Conventional wisdom and seat-of-the-pants educated guesses have it that in order to match EI and CI of films developed by standard intermittent agitation and continuous rotary agitation requires about a 10-percent reduction in development time when continuous agitation is used.(posted 8435 days ago)I've found this to be _way_ off for two films.
Background: I usually use intermittent agitation but I have this Jobo thing I somehow accumulated sitting over in the corner, so I decided to do some testing to find out what the development-time difference is.
Jobo recommends a five-minute presoak based on their assumption that it'll give development characteristics similar to intermittent agitation. Phil Davis proved that to be untrue; he found that with such a long presoak different films shift characteristics virtually randomly. He also determined that a short one-minute presoak caused no significant differences in characteristics.
So I set off to figure it out, using a one-minute presoak to avoid airbells, testing HP5+ developed in D-76H 1:1 and 1:3.
The first test was with the usual 10-percent time reduction; the result was that I found the development time for a high-contrast EI 800 push, or about N+2 or so. So the conventional-wisdom 10-percent reduction is _not_ valid with this film and developer.
Eventually I found that a 25-percent decrease in development time was required for an EI and curve match for HP5+ in D-76H at both the 1:1 and 1:3 dilutions.
Also, again contrary to conventional wisdom, there's _no difference_ in curve shape resulting from continuous rotary agitation vs. intermittent inversion agitation. The curves virtually overlap from the speed point out 14 stops. This applies to both dilutions tested, 1:1 and 1:3.
Tonight I ran the first test of Delta 100 in D-76H 1:1; results so far are that a 25-percent reduction in development time gives about N+1, somewhat higher contrast than desired.