Canon 5D Mark III, Canon 500mm f4 IS II, Canon EF 1.4X III TC, Canon EF 2.0X III TC, Canon Extension Tube EF12 II
1400mm, f11, 1/800 sec, ISO 3200
I finally did a test this morning that I've been intending to do for awhile: adding both of my teleconverters to the 500mm f4 IS II lens. I used the Canon Extension Tube EF12 II in between the Canon EF 1.4X III and Canon EF 2.0X III teleconverters in order to allow them to mate up; the body was the Canon 5D Mark III. I was expecting to lose autofocus and the ability to focus to infinity / long distances but wanted to see what would happen. I mounted the 2X TC to the 500mm lens side and the 1.4X TC to the 5D Mark III side.
I did indeed lose autofocus ability - with this set up it would attempt to find focus but continually hunt without ever finding it. However, switching to manual focus allowed me to focus in on my targets, including a line of trees that was farthest away from me in my line of vision (over a fence and across several streets). I don't know if that means true infinity is still achievable or not, I may give this a shot at the moon to check.
The camera told me I was shooting at f8, but actually was at f 11. I was pleasantly surprised by the image quality. Definitely not as sharp as with either TC by themselves, but to my eye definitely usable. The attached image of a finch on my feeder (distance guesstimated at 30 feet or so) is an example of what I got. This image was processed in Lightroom to correct exposure and minimal other adjustment, no cropping or noise reduction. Interestingly, at the top of the Develop module of Lightroom it said I was at 1000mm (picking up the 2X TC) but in the Lens Correction section it chose the 500mm IS II + 1.4X TC combination.
Anyway, my conclusion is that this combination may not be perfect but it is definitely usable.
Canon 500mm f4 IS II at 1400mm
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