Failure problem of door b

When using the B-door for long exposure, the problem that is easy to occur is the so-called "reciprocity law failure" that photographers often say. This usually happens when exposure is made with color film for one second or more. Fundamentally speaking, long-term exposure can change the color balance of film, and the appearance of this phenomenon is often difficult for photographers to predict.

Generally speaking, there is no simple way to solve the problem of the invalidation of reciprocity law, so that every shot can be accurately exposed. David Williams, a British photographer, put forward a simple method, which is to "take more photos with a longer exposure time on the basis of the calculated exposure".

Williams pointed out that when making long exposure, it is necessary to record the exposure time and aperture of each photo. In addition, various exposure indexes can be used for Shoot to make up for the deficiency caused by the failure of reciprocity law.

One method is to increase the total exposure, and increase 1/2-1-level aperture for 1-9 seconds exposure; For the exposure of 1-99 seconds, increase the aperture by 1-2; Exposure for more than 1 seconds increases the aperture by 2-3 levels. An index like this means that in general, it can't be regarded as a static thing, especially when different films are used, which should depend on the specific situation.