Film Speeds

You may have wondered all your life what the difference is between different film speeds and why one is better than another. What you’ll actually discover is that no single film speed is best for all applications, and that the various speeds aren’t just improvements upon each other. Each one has its own purpose in film photography. To see film speeds explained, read on.

When you look at ISO film speed, what you are really seeing is a correlation between the different speeds and their sensitivity to light. For example, the difference between film speeds of ISO 100 and 200 mean that the latter is twice as sensitive to light as the former. What this translates to is that you only have to open the shutter half as long to produce the same image. The “speed” equates to the length of time the shutter has to be open. In other words, ISO400 speed film only requires the shutter to be open half as long as ISO200 and a quarter as long as ISO100.

The ISO film speed was derived from the original calculation of ASA film speed, released by Kodak in the 1940s as the standards. Each film speed works best for a different application, and while a higher film speed will create a tolerable image for almost any application, there are times when you can get a better print from a slower speed. For example, ISO100 is the perfect choice for general use in bright light. Because it’s slower, the print comes out in clearer, better detail.

Faster film speeds incorporate greater amounts of silver filigree, which causes a grainier appearance in some cases. However, in lower levels of light, it is necessary to incorporate these for greater clarity. For an indoor application with no motion, you can use ISO200, which will double the sensitivity to light without becoming overly reflective and grainy.

If you are filming motion, ISO400 is a better choice because the speed at which the image is captured will keep the photo from being blurred by the movement. The best film speed for underwater shots is debatable, since ISO400 is sufficient but ISO800, which is faster and requires even less light, will give you the ultimate capability of catching a clear image through cloudy moving water where little light penetrates and you are typically capturing something in motion. Various film speeds are excellent under different circumstances, which is why many digital cameras have adjustable speeds, so that you can get the clearest image in any situation.