Tuesday, 25 September 2012

Black and White Film: Reversal Processing

A query from a reader in Amateur Photographer brought back memories of black-and-white reversal processing in the 1950s and 1960s. The reader, who described himself as a technophobe, was asking about the discontinued Agfa Scala and the still-available Fomapan reversal films. Clearly the readers is not a techophobe if he wants to make black-and-white slides or filmstrips by reversal processing but a neophobe. 'Wet' processing is far more technically involved than using a digital camera.

In the Silverprint website, Foma reversal processing kits are available along with the instructions. Also shown is the Ilford Application Sheet from 2003, Reversal Processing Using Ilford Black & White Films to Make Monochrome Transparencies. This Ilford sheet shows the use of potassium permanganate and concentrated sulphuric acid as the bleach bath. Concentrated or even dilute sulphuric acid is not pleasant to have around the house. I remembered that I had reversal processed Ilford FP3 and Pan F to make slides in the 1950s/early 1960s and that I had not used the permanganate-sulphuric acid bleach. I then remembered where I had found an alternative.

Stanley W Bowler's article, Simplified Reversal, in the British Journal Photographic Almanac 1956 (a 1955 Christmas present) states:

Reversal Bath — also known as the Bleach Bath 
The continued insistence in many published formulae on the use of concentrated sulphuric acid is a very real objection, and one to which the writer subscribes fully, having once been burnt by this acid... 
At the suggestion of Mr A.R. Pippard of Johnsons' laboratory, the following alternative bleach bath was tried: 
  Potassium bichromate [now called potassium dichromate]  5gm
  Sodium bisulphate (crystals)                                        25gm
  Water, to make up to                                             1000cc [ml]
This reversal or bleach bath works perfectly satisfactorily and no perceptible difference has been found between it and the formula made up with sulphuric acid. It is essential, however, that fresh clean crystals of the sodium bisulphate are used for the bath to be effective — the fact that this material will not keep indefintely under any but the best of conditions has precluded its being supplied, as one might have expected, as part of a reversal kit of chemicals.
Similarly, a potassium permanganate reversal bath may also be used, using 2 grammes of permanganate and 25 grammes of sodium bisulphate per litre. It should be noted that this bath may be used once only and then discarded.

Why the Ilford Application Sheet does not include this information I do not know.

So, if the fancy takes you to try reversal processing of black-and-white film, like FP4, you can avoid the use of highly corrosive sulphuric acid.

BJP Almanacs are readily available
from Alibris, Abebooks and eBay

The first page of Bowler's article

Silverprint links for reversal processing


Monday, 10 September 2012

Extra Detail or More Crunch? Nikon D800E

There were useful photographs comparing the Nikon D800 with the 800E in ePhotozine:

There was a discernible difference between the two cameras. In some photographs it appeared that was genuinely more detail whereas in others it seemed there was more ‘crunchiness’ as one would expect from a lack of anti-aliasing. Has Nikon achieved a good compromise whereby they have enough anti-aliasing to get extra real detail while avoiding the artifactual over-crunchiness? I suspect they have. Failure to prevent moirĂ© patterning is the downside. The choice between the D800 and the D800E would now be a difficult decision for me.

Wednesday, 5 September 2012

Dufaycolor - Viewing From The Correct Side

My first proper cameras were both 6 x 6 cm roll fim cameras (2¼" square in old money) and I was desperate to try a colour film. Kodachrome was only available for 35 mm and its unperforated roll-fim equivalent, 828. Any colour film was expensive and the first I bought was a 120 roll of Dufaycolor just after, I think, the factory ceased production. It was handed in for processing at the local Boots shop and eventually came back, as I recall, several weeks later.

The film remained cut into 6 x 6 transparencies, being held up to the light for viewing and stored in a film envelope. 2¼ square projectors were extremely expensive.

When scanners first became available, our photographer was kitted out with a flat-bed and transparency hood (and the horrible SCSI card). Because these Dufaycolors had photographs of family members, I asked him to scan them so that they would be safe from deterioration or loss.

I only remembered that I had not told him something important about Dufaycolor when the scans were done and I looked at them on screen. They were reversed left to right. That's because he scanned them as one does any other film or transparency - looking at them from the shiny side. But Dufaycolor was different - you have to view them from the dull (emulsion) side.

I give links to websites explaining Dufaycolor below, so what follows is a resume. On the film base was printed a very fine pattern consisting of transparent blue and green squares or rectangles and red lines. The method of producing this array (reseau) of red, blue and green (shown in one of the websites) was ingenious and must have been the result of extensive experimentation both with the optimal pattern and the printing (the reseau is not that unlike a Bayer screen used in a modern digital camera)  A normal panchromatic film emulsion was then added. In order to achieve colour separation the emulsion was exposed through the base. In the camera, the shiny side faced the lens, not the emulsion - the opposite of normal. That's why Dufaycolors have to be viewed or scanned from the dull side.

Exposing through the base and the printed reseau brought other problems, especially low transparency, so that a much more powerful projector was needed. Projection also enlarged the reseau and it became visible to the audience in a cinema (a few feature films were made with Dufay 35 mm stock) with anything other than a relatively small screen.

The speed was about 8 ASA (or ISO if you must), about the same as most colour films of the time. 

Dufaycolor soon lost ground to the new, subtractive, colour processes exemplified by Kodachrome.

My transparencies do not appear to have deteriorated to any noticeable extent in over 50 years probably because they have not been exposed to light. Information available does suggest the rapid fading of Dufaycolor transparenies in light, especially in a powerful projector.

A couple of years ago, I re-scanned my twelve transparencies in an Epson V500. One of them is shown below along with details of the reseau scanned from small areas of the transparency.

Dufaycolor 6 x 6 Transparency - probably late 1957

Dufaycolor - magnified to show the reseau. Top is parallel
to edge of film  (left hand side of photograph above)
Dufaycolor - magnified to show the reseau. Top is parallel
to edge of film  (left hand side of photograph, top)

Dufaycolor was a French invention developed — ultimately to little avail — by British companies. I did not realise when I walked the dog past the Spicer's paper factory at Sawton, near Cambridge, many years ago that the plant had been the site of secret work to develop Dufaycolor after Spicers bought the process from Louis Dufay in 1926 and before the greatly improved version was launched in 1931.

I had also forgotten that, according to the BJ Almanac of 1956, each box was coded to indicate whether film from a particular batch needed standard exposure, one stop more or one stop less than the indicated exposure. Why they did not just show the speed rating in BS, ASA, DIN, Scheiner or Weston for the particular batch (i.e. 4, 8 or 16 ASA) I do not know.

My twelve transparencies are my only experience of Dufaycolor. They have created interest in this old additive colour process over the years. But if you have scanned slides and the men have breast pockets on the right and the women are buttoned up the wrong way, you may have found some Dufaycolor transparencies.

Links (well worth reading)