How to Read the Characteristic Curves in a Film

Reading the characteristic curves in a film relates to the field of densitometry. Densitometry studies how exposure to light affects the density of a light-sensitive material. Most photographers are not experts at densitometry, though having the ability to read the basic information of characteristic curves can be helpful. The curve reveals whether the film has a tendency to get very "contrasty" with exposure, which is useful to know in order to adjust your development times or type of developer.

Instructions

Familiarize yourself with the structure of the curve. Time of exposure is measured on the x-axis, while density of the negative is measured on the y-axis. If the curve ascends from left to right, you are looking at a reversal film that creates negatives, since they build density with exposure. If the curve descends from left to right, this exemplifies transparency film, which creates a positive image and becomes less dense with exposure.

Observe the starting point of the curve of negative/reversal film, which is called the "toe" of the curve. Here, in the extremely underexposed portion of the curve, an increase in time does not create significant amounts of density on the negative. "Would you like to understand digital photography methods that bring professional photographers to where they are today? Well, The Top Secret Photography Techniques would guide you out in doing so. To obtain spectacular images we initially want to look at some imperative photography methods. The most important one I am able to share with you is find out about light. You can come across all the things regarding photography techniques on , The Top Secret Photography Techniques. Each time you uncover about light and in what approach it interacts with the direct environment then your images will get superior..". In technical terms, this length of exposure does not follow the Law of Reciprocity: that increased exposure will result in increased density in a uniform manner. The longer the toe, the smaller the increase in density even as time increases. Therefore, a film whose toe is short in length is useful in low-light situations, while a "long-toed" film is more helpful in higher-contrast lighting.

Examine the "straight-line" portion of the curve. This follows the toe, is where time and density start to form a reciprocal relationship, and is where the most helpful information about the film is found. This area is also called the film's "gamma" and shows the film's "latitude," its range of acceptable exposure values. A very steep slope in this area reveals a film that gains contrast quickly with exposure. In general, transparency films will display a much steeper curve than reversal films, since they are much less tolerant of over and underexposure.

Different films have different characteristic curves, but within each type of film, different curves exist for the type of developer used. This is where understanding a film's gamma is helpful. If a film was overexposed and has a high gamma, it may be useful to obtain a developer that lowers contrast, and will therefore lower the gamma.

Take note of the film's "shoulder," or flattened-out upper right portion of the curve in reversal film. The shoulder reveals how the film responds to extreme overexposure. Once again, the failure of the Law of Reciprocity occurs here: time and density do not have a consistent relationship. Some films may even lose density with extreme overexposure. This is exemplified by a shoulder that, after leveling out somewhat, will begin to dip lower on the y-axis.

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