Canon 100-400mm f4.5-5.6 IS L v 70-200mm f2.8 IS II L + 2x Extender III

Just picked up a new Canon 70-200mm f2.8 IS L II Lens and was keen to try it out with the Canon EF 2x Extender III.

First things first.

1. It fits. Some have suggested the extender doesn't fit this lens. It does.
2. The AF works fine on the 1D-X body. Unlike using the extender with the 100-400mm L Lens the AF works fine on the 70-200 its quick and sharp. I tried it on the 7D and can confirm the AF is a lot slower - It does a lot more hunting for focus.

So what about image quality?

Here's the 100-400 at 400mm ISO 800 and 1/6 sec f5.6

Here's the 70-200 at 200x2 = 400mm ISO 800 and 1/5 sec f5.6 (The extender reduces the aperture by 2 stops)

Hard to pick the difference.

Here are 2 shots on a tripod at 100% crop this time shooting at ISO 100 1/250 with a speedlite.

The 100-400

The 70-200 with 2x Extender

The 70-200mm with extender doesn't look as sharp as the 100-400mm? But wait.

You will notice the images cover the same area of the map yet one is smaller than the other. The camera body sits closer to the subject when the 100-400mm is being used on the tripod because the tripod foot on the lens sits closer to the body of the camera. The 2x Extender has the effect of putting a spacer between the back of the lens and the camera - pushing the body back. This wouldn't have been the case if I had fixed the tripod plate to the body rather than the lens foot.

So lets do that again. This time the Body is fixed to the Tripod.

100-400mm

 70-200mm + 2x Extender

Can't split them?

Here's a 200% crop side by side. the 100-400mm is on the left. The 70-200mm + 2x Extender is on the right.

So the 70-200mm with 2x Extender on the 1D-X could replace the 100-400mm at full zoom. The downside with that setup is that 250mm the 100-400 is at f5.0 where as at 125mm 2x = 250mm the 70-200mm with 2x Extender will be at f5.6 - Admittedly not a big sacrifice if you can't afford the 2 lenses.

I will be keeping my 100-400mm for now. With the 2x Extender on that I get a 200-800mm Lens and on the 7D (Although I have to use Manual Focus or Live View AF) I get a whopping 1280mm. Even at f11 this is a very credible and affordable Super Telephoto option.