What is the difference between these two series scopes. There is nothing listed on the website detailing anything.

The Z3 series offers a 3x "zoom range" from the lowest to the highest magnification available on a single, adjustable magnification scope - e.g. 3-9x40.

The Z5 series offers a 5x zoom range, e.g. 2-10x50.

Exactly what optical changes were necessary to achieve the expanded zoom range, I don't know. For many years, it used to be possible to get a zoom range of 3x out of scope with a 1" center tube. Scopes with a 30mm center tube offered a max of 4x zoom range. Just a few years back, Swarowski broke out of that limitation and offered a zoom range of 6x. Nowadays, more and more companies are following suit, and Minox seems to be one of them. Note, though, that not all optical instruments are listed with actual magnifications, so many (cheaper) scopes nominally listed as 3-9, say, will in actual fact be 3.5-8.8 - or something.

- mike