I don't know whether the fiberglass-reinforced body of the SF series is more robust than the MZ cameras, but the SF series certainly feels solid and heavier. The SF cameras can also take the intervalometer data back.
Joe
As I now have a MZ-5n, I am considering selling my SF-Xn BUT I find there are a few things in the SF that are not found in the MZ body: 1/4000 instead of 1/2000; 1/125 flash instead of 1/100; Infrared flash beam on the SF's integrated flash; possibility to use the integrated flash with another flash mounted on the body for the SF; SF easier to handle with big lenses; SF motor 2.2 im/sec instead of 2 im/sec. Have I forgotten anything?
There are two AF focus settings on the SF and one on the MZ. Is the MZ loosing something on that point?
Andre --

