I tend to think that Agfa may have been wrong too but my old Agfa film development sheet definitely refers to HP5+ and only the 1+50 dilution is stated as "Not Recommended" For reasons unknown to me the sheet gives times for 1+25 so that appears to be OK for Agfa
When I bought my bottle of Rodinal in 2005 the sheet accompanying that makes no mention of 1+50 being Not Recommended
All very strange. So both sheets refer to HP Plus and not the much older HP5 which was replaced by HP5 Plus in 1989 and I suspect that the difference in the two sheets' statements is covered by only a very short period.
Maybe Agfa changed its mind about 1+50 and HP5 Plus
pentaxuser
