08-05-2010, 01:24 PM
It's not a bug, it's a feature, so to say.
Lenses like your 18-55/3.5-5-6 are called "variable aperture" zooms for this reason.
Also the lens name is reflecting this fact ... the maximum aperture of f/3.5 is only reached
at (or near) the 18mm setting, while f/5.6 is the maximum aperture available at the 55mm settings.
For focal lengths in between, the maximum aperture is somewhere inbetween f/3.5 and f/5.6.
Opposed to this, a "constant aperture" zoom, like the 70-200/4 can reach f/4 at each and every focal length.
... Rainer
Lenses like your 18-55/3.5-5-6 are called "variable aperture" zooms for this reason.
Also the lens name is reflecting this fact ... the maximum aperture of f/3.5 is only reached
at (or near) the 18mm setting, while f/5.6 is the maximum aperture available at the 55mm settings.
For focal lengths in between, the maximum aperture is somewhere inbetween f/3.5 and f/5.6.
Opposed to this, a "constant aperture" zoom, like the 70-200/4 can reach f/4 at each and every focal length.
... Rainer