Sometimes deliberate under or over exposure can be desired for mood or creative effect but for the most part, we want our pictures to have just the right amount of light and be properly exposed. Fortunately, for nearly all digital cameras today, we have meters built in that automatically adjust for varying degrees of light and create an automatic exposure. This built in meter will measure the existing light and adjust one or more of the three factors that determine the degree of light and light sensitivity that the camera will record. These three measures are Shutter speed, Aperture, and ISO.
On every camera there is a shutter or curtain that is closed until a picture is taken. The shutter briefly opens when a picture is taken and then closes. The amount of time that a shutter stays open is the shutter speed. The number is generally a fraction of a second. A common shutter speed is 1/125th of a second. To control normal hand shaking during the taking of a photo, a shutter speed of 1/30 or less is recommended. To stop fast action such as sports, faster shutter speed is required. A speed of 1/1000th or less is not uncommon in these situations. In general we refer to 1/1000th as a higher shutter speed. And we use these higher speeds to stop action.
The aperture setting tells the camera not how long to stay open but how large the opening is. In other words the shutter does not have a fixed opening. It can be increased or decreased. The aperture setting is measured in f stops and though it is a fraction, it is normally display as a number. In general, f stops range from about 1.8 to 32. Since they are a fraction, a lower number means the opening is larger and a smaller number means the opening is smaller. An f stop of 1.8 results in a large opening and f32 is a small opening. Aperture controls the amount of a photo that is in focus. If a photo contains both near and far elements, a small aperture such as f32 will allow everything both near and far to be in focus. If you used a large aperture such as f1.8, only a portion of the image would be in focus. The rest would be blurred. Sometimes this is desired to allow attention to just one item in an overall photo.
ISO is the light sensitivity of the sensor setting. It too varies in range, from as low of about 100 to as high as 12800 or more. A lower ISO of 100 will produce higher quality of pictures but requires more light to produce properly exposed pictures. A low ISO is usually used outdoors where there is a lot of light. A higher ISO of 12800 will produce lower quality of pictures but requires less light for properly exposed photos.
Now that we understand the basics of these three camera variables, the real fun begins. Every picture we take requires a combination of a shutter speed, an aperture setting, and an ISO setting. Fortunately, digital cameras have an Auto setting that automatically adjusts each of these settings based on its meters and produces a properly exposed photo. But there’s no fun in just having the camera do all the work. And many times we want a special photo that requires us to set some or all of these three variables manually.
Below are three examples.
The top photo of a girl hitting a softball requires us to set a fast shutter speed to stop action. An automatic setting would have created a blurry effect.
The second photo was shot with a large aperture setting such as f1.8. This aperture setting allows only the flower to be in focus. Our attention is not distracted by items outside the window.
The third photo shows the effect of changes in image quality based on ISO. Remember we increase ISO when there is low light. But it comes at a price. You can see there is more detail and less blurring in the ISO 200 photo than the higher ISO 1600.
1. Go on a photo shoot.
Select subjects, objects, or places that will allow you to illustrate changes in shutter speed, aperture, and ISO. If you have a digital camera create at least 3 images each. Take 3 with changes in shutter speed, take three with changes in aperture, and take 3 with changes in ISO. You will need to change the settings on your camera. If you only have a cell phone camera, take 3 fast moving subject photos, three photos where items are close and far, and 3 photos outside versus indoors without flash. Comment as noted in 2. Refer to your manual to make each change.
- Select one of the best images from your shoot in each category to IST 130 Online on Yammer (you should be posting 3 images total). When you post your images on Yammer, be sure to write Lesson 3, and include some information about when and where your photos were taken, and your explanation of what changes occurred when varying the setting for this photo. If you were not able to varying the settings explain the photo you posted and what you think could be changed in shutter speed, aperture or ISO to improve this photo.
Note: Although you are only uploading two photos to Yammer, do not throw away the unselected photographs from your shoot, as I may ask to see the other photos, for a variety of reasons.
3. Sometime during the assignment week, make a positive or helpful comment under one other student’s image, posted on Yammer.