Originally Posted by
fillum
...Depth-of-Field (DoF) :- with a crop you are 'faking' the angle-of-view of a longer focal length (FL) but you are basically getting the DoF of the actual lens FL. This may or may not be relevant and really depends on your intent. Shooting field sports for example, you typically want to minimise DoF to separate the subject from the background. A shot taken with a 2.0x TC at 400mm and f/5.6 will show less DoF (i.e. more separation) than a shot taken at 200mm and f/2.8 which is cropped to give the same angle-of-view. [The reduced max aperture will increase the DoF, but the increase in FL decreases DoF by a larger amount, resulting in an overall decrease in DoF]...