What is Film Speed?
My Camera is Digital, I Don't Use Film
Film speed or ISO is related to light sensitivity. The slower the film speed, the less sensitive to light it is. ISO 100 (which is considered slow) is less sensitive to light and has less grain. ISO 800 (which is considered fast) will have more grain and be more sensitive to light. ISO 200 is twice as sensitive to light as ISO 100 and ISO 400 is twice as sensitive as ISO 200. Can you see the pattern developing (just alittle photography humor) here? You will see this 2 X 2 X 2 pattern repeat itself again and again the more you learn about photography.
In a digital photograph, grain is called "digital noise". If you have used high ISO values, you may have seen this "noise" show up in your photographs as single red green or blue pixels scattered about in the darker shadow areas. More and more digital cameras are are using very sophisticated algorithms to reduce noise. This feature is usually activated manually and will double the time you have to wait between exposures. If your exposure was 10 seconds, it will be twenty seconds before you can take the next image. Of course a grainy photograph is better than a blurred one, which can happen if to low an ISO and shutter speed are used.
So how can We use this?
To get pictures with the most detail, those on a clear day you can see forever photographs. Out doors on a sunny day, you would set your ISO to 100. On an overcast day, when light levels are lower, you may need a faster ISO value. 200 or even 400 may be required. To stop action you need a higher film speed. A good rule to keep in mind is the lower the light and the faster the action, the higher the ISO value.
For instance, is you were at a NASCAR race and you wanted to get a stop action shot of one of the fast moving cars. YOU would use a higher ISO value, say 400 with a fast shutter speed. This would freeze the car and the background would be clear and in focus. If you wanted to create a photo depicting speed, you would use a slower ISO value and shutter speed, then pan along with the car while pressing the shutter release. The resulting image will have the car in perfect focus and the background would be blurred. Using film speed effectively, as a creative tool, can greatly improve your digital photography. In certain instances, you may want to induce grain or "noise" into your photographs to give them an "Old Fashion" feeling, especially when you are planning to convert them to BLACK and White or SEPIA. Or if you are trying to achieve the look of some of the old photo papers.
You can also add grain or "noise" in the Digital Darkroom using your Image Editing Software.
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