How to choose a teleconverter
https://www.bhphotovideo.com/explora/photography/buying-guide/how-to-choose-a-teleconverter/BI/2446/KBID/3285/SID/DFF/DFF/d50 (https://www.bhphotovideo.com/explora/photography/buying-guide/how-to-choose-a-teleconverter/BI/2446/KBID/3285/SID/DFF/DFF/d50)