It was literally "a dark and stormy night" but many of you braved the elements to attend despite the weather.
We began by recapping the topics of the last two weeks - that is - using the shutter speed and aperture settings to control the exposure, or the amount of light, used to create the image. Both of these controls have secondary effects upon the appearance of the image.
The shutter speed setting also controls the amount of motion blur that is or is not visible on the image. The aperture setting controls how much depth of field there is, or how much of the image forward and behind the point of focus is sharply focused or blurred.
Various combinations of shutter speed setting and aperture setting will result in the same exposure (same amount of light) but different photographs.
Our modern cameras allow us to make correct exposures and to control the effects of motion blur and depth of field easily using automatic exposure. Or, more accurately, we can use what I call "semi-automatic" exposure. We can choose to emphasize control over motion blur or depth of field and then the camera will make all the other decisions for us.
Let's use an example. Say we are in the playground watching our children on the swings and we want to take a photo that freezes the swing. In other words, we want to eliminate motion blur. To do that we will need to use a fast shutter speed - a short duration. We need control over shutter speed - that is our priority.
We first change the setting or mode on our camera to "shutter priority auto exposure". On a Nikon and other cameras, this is mode "S". On Canon cameras, this is mode "Tv". Then we set the shutter speed setting to a value high enough to freeze the action on the swing, perhaps 1/500 of a second. Then we begin taking photos. The camera meter reads the light, uses 1/500 as the shutter speed and automatically determines what the aperture should be to ensure the right exposure. The camera will then take the photo. Easy! We didn't have to calculate anything.
Now let's say we would like a nice picture of a rose in a garden. There's a lot of other things behind the rose so we would like to blur the background so the rose stands out by itself. We need to control the depth of field, so we need to control the aperture setting - that is our priority.
We begin by changing the mode of our camera to "aperture priority auto exposure". On a Nikon and other cameras, this is mode "A". On Canon cameras, this is mode "Av". Then we set the aperture setting. To ensure shallow depth of field, we need a wide setting, say f/4. Then we begin taking photos. The camera meter reads the light, uses f/4 as the aperture setting and automatically determines the shutter speed setting necessary to ensure proper exposure. The camera then takes the photo. Easy again! We didn't have to calculate anything.
As a photographer, you'll often have to decide what it is that you want to show in your photos to achieve a particular artistic or creative goal. By using these two "semi-automatic" exposure modes, you'll be able to control and predict the outcome of pressing the shutter based on your decisions.
Often we just want to shoot snapshots of people and events. In that case, use the "Auto" or "P" (for programmed auto) exposure mode on your camera. The camera will make all the decisions for you and you'll still get great photos.
During the storm we also discussed some of the many other settings on your camera. Have a look at the class notes and bring your questions to class next week.
Don't forget to take some photos! Check out the auto and semi-auto exposure modes and learn to take control the easy way. Try changing the White balance and ISO setting while shooting multiple images of the same subject. Bring your favourites and share with the rest of the class. Or, upload some of your images to this blog.
Good shooting!
No comments:
Post a Comment