Caffenol: finally, a use for instant coffee!

Hardly believing it myself, it turns out that coffee can act as a film developer. This I had to try. Three different films (XP2 at 400, FP4+ at 125 and HP5+ at 400), all developed at the same time:

• five minutes soaking in water
• 16g Na2CO3 (anhydrous) added to water
• add 10g Vitamin C
• 1.5g KBr (anhydrous)
• 40g Red Label instant coffee
• make up to 1 litre of water
• 1 minute of agitation
• rest for 59 minutes (at 21°C)
• wash, stop, wash, fix, wash

All three films showed negatives of good density. However, it's become clear that my Paragon 135mm f/2.8 and EOS-1 do not agree on metering if I stop the lens aperture down. In fact, it seems to underexpose by a significant margin at f/8. This is completely the other way around compared to my EOS-7D which overexposes by around 1.6 stops. Better light metering is required on my part!