week trying to figure out exactly what is happening.
When photographing two layers, with the foreground in front of the focus plane and the background behind the focus plane, the foreground distorts the background. In-focus subjects are not affected. There also appears to be a slight sharpening effect as well.
Three photos presented:
The phenomenon described :
The background without the foreground:
The same shot with a smaller aperture:
Can anyone explain what this effect is? Does it have a name? Is it limited to certain situations beyond what I described? How can I learn more about this?
Since noticing this, I've started seeing it all over the place, including movies and even the naked eye.