Good photography is simply the correct measurement of light. There are three ways light is measured by, the ISO, the f-stop, and the shutter speed. Each of these three pieces must be correctly understood to get the best results. If you don’t understand this article, please see the links for better explanations of how each of these functions work.
The first thing to understand is the ISO, this is how we measure the sensitivity to light. Whether it’s film or digital the sensitivity to light is measured by a number, these numbers span from 25 to more than 8000. The lower the number the less sensitive to light, the higher numbers are more sensitive to light.
What does this mean? Simply put an ISO of 100 is about normal for daylight photography, while giving good quality images. The higher the ISO the more noise or film grain will be visible. If your working in low light you may need a higher ISO to get the shot. Most digital cameras do not go lower than 100 ISO, but some will go much higher.
Here are the most common film ISO speeds: 25, 50, 100, 200, 400, 800, 1600, 3200, 6400, 12800. These are in one stop increments, notice that the numbers double every stop? That’s normal one stop increments. There are also half stop and one third stop increments too, you may see these settings with some digital cameras. Just remember that the higher the number the more sensitive to light and the noise increases too.
The second thing to understand is the f-stop. This controls how much light will be exposed to the film or sensor. Note this only controls how much light will be visible, the shutter speed controls how long the light is seen. The f-stop works in the lens, you can sometimes see it when you look into the lens and press the shutter release button, it opens and closes depending upon what setting you use. Wide open the f-stop may be somewhere as big as f2.8 or as small as f32, it depends upon what your lens can do; you may want to see what settings are available on your camera.
Some common f-stops are as follows going from more light to less light: f2.8, f4.0, f5.6, f8.0, f11, f16, f22, f32. These are full stop increments and there are half stops between each of these numbers. Sometimes half or one third stops are useful to get a more accurate exposure. Remember correct exposure is how accurately we measure the light, more accurate we measure the light the better the quality. The f-stop also controls the depth of field which I will talk about in another post.
The third part of understanding exposure is how long the film or sensor is exposed to light. This is called the shutter speed. Shutter speeds are set by the camera most of the time, values range from a second or more to fractions of a second. Going from slow shutter speeds to fast shutter speeds, common shutter speeds look like this: 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, 2000, 4000. Remember there are half stops and one third stops between these numbers to help more accurately measure the light.
Fast shutter speeds stop motion, while slow shutter speeds will cause motion to blur or camera shake that will both cause blurry photographs. If your photographing a fast moving subject you want a shutter speed fast enough to capture the action. For still life you may want a slow shutter speed while the camera is on a tripod, with a small f-stop to get the best depth of field possible.
Measure your light carefully and your results will be best. Understand how your camera measures light and you will be a master in no time.