I recently acquired the Canon EF 70-200mm f/2.8L IS II USM lens and I love it. However the other weekend I went to Heathrow to do some aviation photography. Whilst it is great for aircraft near to you, for those further away it just needs that little bit more reach!
So I was thinking to get a 1.4x or 2x teleconverter. Probably one of the newest Canon mk III ones.
My camera body is the Canon 5D Mk III.
I know that I'll lose 1 stop of light (therefore making the lens a max f/4 aperture) with the 1.4x tele, and 2 stops (so, f/5.6) with the 2x... However this doesn't bother me too much as in this situation, I'm shooting at f/7.1 and above for a decent depth of field anyway.
I've heard that using teleconverters can slow down AF - important when tracking aircraft on approach - but would the 5D mk III with it's 61pt AF system be so compromised, bearing in mind I'm using AI Servo mode in this case. Also, what about image sharpness and clarity? Many seem to agree the corners will lose sharpness but what about the main area of the frame?
Basically I'm trying to investigate to see whether getting a 2x teleconverter (thus making my lens capable of up to 400mm at f/5.6) is worth it, or if the cons outweigh the pros.