Processing Sheet Film In A Paterson Orbital

Processing sheet film is a perennial problem, especially for the beginner. The Paterson Orbital tank, designed for processing colour prints, is extremely useful for formats up to 8x10 inches.

Processing sheet film is a perennial problem, especially for the beginner. The Paterson Orbital tank, designed for processing colour prints, is extremely useful for formats up to 8×10 inches. It can take one 8×10 inch or 18x24cm or whole plate; or two 5 x 7 inch/13 x 18 cm/half plate; or four 4×5 inch/9x12cm (or presumably quarter-plate, though we have not tried it).

As the illustrations show, it is essentially a processing tray with a curved bottom and a light-trapped lid. It can be loaded in the darkroom or in a changing bag, after which processing can be carried out in normal room lighting. It is normally used with the domed support base, which is available in two versions, manual and powered, but it can be used without either, simply as a covered, light-tight tray.

Better still, the volumes of chemicals needed are absurdly small, as noted below.




Filling is via the hole on the top; drainage is via the corner marked with the arrow (top left). Both are very quick, a few seconds.The top is clipped in by the ridges, left and right. This is on the power base.

The smaller formats are separated with ‘golf tees’ that are stored in the lid (above and left). Here it holds one sheet of 5×7 and one of 4×5 inch. Note the rough surface on the bottom of the tray.

roughening the inside of the tray

Athough film can be processed in an unmodified Paterson Orbital, it is a good idea to roughen the base so that the film does not stick to it. This has at least four advantages. First, the film is easier to get out. Second, the backing is infallibly removed during processing: without the roughened base, the backing may have to be removed in a separate tray while re-fixing. Third, it allows the film to slip about during processing, greatly reducing the risk of uneven development if the motor base is used. Fourth, there is no danger of chemicals being trapped under partially-stuck-down films, so processing is more consistent and washing is more certain.

We roughened ours (we have two) by ‘kissing’ them repeatedly with a Dremel tool fitted with a small burr. This requires careful washing afterwards to get rid of the debris. We have heard of those who have placed innumerable tiny drops of adhesive on the base, and yet others who have carved deeper channels. All seem to work.




The slight curve of the bottom of the tray is more visible here. The tray will sit flat on the table on the ring that goes over the base.

The snap-on top is equipped with a light-trapped filler aperture and the light trap can be removed (it bayonets out) for cleaning

The Paterson Orbital is no longer available new but turns up frequently at camera fairs and on eBay. Prices vary wildly: anything from a fiver/7.50 euros/$10 or so to ten times as much, or more.


Power base

The power base usually adds quite a bit to the price but it is far from essential and as noted below it can lead to problems with 8×10 inch. It moves the tray in a sort of lurching swirl and is obviously less hard work than agitating by hand. It is also easier to pour the chemistry into the tank while agitating, which is all but essential. The manual version looks similar but is lower and is obviously not powered.





large format without a darkroom

Because the Orbital can easily be loaded in a changing bag, there is no need for a darkroom. Then, there are several kinds of alternative processes which can be conducted under subdued room lighting, making contact prints either by sunlight or via a UV ‘sun lamp’. This allows even those without access to a darkroom to indulge in ‘real’ photography.

It is worth remembering, too, that if you work this way, you will be working with a good deal more precision than most Victorian photographers — and if we were as skilled as the best Victorians, we would be very happy indeed.



This is scanned from a POP (Printing-Out Paper) contact print from a 4×5 inch negative; it was before we got our 5×7 inch cameras. POP can be handled by room light (not fluorescent) and ‘prints out’ without development under sunlight or UV. Processing is restricted to washing; toning (here with platinum); then fixing after toning, and washing again. Roger used Ilford FP4 Plus in his Linhof Technikardan with 210/5.6 Schneider Symmar.

processing sequence

The processing sequence is exactly the same as for any other daylight tank. Fill with developer (via the top); drain (via the corner); add short stop or fixer; drain; wash, either by multiple changes of water (half a dozen changes, each with 30 seconds agitation, should suffice) or with running water.

Developing times of at least 5 minutes are all but essential, in order to avoid uneven development, and for the same reason, developer should be added while the tank is being agitated. With longer development times (8-10 minutes) this becomes ever less important.

chemical volumes


Regardless of the quantity of film being developed, the Orbital requires a minimum of 55 ml (two ounces) of processing chemicals, though most people use a little more: anything from 75 to 150 ml (3 to 6 ounces). With such tiny volumes, ‘one shot’ processing is entirely feasible.

Do not be deceived by those who suggest that this is not enough developer. Most of the developer, in any tank, is used for wetting the film quickly and evenly: the amount of developer that does the work is a teaspoonful or two.

temperature control


The Orbital Processor was originally designed for processing colour prints, so black and white should not be a great problem. The tray has quite a high thermal capacity — it’s a good-sized chunk of plastic — and the developer can of course be brought to the appropriate temperature in a water bath. Even so, we find it easiest to process at ambient remperature, making appropriate adjustments for deviations from the standards of 20 C/68 F or 24 C/75 F.


Agitation must be constant, given the very small amount of developer used. If you want to use it without the base (manual or power), you will need significantly more than the minimum 55 ml (2 ounces) of chemicals. We recommend about twice as much. At three times as much, there is a significant risk of spillage out of the drainage corner.

This is from the original Paterson instruction book and is reproduced by kind permission of Paterson. The manual base is ‘b’ and the instructions say (again by kind permission of Paterson)


power base versus manual

Because the power base has several times produced uneven development (streaking) with 8×10 inch, we strongly recommend that manual agitation be used with this format. We have never seen (or heard of) problems with 4×5 inch or 5×7 inch but we suspect that uneven development may be possible with 5×7 inch. It may be that quantities of developer are critical when it comes to the magnitude of this problem, but we have not done enough tests to be sure. Larger quantities probably make things worse because they flow deeper and faster.




Look to the left of Dean’s face (his right) and you can see streaks of uneven development running parallel with the long side of the negative. This is where the pattern of agitation was too even.



De Vere 8×10, Ross 21 inch (533mm) f/7.7 lens, Ilford HP5 Plus developed in Paterson Universal; print on Ilford Multigrade IV




scanning big negs


If you don’t fancy ‘alternative’ processes such as the one above, negative can be scanned instead — almost any scanner will have enough resolution to make the picture as big as you like.


Holly Lewis

Another 8×10 inch Hollywood-style portrait using the same equipment as for the portrait of Dean (above), but this time scanned using a cheap Agfa scanner with a transparency hood.