Almost nothing ad the Pigriff lenshead on the net (exept for the excellent Exakta site, photobutmore.de)
In particular no details anywhere about how dr.Staeble (or possibly Agfa experts after that company was taken over) designed the lenshead optics.
One can safely assume that the 400 and 600 heads are Fraunhofer anastigmat doublets like the Leitz Telyts that also were designed to fit that system. And the slightly more recent "400T" version is specified as a triplet with flatter field to cover medium format.
Nothing ad the 280. Hence I should perhaps share my experience. While cleaning the innards of the 280mm; I discovered that it definitely is a triplet. But using it after the easy reassembly, its performance turned out to be far inferior to the Zeiss 100-300 that I compared it with. The single coating gives too much stray light (but I have not looked at how the internal blackening has stood up over the years. Tomorrow I will try again
p.