Please forgive my inexperience in this domain, but I haven't actually ever used one of these.
I would like to know what difference do you make between a converter and an extender, if any?
As a French guy, my technical English is a bit limited, which definitely doesn't help if I want to avoid making any mistake when purchasing the item.
My problem is that I am going in a few weeks time to Africa for a photo safari in a wildlife park and I'm afraid that, although an excellent and powerful lens, my Canon 100-400mm f/4.5-5.6 L IS USM might be a bit too short sometimes.
I've checked the B&H website and found these two ones:
CANON Life Size Converter EF
CANON Extender EF 2x II
There is a 50 USD difference in price, which is not at all a factor in my choice.
I would really appreciate your help in this matter as well as some valuable advice.
Thanks to you all.