How should I develop ISO 400 black-and-white film that was accidentally exposed at ISO 200?
Asked 4/19/2016
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I shot two rolls of ISO 400 black-and-white film with the camera set to ISO 200 by mistake. I developed one roll normally as ISO 400, and I was unhappy with the result. What should I do with the second roll? Should I pull-process it, and how much should development be adjusted for one stop of overexposure?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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I've accidentally exposed two 400 ASA B&W films at 200 ASA
In other words, you've overexposed it by a stop. (See What is the relationship between ISO, aperture, and shutter speed? if you need a refresher on that.) The fix for this is called "pull processing" (the opposite of "push processing", which is used when you underexpose, treating the fill as one rated for a higher sensitivity.
In general, this isn't recommended, as it often reduces contrast and gives a "murky" overall look, but having done it, it's probably your best option. The information for your chemicals should give you recommended pull processing times.
The puzzlement, though, is that you say you developed the film as normal and it came out under exposed. This is surprising, because that's the reverse of what would be expected in this situation.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
10y ago
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If ISO 400 film was exposed at ISO 200, it was overexposed by one stop. The usual correction is pull processing: develop for less time than normal.
A common rule of thumb is to reduce development by about 1 minute for each stop of overexposure, though the best answer is to check your film/developer data sheet for pull-processing times.
Be aware that pull processing is not always ideal. It can lower contrast and give a flatter, slightly muddy look. Still, if you know the roll was exposed one stop over, pull processing is the standard way to compensate.
One note: a roll exposed at 200 and developed normally would usually not look underexposed; if anything, overexposure is generally more forgiving with black-and-white film. So if your first roll looked thin or dark in printing/scanning, the issue may have been elsewhere in exposure, development, or scanning rather than simply rating 400 film at 200.
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