Forgetting to set the ISO dial on a 35mm camera when changing rolls is something everyone does now and again, and if you’re over or under exposing by a stop or so with print film it’s not that serious as the exposure latitude is so great. However, I recently went from shooting Adox CMS 20 at 12 ASA to a roll of APX100 and forgot to set the ISO dial, overexposing by three stops. The early start and the extra glass of wine the night before might have had something to do with it…..
I’ve done push processing before – exposing 400 ISO film at 1600 ISO and over developed to compensate, but never the opposite – I’d always just use a slower film or an ND filter, so this was going to be interesting.
Standard dev time is 9 minutes in stock Ilford IDll developer, and the general rule is to subtract one minute for each stop of over exposure. So, 6 mins in IDll followed by normal stop/fix yielded this :-
Not bad at all – the images were slightly thin but perfectly useable (I probably wouldn’t have noticed if I wasn’t looking for something). The grain is still very fine – this is the weather-vane. These are scanned on a Plustek 7500 at around 35Mb.
The shadows have suffered a bit, but as I was going to throw this roll away I’m very pleased with the results! This is the sign nailed to the right hand side of the entrance.
APX100 is a relatively modern film so can handle this sort or treatment. Whether the older emulsions would react as well is worth a test one day, but until then if you make the same mistake, try to process it – it may not be that bad!
When it’s possible to get useable images from badly overexposed, underexposed or even very outdated film it makes me appreciate what an amazingly flexible medium this is.
Hope you find this useful, thanks for looking!
28mmf2 
Well done. Impressive result.