Tokina 400mm teleconverters?

[Robert Soames Wetmore]

Hello, list-

I’ve seen some recent discussion on the list about some of the Tokina 400mm 
telephotos but have only caught a few of the messages (I usually follow the 
list via the archive which only seems to archive a small percentage of the 
messages for some reason), so I apologize if this issue has already been 
addressed…

Can anyone recommend suitable teleconverters for the lens?  I have the SD if 
that makes a difference – I recently picked one up used.  I see a number of 
Kenko and Tokina doublers / teleconverters available new and used.  Are 
there any restrictions on which ones would work, or recommendations on which 
might be best?

Thanks,

Rob