is it a crop from the 15mm fisheye ?
Very close! No crop -- that's the full frame from the 8-15, shot at 15mm and minimum focus distance. ISO 12,800, f/4, 30 seconds.
What do you think I have used ?
My first guess was the 50 compact macro, but that takes an E-52 lens cap. My next guess was the MP-E 65, but that also takes an E-52. I don't think it's the 180 macro, which would leave either one of the 100s or that EF-S macro.
At my shot the lens cap is clicked in into two lines of the filter thread. So I think it also counts as attached or not ?
Hmmm...I thought the whole point of these lens caps shots was to demonstrate inferior engineering as evidenced by light leaks. No fair if you're the one introducing the leak!