It was super windy and the old 400mm definitely does not have image stabilization. I got lucky during a short lull.
The teleconverter loses 2 stops plus the filter material I had left over from the eclipse. Mercury is at about 1:00. Not great but comparable to the live stream from the Griffith Observatory. I may be alive the next time it’s visible from North America but who knows? Best to grab it while I can.