On Tue, 9 Apr 2002, T Rittenhouse wrote: > Actually, a constant f-stop zoom is a variable aperture zoom. The > aperture has to vary over the zoom range to keep the f-stop constant. > Variable f-stop lenses may have a fixed aperture (that is the aperture > stays the same across the entire zoom range), or a stepped aperture > (one that stays the same over part of the zoom range) which allows a > smaller f-stop variation across the entire zoom range but is still > cheaper than a fixed f-stop lens. Basically a fixed f-stop zoom lens > is bigger, heavier, and more expensive than a variable f-stop lens. > Once again as I have pointed out before, aperture and f-stop are not > really interchangeable terms.
So if aperture and f-stop are two different terms, which controls DOF? That is, pretend I'm using my variable-aperture 80-320/4.5-5.6, and that I have the lens set to f8 but zoomed in all the way, causing the viewfinder to display f11. Now, do I get the DOF of f8, or f11? In other words, if I take two shots at 80mm (one at f8 and the other at f11), then crop and enlarge the shots so they approximate a 320mm view, which one of the shots--f8 or f11--will be closer to what I'd get by shooting at 320mm to begin with? chris - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
