Take a look at 3 example screenshots from my Vue 6 Infinite settings and the resulting 4-view windows working with depth of field:

outpostkilanor.blogspot.com/

But like stormchaser suggests to use a postwork effect like in Photoshop or PSPro, it's often much quicker than rendering with a few passes for a long render time.
It's up to the artist to decide, what's necessary - to do it by render or postwork will do ...