Developing large format sheet film in a Paterson Orbital Processor

Having recently moved to the 5x7 inch format and not having access to a darkroom, I found myself needing a way of processing these larger negatives. I'd used a Combiplan Tank for my 5x4 negs and I needed a alternative approach as there were no commercially available daylight tanks available for anything larger than 5x4 sheet film.

Enter the Paterson Orbital Processor! Originally designed for processing sheets of colour paper of various sizes it is also the ideal way of processing sheets of film - up to 10x8 inches! The design is nothing more than a glorified tray with a light-tight lid; with a slightly curved base that once loaded in the dark allows processing in daylight. The standard version comes with a dome-like base that allows manual (continuous) agitation. The Orbital also has a real plus point in that it uses far less chemistry than conventional tanks! More on this later!!

However, the Orbital requires slight modification to ensure smooth, hassle free results. The first image shows the processor fully assembled with one difference; I've replaced the original red seperator pegs with longer, white, plastic screws (these prevent sheets of film floating over the small pegs and impeding on the development process).

The second image shows the modification made to the internal lid; the pair of plastic fins that help keep the paper flat have been removed. They were removed with a hacksaw and the rough edges will be filed down - when I get 5 minutes! Without removing these fins you run the risk of uneven development as the chemistry creates flow patterns on the neg where it swirls around the fins - they might work for paper processing but are a real hindrance to film!


The original Orbital used small red pegs to separate the sheets of paper/film and work fine with the colour process for paper as the fins (now removed) prevented the sheets from floating over the pegs in the chemistry; the amount of chemical required to cover a sheet of 10x8 paper is a measley 60ml so nowhere near deep enough to alow the paper to float. However, I have run tests and have found that the optimum amount of chemistry needed for film processing is between 180 and 200ml. This is still a great deal less than most tanks use - the Combiplan used over a litre of each chemical to process 6 sheets of 5x4. However, this increased amount of chemistry means that the sheets of film can now float! The red pegs suppled are simply too short to stop the sheet film floating up and over the peg, out of its compartment and coming to rest on a neighbouring sheet and causing uneven development. An alternative was needed; plastic M3 screws are ideal and were found cheaply on Ebay for a few quid for 20! They simply push into the holes in the base and are cut in 2 lengths; the screws in the base of the tray are longer than those that fit into the "slopes". If the screws were all of equal length then the lid would not close! Those in the base are approximately 5cms long whilst the shorter ones are about 3cms in length.


The image opposite shows two of these screws in place to allow 2 sheets of 5x7 inch film to be processed.

The other modification is also shown in this image. The base of the tray is smooth and as such film has a tendency to stick to it and this interferes with removal of the anti-halation layer and also prevents even flow of chemistry. The solution often used is to roughly score the base with a "Dremmel-type" rotary tool to create a rough surface; other users simply use a sharp blade to score deep cuts - again to create a rough surface. I wanted something a bit easier/cleaner and so found a pack of clear, self-adhesive, rubber "half-domes"; I think they're intended use is underneath sheets of glass to raise it above a wooden surface (such as a worktop or desk) - again a cheap buy from Ebay! Although self-adhesive I used a small drop of Superglue Gel to make sure they stayed put. The chemicals used have no affect on them and they were positioned in a grid-layout to ensure the edges of every format of film I use was covered.

The final image shows the processor set up for 1 sheet of 5x7 inch and 2 sheets of 5x4 inch film. It is important that film is placed in the tray with the emulsion side upwards; this ensures that the chemistry covers the film evenly.

The Orbital will process up to 4 sheets of 5x4; 2 sheets of 5x7 and 1 sheet of 10x8 inch film.

I use two of these modified processors and both are fitted onto the optional motorised base - lazy I know. But the principle behind this system requires that the tray is agitated continuously and without the motorised base you are literally chained to it; manually twisting and turning the tray! It requies constant agitation due to the small amount of chemistry used - even 200ml is enough to slosh out of the pouring funnel but not enough to cover the film completely when the processor is not being agitated. The motorised base ensures even agitation and allows you to do other things whilst the film is developing!
Chemistry is simply poured out of the edge of the processor marked with the arrow and fills through the vent on top of the lid.

A few users adjust the processing time due to the fact that the film is being constantly agitated - I've tried lessening the development time and have come to the conclusion that the continuous agitation has little impact on development time.