Before I got a Paterson orbital I used divided trays. I often got overdeveloped edges probably due to over-enthusiastic rocking..One day I found there were a few dead flies floating in the water that I had left in a tray. Out of curiosity I decided to find out how little I could move the tray and still get the flies to move around the tray. I found it was very little indeed. Slowly lifting one corner of the tray no more than 5 millimetres caused enough agitation to do the trick. So this has been my method ever since. I have the Orbital on a flat surface, and place a finger under a corner and slowly raise and lower it a few millimetres. I may repeat this once, or twice. Or may do it just once, before moving on to another corner -opposite or adjacent. I follow no pattern, but keep the developer moving slowly and continuously.
Once I tried vigorous agitation for five seconds every half minute -with nothing in between. I got tide marks of uneven development across the negatives. So I went back to continuous agitation. The tide marks were on 5x7 film, and the developer was D76 1+2. Don't know if Rodinal would have done the same.
Originally Posted by AlanC
I have lifted the edge 10mm or perhaps more.
I keep Orbital usually at shallow water bath. So shallow that Orbital tank does not float. So the gently lifting on corner is easy.
I have somehow developed kind a fear of too little agitation, which has driven me to agitate too much.
I did some testing with my orbital last week to see how much agitation was needed to cover the film adequately. If I use the base and rotate by hand there is a lot of movement round the edges with just a little across the inner sides using 300ml of fluid (tested with used film and the lights on). I experimented for a while and found that the gentle agitation discussed here worked very well with just a small amount of movement needed to cover all four sheets of 4x5 using 150ml of chemicals. The best method of all seemed to be 15 secs of Manual rotation followed by gentle side to side tilting.
In the past I'd simply used constant rotation which usually delivers well enough developed negs.