Some people have asked me how I create a black background on the field.. I don't, the flash does.
In this picture, since the closest leaf / tree from the grass blade did not get sufficient light from the flash, its fully black.
When you are at f/22, ISO 100, 1/200s, if the flash does not fire you get a black frame, and if the light falls only on the subject you get perfect subject isolation.
Canon 550D + Sigma 70-300 + Raynox DCR 250.