>>4351354Basically the more open you get, the depth of field gets shallower. On an SLR lens you can see marks for the different f stops. If you get in focus, at a given aperture, the marks will show what will be in focus, so you can estimate the depth of field. In simpler terms, pinhole cameras make everything in focus all the time, and a wide open aperture will make the background blurry.
