Oh my! Pan F with Tmax Dev. I use that all the time. I looked at the box in which the Pan F was packaged and it recommended EI 50 for 4 min. at 68F. The ISO, time, and temp are also listed on www.digitaltruth.com As for 6 min. at 68F, this is recommended with EI 80. I love Pan F....too bad it doesn't come in 4 x 5 sheets!(posted 8357 days ago)