The first test exposure with the lens wide open gave an interesting result. The sunspot is reflected in the octagon.
The last time I photographed the "end of the world" was the Transit of Venus back in June of 2012 (https://photoofthedayetc.wordpress.com/2012/06/06/transit-of-venus/). I had a different camera and a 600mm lens back then, and while I don't have a 600mm lens anymore, I still have the Neutral Density (ND) filters I used to photograph the sun in 2012. Tristan reminded me on Sunday that the Transit of Mercury was occurring on Monday, May 9, 2016, and told me I had to photograph it. I dug around my filter box and found the three NDX8 filters. The problem is the NDX8 filters are 58mm, but my 70-200mm zoom lens takes 67mm filters. I did more digging around in my photo stuff, trying to come up with a way to attach 58mm filters to a lens that takes 67mm filters. Tristan and Laurie were quite entertained, and I was about to Duck Tape the filters to the lens when I remembered I had various sized step-down rings for my macro flash. The solution to the filter problem was to tape a 67mm and a 58mm step down ring back to back and screw the three NDX8 filters on the side with the 58mm threads, and then screw the side with the 67mm threads onto the lens. Since the lens hood for the 70-200mm lens didn't fit with the step-down rings on the lens, I adapted the adjustable lens hood off my Bronica 6X7 to marginally fit on the lens.
Next, I walked out into the mid-day sun and tested various exposures. Then I added a polarizing filter to the stack of filters and did some more tests, including exposures through clouds that were passing under the sun. The results are interesting and I did manage to capture a sunspot during the test exposures.
Stack of filters on my make-shift adapter
Test shot with only NDX8 filters
Bronica lens hood precariously attached to the lens
Test shot with the polarizing filter added to the stack of filters
Test shot with NDX8 and polarizing filters and sun covered by a thin cloud
Test shot with the NDX8 and polarizing filters and sun partially covered by a thicker cloud