Definition: Behaviour of light-sensitive material such that its response is not proportional to the total energy of incident light e.g. reducing the working aperture by one stop is not compensated for by increasing the exposure time by one stop. * Encountered mainly in low-light conditions but may also occur with extremely short exposure times. Predictability failure There was a time when most films behaved similarly, so you could be fairly sure that where one 400 speed film started to fail in the reciprocity stakes, other 400 speed films would do so. And this was normally when exposure times were more than a second long. Nowadays, while some 100 speed colour films fail at around 2 secs, others hold reciprocity to over 30 sec exposures. Answer: read the instruction leaflet.
Related Terms: reciprocity law
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