I've used both of these films a little; APX25 is an extremely fine-grained film with a fairly 'soft' exposure characteristic, a classic. APX400 is pretty sharp but (to my eye) more grainy than other ISO 400 films like Tri-X and HP5+.(posted 9451 days ago)I processed these films in dilute Xtol (1+2), exposing at the rated ISO.
My impression was that APX25 is a fairly unique and excellent emulsion, while APX400 wasn't as interesting to me.
Dana K6JQ Dana@Source.Net