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{For more help on getting started with film, check out the Beginner’s Guide to Film Photography} You all probably have a good grip on exposure by now, and how it is an interplay of aperture and shutter speed used to control the amount of light that hits the film. In case you don’t, or rather for the sake of refreshing our memories, aperture is basically how much the lens opens to let the light in and is measured in f-stops, and shutter speed controls the amount of time the film is exposed for, and thus is measured in seconds. What is Reciprocity Of course, to understand what reciprocity failure is, you must first know what reciprocity is. This is a law, or rather a formula, that says that aperture and shutter speed are inversely proportional. This means if you are letting a little light in, you will need to let it in for longer in order to get proper exposure. Thus, as you keep decreasing the aperture, you will need to keep increasing the shutter speed by the same amount to get the same exposure. You can essentially get the same exposure at various combinations of f-stops and shutter speeds as they compensate for each other to get the right amount of light on the photo sensitive materials. {Image Credit: Florida State University} Reciprocity Failure Okay, so this should make it clear what reciprocity failure is; in simple terms it’s when the aforementioned reciprocity breaks down and is, big surprise, a fail. This happens when you decide to take your camera for a night time walk, or whip it out in any other low light setting, and the shutter speed goes up to a few seconds. The normal rules of reciprocity no longer apply, and a longer length of exposure is needed to get a proper exposure. This means that if you lop the f-stop in half, doubling the exposure time might not work, and extra time would be needed. To get a little more technical on you, when lesser light is available, the silver halide grains in the film are not evenly struck by photons, and the density of the resulting shot is lowered. Basically the film stops responding to light that well. However, each film is different and so the cut-off point for the shutter speed at which reciprocity failure would occur depends on the film you’re using, but usually it is 1-3 second. {Image Credit: Florida State University} The photographs that result from reciprocity failure in B&W film are of lower density with non-existent shadows. In color and slide film, you will see funky color shifts as a result of the uneven light reactions and the different ways each color layer reacts. The exact colors you will see will depend on the particular film you’re using. What To Do About It? Let’s be honest, reciprocity failures can be a pain, especially when you’re using film and only realize what’s happened when the ghostly picture starts to appear in the depth of your dark room. It’s not fun to realize you just wasted all that time and effort with long exposures and what not, so how can you fix this? The answer is compensation. Photography might be an art, but there is also a level of science to it, mainly physics and chemistry. Quite simply, for B&W films you can just increase the exposure time as required to get the desire exposure. Lowering shutter speed to let more light in is your best bet, since playing with the f-stop can mean compromising on depth of field and image sharpness, and so the quality of the shot, and that kind of defeats the whole purpose. Compensations also need to be made post production by developing for a slightly lesser duration. The films you buy should come with charts and formulas to help you figure out exactly how much you would need to compensate. For colored films, increasing the exposure time also works, but color filters also need to be applied to fix color shifts. Again, user data supplied along with the particular film can help out. But why compensate with less developing time when I already increased the exposure time, you say? Well you do need to compensate your compensations. With increased exposures come stark white highlights, as they have had too much exposure time. You need to get some details into these areas and so, decreasing the developing time can help achieve this. Conclusion So with this new-found information, you can walk out into the night without fear. Another little tip to avoiding reciprocity failure issues is to get a film that allows for longer exposures without reciprocity failures coming into play. As all films have different cut off points, certain films perform better in lower light scenes than others. For B&W shoots, Fuji Across 100 is recommended. But most of all what I recommend is to just have some fun with it. Photography shouldn’t get you so uptight, sometimes even failures can be a success and create something unique and beautiful, as long as you know the strengths and weaknesses of your camera and film and have enough control and know-how to recreate an effect!