Interesting thread. Last week I decided to see what I could get at extreme range with my 500mm f/4 (IS II version). I set up my 1D mk IV (APS H sensor so 1.3 crop factor) with my 500mm + 2x TCIII + 36mm, 20mm and 12mm extension tubes + 1.4x TCIII, thus giving effectively 1820mm @ f/8.. I set this up on a tripod and used a remote shutter release:
View attachment 498763
First off I did some tests in my back garden. The first shot below is uncropped on my 5DIII at 50mm (roughly what we see with unaided vision) the target being the writing on the lens box on the wall next to the cat. The second shot below shows a 100% crop of the same image to better show what I was aiming at. The 3rd shot below shows the result from the 1820mm set up. Uncropped and slight sharpening applied only. The distance for the three shots was the same in each case, approx 14 yards:
View attachment 498760 View attachment 498761 View attachment 498762
So then I took this set up out to try on a live subject, in this case a slow moving Canada goose. The subject was approx 120 yds away and I used liveview on full mag to focus manually. I pushed the shutter speed up to 1/5000 sec to offset minor movements in the equipt and again used a remote shutter release. ISO 1600:
View attachment 498764
I don't think the result was too bad considering what I used. I know I could improve it by reducing the shutter speed with a resultant decrease in ISO. When I go out with my 500mm I always carry the two convertors and now I've started carrying the ext tubes to allow the convertors to be stacked as well (you can't stack the sIII TCs without using at least one tube).