Originally posted by Jeff Charles According to the FOV calculator on
this page, multiplying the 31mm distance by 1.4 gives the distance required to get the same FOV with the 43mm. For example, at 10 feet, you'd need to step back about 4 feet to get the same FOV.
I believe you have confused FOV with DOF. Yes, you can change position to get the same DOF, but you will never, ever, ever get the same FOV. The FOV of a 43 is *always* narrower than that of a 31. Stepping back will allow you to fit more of any given subject, but will not change the FOV - meaning you won't be changing the amount of background in the image nearly as much as you will be changing the amount of foreground.
So for instance, taking a picture of a person standing in front of a scenic view, stepping back a little with the 43 will allow you to fit as much of the person as with the 31 from the original position, but you'll never get as much of the view. And the amount you need to step back to get the same amount of person depends on your original distance to that person.