how well does a 2x or 1.4x TC work with this lens?
debating if i should get one of those, or save up for a 100-400
A 1.4TC M2 (those currently on the market) is a good addon for a 70-200mm f2.8 IS L. The lens loses only one stop of light and gains a noticable amount of focal length (up to a 280mm now) whilst still retaining a high level of sharpness and optical quality and with minimal degradation to AF speed and accuracy.
In short its a combo that works very well indeed.
The 2*TC however, whilst still retaining AF, is far more fickle item to use. In short in my experience, I found that whilst it worked with the lens, the AF slowed and became more prone to hunting, but worse the optical quality took a significant drop. In the end it was a combo I used only sparingly a few times because whilst it worked in a pinch it just wasn't that desirable a result.
Far as I know the only 70-200mm that can really take a 2*TC and work well is the 70-200mm f2.8 IS L M2 which with a 2*TC gets to an image quality similar to the 100-400mm at the 400mm mark.
Thus if you are after a 100-400mm type zoom lens go for the 100-400mm L. However if you want a stunning 70-200mm and a good 140-400mm lens then the 70-200mm f2.8 IS L is your need (with its sadly much higher price - you do pay to have that stella 70-200mm f2.8 performance.
