Back in the dark ages of film, I searched and searched for workable teleconverter/lens combos. They were few and far between! I did finally find a 1.5X that worked very well on a particular 300mm lens...



Even when the optics worked well together, it was difficult with film... ISO 200 was the fastest transparency I'd use... which meant about 1/400 shutter speed at best.

Fast forward to the current century... my 500mm f/4L has worked extremely well with Canon 1.4X II Extender:




In fact, that teleconverter works well in another combo I never thought I'd use... on my 100-400mm II zoom!