Saturday, August 27, 2011

Adox CHS-50 and Caffenol

Some experiments with Caffenol and Adox CHS-50 Art film; a range of development times. The images were all taken on the same day on 35mm, using an Olympus OM-10 in its default auto-exposure, manual focus mode. A cheerfully sunny day, so some high-contrast images at times.

A single batch of developer to the recipe below - nothing exciting, it's just the standard CCM at 1+1 concentration - was made and the film segments developed at approximately three-quarter-hour intervals; that means that the developer for the 16 minute strip had been hanging around open to the air for perhaps two or three hours. That may or may not be significant.


A point to note is that my sodium carbonate is in the decahydrate form; that means that it needs 2.8 times as much - by weight - as the anhydrous form. If you have the anhydrous form, you will need to use proportionally less than in this recipe; you should also note that it will raise, not cool, the water in which it is dissolved.

The vitamin C is a pure powder from a health-food shop; the coffee is the cheapest 'strong instant' from my local supermarket. The same supermarket provides the soda, from the washing department. My tap water here in the UK is rather hard.

Water at 25C - 800ml
Sodium Carbonate Decahydrate - 54g
Vitamin C - 8g
Coffee - 20g
Water at 20C to make up to 1000ml

Mix in order, allowing the fizzing to subside before adding the coffee. The temperature will be close after the soda has cooled the original water.
Prewash 2 minutes in water, wash after development 2 minutes in water, and fixed in Ilford Hypam 1+4 for 4 minutes.

Images are all scanned with no gain, black, or gamma adjustments to permit comparison of contrast range. These levels have been set for the positive images.

10 minutes:
The images appear slightly underdeveloped in the shadows, but produce acceptable scans.
Contrast range 22-224, gamma 0.8

12 minutes:
The image appears properly exposed - there is good shadow detail under the roof, for example.
Contrast range as for the 10 minute development, but gamma set to 1.0.

14 minutes:
Contrast range has decreased to 35-235; gamma at 0.8.
A high-resolution scan at 4800dpi shows resolution as good as the lens and no visible grain.

16 minutes:
Contrast reduced further: 45-235, gamma at 0.8 again. Still producing an acceptable picture, but the fine detail appears to be soft; this could be a focus issue but I doubt it.

For box-speed Adox CHS-50 35mm (and probably 120 roll) a development time in Caffenol 1+1 (20C) of 12 minutes is probably the best. Acceptable pictures will be produced at anything from 10 to 16 minutes, but increasing the time decreases the available contrast and may cause some softening of detail. I don't have a mechanism to explain this.
It's curious that the decreasing contrast is not due to increasing fog; there is none visible at any development time. Rather, the minimum black level, after inversion, appears to rise slightly. I can't explain this, either...
This does not apply to CHS-50 sheet film, which has a different response and upon which I am still experimenting.