The compact FS-60CB Apo can be upgraded to a 60/600 f/10 quadruplet Apo with this 1.7x Q module. Optically, this version is superior to the FS-60CB ...
This extender is suitable for the Takahashi fluorite apochromats FS-60CB, FS-60Q, FC-76D (both versions), FC-76Q, and FC-100D (all versions). However, it is also compatible with the older Sky-90 and FSQ-106 fluorite models, which are no longer manufactured. Of course, it can also be used with many other devices as a moderate focal length extension.