Photography 101: Session 03

Summarizing Aperture Priority, you set the aperture you want and the camera will automatically determine the proper shutter speed for what the camera believes is the proper exposure. If you select the largest aperture your lens offers, you are optimizing your shutter speed relative to the available light. You are allowing the most light to come through the lens, which in turn means less light has to come in through the shutter, resulting in a faster shutter speed. In most cases that is what you want when shooting outdoors. Keep in mind that Program (Auto), Aperture and Shutter Priority modes are all auto exposure modes. If I go out on a fairly bright day and shoot in Program mode, that mode might automatically set my aperture to f8 and shutter to 1/500, and that might be fine for what I am shooting. But what if I want or need a faster shutter speed? Personally I would change my mode over to Aperture and set the aperture to the fastest (most open) I can get it, which for most consumer lenses would be either f4 (2 stop difference) or f5.6 (1 stop difference). That will automatically change my shutter speed to the fastest I can get under the circumstances, or in this case, either 1/2000 at f4, or 1/1000 at f5.6. I personally almost always shoot in Aperture Priority and leave my aperture wide open. So, what about Shutter Priority?

Shutter Priority: Shutter Priority behaves just like Aperture Priority, only now the shutter speed is being set by the user and the camera determines the aperture. Now let me say right up front that I cannot think of a time in my life when I shot in Shutter Priority. I have yet to come up with a need to do so, and my guess is you will not have a reason either; so I am not going to spend much time on it. The only reason I can come up with for why someone would want to shoot in Shutter Priority is if they wanted to shoot a series of images at the exact same shutter speed. Not sure why though. My feeling is if you want to control the shutter speed, do it within Aperture Priority. It will basically give you the same results. Remember, these are both auto-exposure modes, so the resulting exposure will be the same. In Aperture Priority, if you wanted to dial in a specific shutter speed, just adjust your aperture until you get that shutter speed reading. I have found that to be just as quick and easy to do than setting it over to the Shutter Priority mode. My advice: don't worry about this mode.

So that brings us to one last exposure mode: Manual.

Manual Mode:  When you point your camera toward what you are about to photograph, your camera's exposure meter will analyze the scene and determine what it believes to be the proper exposure. In most cases it will be pretty accurate. There are times however when your camera meter will be fooled. Usually it will happen in bright situations, like on the beach or in the snow, or when it reads the sun reflecting off of a window. The camera will read this as way more light than what is really there and will tell the shutter to close down quicker than it should, resulting in not enough light exposing the image. You end up with a dark image.

Let's say you are on the beach and it is really bright out. Now let's say that the proper exposure for these particular conditions would be f5.6 at 1/1000 of a second shutter speed. At the moment we don't know these numbers because we have no way of measuring them up front. We point our camera towards the water and white sand and the camera interprets the exposure as f5.6 at 1/2000 or maybe even 1/4000. In other words it believes there is a lot more light than there really is, so it is not letting as much light in through the shutter as the scene actually requires. The result will be a dark, underexposed image. This is often why snow looks dark blue or our beach pictures look overly contrasty. Not enough light was making it through the shutter to properly expose it. Since the camera is giving us a reading of let's say 1/2000, we need the shutter to stay open a bit longer. So let's try 1/1000. Now, if you bounce around between Program, Aperture or Shutter Priority modes, you will get the same exposure because they are all auto modes. So if you are in one of these modes and you go to set your shutter to 1/1000, you will unintentionally also be changing your aperture to f8. Effectively, nothing has changed in regards to your exposure. To gain control over your exposure settings, you have two options: 1) manual mode, or 2) exposure compensation dial.

If you set your exposure mode to Manual, you will have to set both your aperture and your shutter speed manually. If you know from looking at the monitor on the camera that the settings f5.6 and 1/2000 were too dark, you could then manually set it to f5.6 and 1/1000 and see what happens. For good measure you could even take another shot at f5.6 and 1/500.

Exposure Compensation (EC): Many cameras have some kind of exposure compensation dial. I use mine quite a bit. This dial allows you to stay in Aperture Priority and override what the camera is picking as the shutter speed. Oftentimes I will shoot in a situation where I know the camera is not reading the exposure correctly. It can be off by a full stop, either overexposing or underexposing the image. The EC dial lets me very quickly dial in a compensation for that, either up or down. If the camera is telling me to shoot it at 1/1000 but I want it to fire at 1/500, rather than switching over to Manual mode and dialing in everything manually, I can just turn this dial, basically fooling the camera to accept a 1/500 shutter speed.

I realize that all of this sounds like work, and if it is new to you it probably also sounds confusing. The best thing you can do is hold your camera, read through this and play with the settings. See how the different settings affect your exposure, or not. It's one of those things that the more you use it, the more natural it all feels. And you gain control over your camera, especially in difficult situations. I could tell you up front what to set your camera at in various locations, but that information might not entirely accurate, and you wouldn't understand why. Hopefully this will help.

Coming up next will be a wrap up of exposure, including the different ways your exposure meter works; followed by indoor photography with flash.