Photography 101: Session 02

A recap of Session 01: You want a photo that is properly exposed. To get that, many people set their camera to "program" (or "auto") mode. This lets the camera determine what the proper exposure should be, given what you are pointing your camera towards. The camera is automatically setting two things: aperture and shutter speed. In program mode the camera makes those choices for you, which in many cases might be fine. If you are happy with your photos in this setting, there might not be a reason for you to change it. But if you want to take a bit more control over your camera, understanding how controlling aperture and shutter speed will impact your images, you will be able to experiment with greater flexibility and get much more out of your camera. You can do this by simply using one of the other exposure modes your camera hopefully has: aperture priority, shutter priority, or manual. For more information on that, please refer to Session 01. So when and how should you use these other exposure modes?

Aperture Priority: As I mentioned in Session 01, I use Aperture Priority just about all the time when shooting outdoors. Aperture is controlling how much light is coming through the lens. The more light you have coming through the lens, the less light you need to come through the shutter on your camera. This of course is all relative to how much light is available, but the dynamics don't change . . more light through the lens = less light needed through the shutter. You control that light coming through the lens by opening and closing the aperture. I prefer to just keep my aperture as wide open as possible in most situations, so I set my aperture to 2.8. In Aperture Priority, once I set my aperture to what I want (usually 2.8 with my lenses), the camera will now determine the shutter speed for me to get the proper exposure. Because I am letting in the most light possible through the lens, I should be getting the faster shutter speed possible. A faster shutter speed lets less light in through the shutter than a slower shutter speed.

So why do I shoot in Aperture Priority? The main reason is that it optimizes my shutter speed. As long as I have my aperture wide open, I can relax a bit knowing that I am shooting at fast shutter speeds. In most cases a fast shutter speed is a good thing. If people are blinking or moving, a faster shutter speed gives me a better chance of getting a good photo. If I am having a difficult time holding my camera still, a faster speed will help counteract that. This is all especially true when the light is not that strong. If your aperture is not open all the way, you are working against yourself by not optimizing your settings.

Let's say you are outdoors and it is early evening. The sun is setting. Your camera is set in Aperture Priority with an aperture of 8.0 and you are getting a shutter speed reading of 1/30 of a second. That might work for you, but there is a chance that at that shutter speed, you might not be able to hold your camera still, resulting in blur. So now that you have control over your camera, change your aperture from 8.0 to 5.6 to 4.0. That is two stops. Remember those are fractions, 1/4 is a larger number than 1/8, or in other words, you are opening the aperture up, allowing more light to come through the lens. To compensate for that additional light, your shutter speed will need to change: from 1/30 of a second up to 1/60 and up to 1/125. Those are two stops to compensate for the two stops change you just made with your aperture. Because you are in Aperture Priority, as you change your aperture the camera will automatically adjust your shutter speed. Under these conditions you will have better chances of a good photo at 1/125 shutter speed than you would have at 1/30 of a second.

Let's say that 1/125 is still too slow for you considering what you are trying to photograph. Now what? Well your one last option (besides adding a flash) is to up your ISO. Let's say your ISO was set at 200. If you change that to 400 (or one stop), your camera will now adjust your shutter speed up to 1/250 of a second (a one stop change). Raise you ISO up to 800 and you gain another stop, or 1/500 of a second. You have to be careful though, because with each raise in ISO you are possibly introducing more digital noise to your image. Given the choice of a blurry bad image vs. a good one with some noise, I would opt for the noise. Sometimes that can be fixed with software after the fact.

Aperture also affects the depth of field in an image. I won't get into this much here except to say that this is largely affected by the focal length of your lens. Longer focal lengths coupled with a wide open aperture is how you achieve portrait images with a blurred out background. Wide angle lenses will give you a more even focus of foreground and background, good for group photos and landscapes.

Next session will pick up on Aperture Priority and then go into Shutter Priority. Please feel free to post comments or questions.