At the time the film had an unshakable truth. The higher the silver grains were placed in the film, the greater its sensitivity to light and would lower its image quality. The reverse was true, the smaller the grains, the lower the sensitivity to light, but higher image quality.
It is easy to understand, a small silver grain graphite is like a fine to the designer. Lets you draw details, since a thick graphite or heavy grain of silver does not allow this detail. However, it is easy to understand that a larger grain is better able to retain a view of the smaller grain, hence increasing the sensitivity.
As you can see the thing was simple, large grain, grainy and easily with low-light situations were the films of ISO 800, 1600 and 3200. Fine-grained, detailed image without grains but low sensitivity were the films ISO 50, 100, 200.
There were tricks that allowed laboratory using an ISO 400 film and reveal, so it worked more or less like a movie ISO 800 or more was pulled from the film. Nowadays, few people even know what it was, but believe there was and was easy to do. A higher concentration of a chemical, or leave the chemist more time acting on the film has already solved this kind of situation.
At that time, a camera, a camcorder as a Super8, a movie camera Super35mm, all worked the same way as movies and these films had ISO (then called ASA but the values were the same)
Today you can push a button, get in there and change a menu setting to ISO 100 to 6400 from one photo to another smoothly with the film you had to make a movie and put another, not now, press a button.
But how can you change the light sensitivity to the pixels inside the camera are the same? If they remain the same size in the same place and receive no different chemical treatments, how is it possible?
In fact, the ISO is a digital fixed and neither should be called ISO. It has a particular ability to absorb light, which is converted into an electrical signal which is converted into a digital signal. We have a file with the image at the end of the line, but we're not talking about ISO, the silver grains or anything . This whole process is done so that the end result resembles in light of what existed in the film, hence the analogy with the ISO.
The use of the term to call the ISO sensitivity of cameras was an error of camera manufacturers. This was done to make life easier for photographers as they were accustomed to films, but it is a mistake.
In the video world, there in the '80s, popularized when the VHS and Betamax. The video cameras were not ISO. Digital video turned, left the film, tapes are digital media . It realized that there was no parallel between film and digital in a digital environment was the electrical signal and the gain.
The video cameras for increasing the sensitivity has a gain command invoked. The gain is applied in decibel (dB) in case +6 dB is equivalent to an increase in ISO point, +12 dB are two points and so on. There are intermediate values, and +3 dB increase is equivalent to half a point of exposure.
This makes sense because the gain is applied in the same way that the increase in volume in a radio: a signal amplifier. And what was placed in video cameras is a amplifier signal. It stopped using the term and began using ISO gain.
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