Oh, I forgot to add how I got my times. I found the exposure time for the couch picture by finding the exposure at F/16. The exposure was 4seconds @ F/16. I used my aperture chart and saw that f/512 was 10 stops under f/16, so I added 10 stops to 4 seconds. That's what gave me about 70 minutes. Actually, I came up with a little more than 68 minutes, but I rounded up