The only option for changing the focal length was the Teleskop 1.7x, which as the name suggests, increased the focal length by 1.7x. It's product code is 11.1203, and cost $53 in 1960.
The carrier bracket would also accept the Steritar A, a stereo prism attachment. It gave two vertical images on a regular 24x36 slide. The Steritar A, often marked 812, was product code 20.2004. A matching viewer, product code 20.2801 was available for $12.50. Also available for the viewer was a DC light for the viewer (20.2810 for $12.50) and a transformer to convert the DC light to AC (20.2819 for $7.00)
The carrier bracket could also allow the use of the Contaflex I and II in conjunction with a microscope adapter 20.1616 ($8.00) which also required adapter ring 20.1615 ($3.00).
The Contaflex I and II used the same case as the III and IV, 20.7502. They could also use and right angle magnifier (20.1614 for $17.00), cassettes (20.0300 for $6.00) and take up spool ( 20.0001 for $0.45).
These lenses took S27 (screw in) and A28.5 (slip on) filters, Proxar close up lenses and lens shades.
The 1.7x Teleskop lens
Front and back views of the carrier bracket 20.0200
The Teleskop mounted on a Contaflex II using the carrier bracket 20.0200