Archived posting to the Leica Users Group, 1999/11/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> At 09:07 PM 11/30/1999 -0800, Jacques Bilinski wrote: > >So if it is right: "generally yes, but not at long focal lengths and small > >f stops". > > You believe everything you read on the web? What we have been saying is > correct, depth of field is independent of focal length along. Magnification > and aperture determine it. > No I don't believe everything I read on the Web or in user groups for that matter. For one thing there are plenty of conflicting statements on any topic, as there is in this thread. The web site I refered to states: " Note: When using small apertures (say f/16 or smaller), long lenses do result in slightly less depth of field than shorter focal lengths yielding the same image size." Yes, I happen to believe this statement (until such time as someone can convince me otherwise). I recall reading many years ago a rigorous explanation, as to why this 'rule' which many photographers believe to be 100% accurate is only an aproximation (but nevertheless a useful one). It made sense at the time but unfortunately I've long since forgoten the details. Intutively it makes sense to me that the depth of field for the 2 cases might not necessarilly be the same. Take your statement "A 50mm Macro and a 100 macro at the same magnification and aperture will give the exact same depth of field" By the "same magnification" I assume you mean the same magnification in the plane of sharpest focus. Say the 50mm is acceptably sharp X feet closer than the plane of sharpest focus, and Y feet beyond the plane of acceptable focus. The 100 mm would not have the same magnification as the 50mm at these 2 distances, so it does seem reasonable to me that maybe what matters is some king of 'range in magnification' rather than simply a set distance in front and behind the plane of sharpest focus.