On Tue, Jan 04, 2005 at 07:03:24AM +0200, Boris Liberman wrote: > Hi! > > By now, I use my F 70-210 zoom at 210 mm (long end) which makes it > roughly 315 mm on my *istD to make these shots. It is then 315/5.6 > lens. It seems that even at this focal length, f/5.6 yields > considerable DOF that somewhat spoils my backgrounds... What to do?
The first thing to do is to avoid using confusing terminology. You don't have a 315/f5.6 lens. You have a 210/f5.6 lens with the same angle of view that a 315mm lens would produce on a 24mm x 36mm sensor, but with the same depth of field you would get with 315/f8, not 315/f5.6
