- I was playing with my 50 mm lens with a fstop of 1.8. I wanted to have a very shallow depth of field. The problem was that I couldn't get very close to the subject with the 50 mm lens. When I tired, the lens would not focus. When I pulled back the depth of field increased, and items that I wanted out of focus were now in focus. But, I found that if I moved them in front of the area in focus, they became out of focus much more quickly. In the future I think this will come in handy.