I started experimenting with the manual setting on my digital camera. The ISO (International Standards Organization) number is something from film cameras. It’s the sensitivity of the film stock, or the “film speed”. Lower numbers, 100 or 200, are for bright scenes. 400 ISO is good for a cloudy day or indoor. And, the high numbers, 1600 or more, are for night photography –– the higher number let’s you work with less light and as a result has a grainy look. The best image quality comes from using the lowest ISO number.
For digital cameras, ISO refers to the sensitivity of the sensor. You don’t have to switch out rolls of film when you want to adjust the sensitivity. Being able to change the ISO allows greater control of expression. A high ISO number can enable better hand-held photography. So depending on the available light and conditions of the shot, you can adjust the ISO to get the best exposure.
The three factors that control exposure are ISO, aperture, and shutter speed. The aperture refers to the opening inside the lens allowing light to reach the sensor. It’s called the f-stop. It’s called a stop because it stops light. In the early days of film photography, a plate with a hole in it could be switched out from the camera. The smaller the size of the hole, the less light that reaches the film stock.
The tricky thing to remember is that as aperture gets smaller, the f-stop number will get larger. The f-stop is a fraction expressed without the numerator –– denominator being the bottom number in a fraction. So f-8 is a small opening, and f-2 is larger.
For each scene and ISO, the aperture and shutter speed can be adjusted in concert to create the best exposure. When you reduce the aperture opening, the smaller hole requires more time to let in light. If you have the aperture set at f-2 you can use a faster shutter speed. A fast shutter speed helps to eliminate motion blur. At night, you change the shutter speed to allow more light. A tripod keeps the image from becoming blurred.
While experimenting with the camera, I got an image of light reflected on the glass over Grandma’s watercolor of the girl reaching for the sky.