« on: November 25, 2012, 05:06:07 PM »
It is not confusion of those characteristics, but sum of all that make final subject isolation, which OP was asking about. There is only one place (distance from camera) which is in the perfect focus, all other things at other distances are blurred, but if you use longer focused distance or bigger F number or smaller FL the blur is smaller ~ even invisible on the final picture...No, look again, the actual blur of the tower is the same, BUT the tower is much bigger with the 400, you are looking at the effects of perspective in those shots NOT depth of field.Yes - the tower is bigger and blurred part is bigger too - thus better blur in my eyes.
In the extreme smallness, the tower will be one pixel width -> perfectly "in focus" = the worst background blur possible, for me...
Opposite extreme: the tower fills whole background = one gray color around the subject = the most blurred background (little boring thus I do not call this "the best" though still good example of the biggest isolation).
You're confusing what is in the background vs. how much that background is out of focus.
Another example: shooting straight en face with 50/2.8 both eyes are sharp pretty the same, but shot with 300/2.8 = it is easy to say which eye was focused on.