The standard answer when you ask how to increase depth of focus is to either use a wider lens or to stop down.
I understand the stop down and have proved to myself that it works. However, I have been playing around with different lens focal lengths and I am puzzled because it seems to make no difference.
If I want to fill the frame with an object that is approximately 1 foot tall I can:
- Use a 200mm lens at 12 feet
- Use a 100mm lens at 6 feet
- Use a 50mm lens at 3 feet
- Use a 25mm lens at 1.5 feet
But according to the DOF calculator all of those combinations produce exactly the same DOF.
So why is using a shorter focal length lens always recommended for increasing DOF?
What am I missing?