![]() The problem is that each film type is affected by reciprocity failure differently, and, therefore, each require different time compensations when calculating exposure.įuji Acros 100, for example, was one of my favorite films for long exposures because it was not affected by reciprocity failure until exposure times reached 2 minutes or more. The concept is simple enough, but it becomes a bit tricky when applying it to specific film types. Reciprocity Failure and Different Film Types For longer exposures of 1 minute or more, you might need to expose for 2 minutes. If your light meter is giving you a reading of 1 second, you might need to expose for 2 seconds. The most obvious compensation is that you will need to add more exposure time to properly expose the image than your light meter reading suggests. The longer the exposure, the less potent the emulsion becomes over time, and, therefore, the more compensation is needed in order to achieve a proper exposure.įilm that had a particular sensitivity to light at the very start of the exposure will be less sensitive to light after one second, and less sensitive than that after 30 seconds, and still less sensitive than that after 3 minutes, and so on and so on. Over the course of a long exposure, the chemicals in the film emulsion lose their potency and become less sensitive to light as a result. This is no different when it comes to film. ![]() ![]() If you remember from high school chemistry, when a chemical reaction takes place, the chemicals in said reaction begin to be used up and lose their potency in the course of the reaction. So, whenever a film photographer exposes an image, their shutter is setting in motion a series of real chemical reactions that eventually will give you your negative. A film’s emulsion is made up of a layer of silver halide chemicals that react when exposed to light. Well, unlike digital photographers, to be a film photographer is to be a chemist of sorts. So why does this failure occur with longer shutter speeds? Reciprocity failure is what happens when, at longer exposures (generally shutter speeds of 1 second or more), the law of reciprocity (you guessed it!) fails! Ilford HP5Įxposure time compensated for reciprocity failure: 1 minute This is what is referred to as the law of reciprocity, and it’s a law that holds up pretty well for photos taken at normal shutter speeds. For example, if a scene requires a shutter speed of 1/250 of a second at f/5.6 for a proper exposure, a shutter speed of 1/125 of a second at f/8 will produce the same exposure value. You’ll also have some idea of the way in which shutter speed and aperture work together in an inverse or reciprocal relationship. That is, you’ll understand that making a properly exposed image depends on a relationship between two variables: shutter speed and aperture (leaving ISO to the side for simplicity’s sake). If you’ve been in the world of manual film cameras for any length of time, the word “reciprocity” refers to a concept you’ll already be familiar with on a practical level. So, let’s talk about what reciprocity failure is first.
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