Also, color films intended for daylight snapshots suffered from reciprocity failure
and did not work well with long exposures.
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In contrast, reciprocity failure
was observed in a study of the solar absorptance of space coatings by Olson et al.
They are not only much more sensitive than film, but they are also linear recorders, which means they do not suffer from reciprocity failure
; doubling the exposure time records twice as much light.
The Pro 400 also has an amazingly low reciprocity failure
and excellent response to both red and blue light, its sensitivity to the latter being enhanced by gas hypering.
Because of reciprocity failure
during the 15-minute exposure, the higher-speed film can match the scene in only 30 to 60 seconds!
Like most astrophotographers, I've become resigned to the fact that color films usually exhibit such pronounced reciprocity failure
that doubling the exposure from 20 to 40 minutes renders only marginally more nebulosity.
(Sky fog is a function of f/ratio.) A good rule of thumb that takes into account the reciprocity failure
of modern emulsions is that each decrease of one f/stop allows exposures about three times longer.
Conventional film suffers from reciprocity failure
, which is the emulsion's decreasing capacity to record faint light during long exposures.