The Right Amount of Light – The Exposure Triangle
It probably goes without saying, but the one thing you need to capture an image with your camera is light. But how much light do you need to create a photograph? How do I know how much is too much, or not enough? And what the heck is a stop?
A “stop” or “f-stop” is just a unit of measurement like a mile or foot, etc, so when it comes to cameras, it’s a “stop.” Your camera can change a stop or 1/2 stops or 1/3 stops to get the “perfect” exposure.
Think of “exposure” as just the right amount of light on the camera’s sensor to generate a picture. Too little light and it’ll be too dark. Too much and it’ll be too bright. You can use use the “exposure triangle” to give your camera the proper amount of light to generate a good image. The “exposure triangle” explains the three settings you can use to add or remove light so you’ll have the perfect picture. The three points of the triangle are Shutter Speed, Aperture, and ISO. What’s really cool is that each of the points affects the light value, or “stop”, the same amount. So for example, I can take away a stop of light with the shutter speed, then add it back but increasing the ISO value a stop, or by opening up the aperture a stop. All of the adjustment values between them are equal, or “reciprocal.”
Everything with photography is about tradeoffs. For example, to get more light on to the camera’s sensor, again to achieve the perfect exposure, you could boost the ISO. You will now have enough light, but at the cost of more “noise” in the image. Noise looks like you have more “grain” (term from the film days) and the image quality is diminished.
Here’s a quick list of pro’s and con’s with each triangle value. Just keep in mind that these are just guidelines, and there will be times where you want things a certain “wrong” way for the image to convey a certain message. I know that sounds vague, but just table that for now and let’s talk about what each point of the exposure triangle does to the image.
ISO – In the old film days, you bought film that was a certain ISO, like 100 or 400, etc. The higher the number, the less light you needed to get the proper exposure. The HIGHER the ISO number, the MORE sensitive the film was. The trade off is that the higher the ISO, the grainier the pictures became. If you wanted very high quality photos, you had to find a way to get more light in the picture so you could use LOWER ISO film. Well with digital cameras, it’s exactly the same, just substitute “noise” for “grain.”
Shutter Speed – If you were to remove your Canon’s lens and click the shutter release button, you’d see the little mirror flip up an instant before you’d see the shutter of the camera “wink.” The shutter is a tiny curtain that opens up for a the set amount of time to allow light to reach the sensor, thus “take the picture.” The amount of time the curtain is open dictates how much light we’re letting into the sensor. The more light reaching the sensor, the less of an ISO value we can use, thus the higher quality image we can achieve. The tradeoff here is that if the subject is moving and we keep the shutter open longer, it’ll be blurry. If we want to “freeze” a subject in our picture, like perhaps a bird flying by, we’d need to use a faster shutter speed otherwise it would be blurry since it was moving while the shutter was open. In this example you would boost the ISO or open up the Aperture to allow you to use a faster shutter speed, again, getting the proper amount of light to expose the image. If you’re taking a picture of a stationary subject, like a landscape for example, you can leave the shutter open as long as you want so you can get a better ISO or Aperture value. Just be sure to understand any movement of the camera will blur the picture as well, so you might have to use a tripod. BTW, there will be times where you WANT to blur a moving subject to show speed in the image, so that’s why I said these are just guidelines and not rules per se.
Aperture – An aperture is just a fancy word for an opening. In this context, it’s the opening in your lens. If you were to look into your camera while taking a picture, you might see the lens “wink” as it’s diaphragm closes down to it’s setting while the camera snaps a picture. The bigger the opening, or Aperture, the more light you’re letting into the camera’s sensor, and the lower ISO value and/or faster shutter speed you can use to achieve the proper exposure. The Aperture’s settings are generally set by a ring on your lens and have a numerical value like 5.6, 8, 11, 16, 22, etc. The tradeoff here is “Depth of Field,” or DOF. The DOF is just a term for how much of the image will be in focus. Imaging a “plane” of focus, and the depending on your settings, the plane of focus will be larger or more narrow. If I need more light, I can increase the lens’ opening, but at a reduction of my plane of focus, or DOF. The strange thing about your Aperture’s settings is that the HIGHER the setting, the SMALLER the opening. So 5.6 is a LARGER opening than 22.
I know that’s a lot of information to digest, so we’ll stop there for now. And don’t worry, all of this stuff will be subconscious before too long. In the meantime, grab your camera, set it on Manual Mode, and play with the ISO, Shutter Speed, and Aperture and see how they affect each other and the resulting pictures of the same subject with different settings.
Back to The Basics – Photography 101
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