How does using a 2x teleconverter with 70-200 f/2.8 affect use?
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.
I have used the exact setup you are using. I found that the 2X Teleconverter iii worked wonderfully with the 70-200 f/2.8 IS II on the 5D Mark iii. I actually tested it in far harder conditions (shooting a wedding in a relatively dimly lit gymnasium) and it worked quite well. Particularly since you will be using the shorter focus distance setting, I wouldn't expect too much problem.
The focus was slower, but not significantly enough that I'd worry about it, even for your use case. Image sharpness was still pristine. It was certainly lower than without the converter, but more than usable. It was far higher quality than my 70-300 f/4-5.6 IS that I was using prior to getting my 70-200 f/2.8 IS II. The consensus here is quite correct, there is a little (but liveable) corner loss, but the center is very clear still.
That said, if you are willing to spend more, the 100-400 f/4L will beat the 70-200 f/2.8 IS II with 2x teleconverter in terms of quality and speed, but it also costs 3 times as much.
For $450 the teleconverter is a great thing to have in your bag of tricks to go with your 70-200 f/2.8 IS II, particularly for the type of shooting you are doing. In fact, the 70-200 f/2.8 II is one of the few zoom lenses I'd recommend the 2x III for because it is so clear. I have to admit I have not purchased one yet, but only because I don't shoot at ranges where I need it often enough and have more pressing upgrades for my kit. Both the 1.4x III and the 2.0x III are on my list of things to get eventually.