Hello John-- I read your post at the Pentax site regarding Gary Fong's PJ flash modifer. I had orderd one some time ago for the 500 flash. His table for matching the correct modifer to the flash for the 500ftz is listed as "P1", howerever it was too small. I dit return it for exchange for the "P2". Now the new 540 appers to have a larger head than the 500. On Gary's web site you will find the table for the match-up. He suggests if you do not know the correct size then measure the flash head's demensions and send to him for him the correct fit. From memory the range of size runs from "P1 through P4". I find the piece works exceptionally well for its intended use.
