Suppose I have a subject which is 2ft (60cm) deep, and I want it all to be in focus. The depth-of-field tables tell me that there are an infinite number of ways in which I can do that. But suppose also that I want the background to be as out of focus as possible. If the background is 20ft (6m) behind the subject, and I can get 20ft from the subject, what combination of focal length/aperture/distance gives me the depth of field that I want while putting the background as out of focus as possible? Do I use a short focal length close up, or a longer lens at a greater distance, and do I need to use as wide an aperture as possible?
I realise that I can go out and test these things, but I am thinking that someone here must know the theory!
I realise that I can go out and test these things, but I am thinking that someone here must know the theory!