[OM] teleconverter elements..how many is good?

[William Clark]

Hey all,

        I just noticed that my 2 Vivitar MC teleconverters are a bit
different.  I have the Macro-focusing one (7 elements in 5 groups) and a
non-macro one with 4 elements in 4 groups (both teleconverters are 2X).
Which one is better?  I am not sure what an extra group and more elements
give you.  Would the extra group impede light transfer in astrophotography?
Thanks for any help....

-Bill