When I took my very first photography class (gosh...was it really twenty years ago?!), one of the things that made a huge impression on me was aperture. It was exciting to learn that I could achieve the look I desired by changing the aperture.
Per Wikipedia, an aperture is a hole or an opening through which light travels. In photography this is obviously the lens. You've probably seen this diagram before - it's a great illustration of what happens to your lens as the aperture changes. When your lens is "wide open" (i.e. f/1.4), it's letting in a ton of light. Or you can "stop down" to a higher f-stop (i.e. f/11) and there's less light getting through.
The thing to remember about aperture is that the more open it is, the shorter the depth of field. Someone once used an illustration to help make sense of that. Have you ever squinted when you're trying to see something far away? That's how your camera works. When the aperture gets narrow, more of the image is in focus; the wider the aperture, the less of the image in focus.
Now, you can make your camera's sensor more or less sensitive to the light by increasing or decreasing the ISO. Back in the day of film cameras, you would control this by the type of film that you purchased. I typically bought 200 or 400 speed film, depending on whether I thought I'd be taking the pictures primarily inside or outside. The wonderful thing about digital is that you're not locked into a particular ISO for a set number of prints, like we used to be back then. Now you can change the ISO whenever you want. The thing to remember is that the higher the ISO, the less light you need, but the grainier your final image will be. I have an example of an image that I love, but it's quite grainy because I shot it at a high ISO (for the camera that I was using). There are lots of problems with this photo - it has a crazy color cast and like I said, it's grainy, but it's an authentic shot of my husband so I love it.
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| ISO 3200 |
One final note about ISO: did you catch my little caveat up there when I said "for the camera I was using"? Not all cameras are created equal. The above shot was taken at 3200 with my Nikon D40. If I were to take the same shot at the same ISO with my Nikon D7000, it'd be a completely different story. One of the reasons my Nikon D7000 was more than twice as expensive as my D40, was because it's much better at handling low light. So the point is, know your camera. Play around with it at high ISOs and get to know what it does.
Okay, moving on, the final variable is how long the shutter stays open. The longer the shutter stays open, the more light that gets through the lens. So if you have a slow shutter speed at f/1.4 then a ton of light is getting through the lens. If you have a fast shutter speed at f/16, not much light is getting through the lens, right? So of course the trick to getting a nicely exposed photo is finding the right balance between these two things. Fortunately for us, modern cameras make this pretty easy for us. On an SLR camera, there's an exposure meter inside the camera. In my Nikon camera, at the bottom of the viewfinder, there's something that kind of looks like this:
+ | | | | 0 - or maybe like this + 0 | | | | -
That's the exposure meter. In theory, those lines to the left of the "0" mean that the image is over-exposed and those lines to the right of the "0" indicate that the image is under-exposed. I say "in theory" because there are a few other things that can throw the exposure off but for now let's just leave it at that - we can get into the exceptions later. Understanding how your camera is metering and how much light your subject is reflecting back will help you expose your image more accurately.
There is one point I want you to consider. Even though your camera shutter can stay open for a very long time to let in a lot of light, you have to remember that if the camera moves at all, it will make the image blurry. If you're hand-holding the camera, you can only hold the camera so steady. I've always had it in my head that you shouldn't really expect to hand hold the camera for more than 1/60th of a second. But that's probably because I started out using a 35mm camera with a 50mm lens. It's actually relative to the focal length. In other words, if you have a zoom lens, it's easier to hold the camera steady when it's wide open, as opposed to when you're zoomed in. Have you already noticed that? And let's be honest, you as the operator plays a big factor. I think I can hold the camera steadier than some people can. I will frequently brace the camera on myself or on stationary objects around me. This is something you have to kind of figure out for yourself and just be aware of it. I recently attended a class by a renowned but elderly photographer and he admitted that he can longer hold the camera as steady as he once could. So you just have to understand your limitations and what you and your camera are capable of.
If you want to learn more, you can start at Digital Photo School's article about shutter speed.
ASSIGNMENT:
For this week, I'd like you to flip that mode dial to Manual, if it's not already there. Practice exposing the image using the camera's light meter. Change the ISO from something low like 400 to whatever is high, for your camera. Pay attention to the difference in shutter speed and/or aperture as well as the clarify of the images. If you're using a zoom lens, notice the change in shutter speed as you zoom the lens in and out.
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