Controlling Camera Exposure

Today’s modern digital cameras are small wonders. They automatically control focus, sensitivity, exposure, flash lighting and in some cases even try to provide composition automation. Anybody can take perfect exposures at any time and some people never take their cameras of automatic settings. They may even call themselves “Photographers” without having a clue on how to adjust camera exposures. Don’t get me wrong, there is nothing wrong with using automatic settings. However, if you are a “photographer” you want to consider things like motion, depth of field and resolution when composing your pictures. To do that, you need to have some idea about how to manually adjust camera exposures to get the image you want. In this article, we will outline the three basic exposure controls; aperture, shutter speed and sensitivity (ISO) settings. Hopefully, it will help you think about planning your images more during capture and be less afraid to use manual settings. To see my commercial images for sale, just click here.

The first adjustment to consider is aperture. The aperture is the “hole” in the lens created by the lens iris. It mimics the eye in that your iris gets smaller when there is more “light” present. If the iris opening is smaller less light will strike the sensor. In the picture, the bottom lens has the smaller opening. The size of the iris is controlled by adjusting the F-stop. The larger the F-Stop number, the smaller the iris. The smaller the F-stop number will have a larger iris opening. F-stops are logarithmic in nature and each stop will either halve or double the amount of light. In automatic mode, the camera controls the iris, shutter speed and ISO sensitivity. Most digital Single Lens Reflex cameras (DSLR) have semi automatic mode where you can select the F-stop and it will automatically select shutter speed and ISO. Here is why you should care. A smaller the F-stop opening will produce a greater the depth of field. If you want to have the foreground and background in sharp focus you need to have a smaller iris opening or higher F-stop number. This is a decision a photographer needs to make. If I am taking a picture of a flower and I want it to stand out against the background of the trees I will want to use a more open iris to have a narrow depth of field and only have the flower in focus. In most scenic views you want to have maximum depth of field and it is rare that an automatic setting will allow this to happen.

Lens Aperture

The next thing to consider is shutter speed. The shutter speed controls the amount of time the shutter is open to allow light to strike the sensor. The smaller number will let less light in to strike the sensor. Like F-stop this is a logarithmic arrangement. A shutter speed of 1/250th of a second will let light strike the films twice as long as 1/500th of a second. Why is this important? The faster shutter speeds will freeze the action more than a slower shutter speed. This picture was shot at 1/500th of a second to freeze the action of the batter and ball. The faster the action, the harder it is to freeze. To freeze a race car, I might need a shutter speed of 1/1000th of a second or faster.

Freezing the Motion

Sometimes you may not want to freeze the action. This image was photographed at 2 seconds so the shutter was open for two seconds. It was also shot on a tripod and the camera was panned with the image to semi –freeze the image of the deer and fawn. Shutter speed is another creative decision. It is impossible to take a picture like this with automatic settings. As with aperture, most DSLR cameras have a shutter priority setting where you select the shutter speed and the camera will adjust the ISO and Aperture to ensure correct exposure.

Creating Motion Blur

Finally, you need to consider sensor sensitivity. In the old days we used different films with different sensitivities. ISO refers to International Standards Association which sets standards on a lot of things including film sensitivity. This image was shot on film at an ISO of 1600 with no flash. ISO can be adjusted on all digital cameras. Point and shoot cameras may just offer a setting of HIGH ISO and LOW ISO. DSLR cameras use the same numbers we used with film. If the number is lower (100) it will have a finer resolution and “grain” but less sensitivity to light. The higher number will have a higher sensitivity to light. This is also in a logarithmic relationship. You may want to use a higher ISO where you can not use a flash (like this Grateful Dead concert) and still want to be able to take pictures. You may also want to use a lower ISO if you are taking a scenic view on a tripod where you can control all three elements so that you can get the best reproduction possible. There, that’s not so scary is it? So next time you get ready to take some pictures think about if you want to use the automatic settings or if you want to change from a picture taker to a photographer and begin to control your environment.

Setting The ISO Sensitivity