mamiya 645 question

I've seen Vivitar teleconverters for the Mamiya 645 for sale, details say they have a pin for ttl metering. How well would the work for the AFD camera and how good are they in general? Are there any other brands out there any better?

The old style will not meter properly with the AFD cameras, the same as the old manual lenses to do not fully work with the metering on the AF cameras.

As far as the optical performance, I have never used one, so I can't comment.

I have no experience of the Vivitar models but did manage to buy the Mamiya 2x converter at less than 1/3 new list price when Robert White (UK dealer and APUG sponsor) was shifting factory clearance stock. On the occasions when it has been used I have been very pleased with it. It is for the manual focus cameras but may work in stop down mode on the AF cameras. I'm sure RW would clarify if you were interested as they are still listing them.