Regardless of the type of camera you have, there are 3 main things that affect the exposure levels in your image:
- Aperture, or the width of the opening in your lens
- Shutter speed, or the length of the time your sensor or film is exposed
- ISO (sometimes called ASA in film), or the light sensitivity of the sensor or film
These are the three components of what’s often called the exposure triangle.
Most modern cameras have a built-in light meter that can determine recommended exposure settings for an image. Since historically, the ISO was fixed, at least for the duration of a roll of film, most camera settings assume a fixed ISO and adjust the aperture and shutter speed as needed. Once you arrive at a particular setting, if you want to adjust one component, then it’s important to adjust another component in the opposite direction to maintain desired exposure levels. For example, if you want to increase the aperture, the typical way to compensate is to decrease the time that the sensor is exposed by bumping up the shutter speed. Don’t worry: I’m about to explain what each of those functions does and why you’d want to tinker with them in the first place.
As mentioned earlier, aperture is the width of the opening in your lens. Aperture can be confusing at first, because smaller numbers refer to larger apertures, i.e., f/1.8 is a larger aperture than f/11. However, it’s important to get comfortable with aperture, as it tends to have the most obvious effect on an image in most circumstances.
Many photographers refer to an aperture setting as an f-stop (if you want to know the details of this terminology, check out the Wikipedia page). If you ever wondered what it means on a lens where it says “f/1.4” or “f/3.5-f/5.6,” that refers to the maximum aperture of the lens. For zoom lenses it’s common to have one maximum aperture at the wide end and a narrower maximum aperture at the long end; hence, the two numbers.
So why adjust the aperture at all? Aperture controls the depth of field in an image, or how much of the image is in focus. A wide aperture creates a shallow depth of field, which usually means that only the subject is in focus and the background is more blurry. This approach is popular for portraits and closeup work, since such photos typically have a clear, defined subject. In those situations too much detail in the background can be distracting.
Smaller apertures create greater depth of field, where more of the image is in focus. This is popular for landscapes, where most people want a sharp image with details visible throughout.
Like aperture, smaller numbers often imply increased exposure. For instance, if you see “1000” in your viewfinder or set your shutter speed to that value, that means your exposure will last 1/1000th of a second. Believe it or not, this can be plenty of time with sufficient lighting. Exposures that last one second or longer tend to be noted with double quote marks (inverted commas if you’re British), such as 1.5″, 2″, etc.
Playing with shutter speed tends to have more specialized applications than aperture. Photographers adjust shutter speed when dealing with moving objects. If you’re shooting something in motion and want to have the effect of “freezing” the action, you can do that by using a faster shutter speed.
Slower shutter speeds are useful when you want to blur part of an image. If you’ve ever seen a photo of a river or a waterfall where the water looks blurry, the photographer used a slow shutter speed to get that effect. Note that exposures of this length typically require a tripod.
The panning shot is a special case of slow shutter speed. An example of a panning shot is tracking a moving subject where the subject appears to be still and the background appears to be moving and blurry.
Something else to consider with shutter speed is that past a certain point, it’s recommended that you support the camera on a tripod or other support. A rule of thumb I’ve heard is any slower speed than 1 divided by the focal length of your lens should be on a tripod. So if your lens is at 85mm, you can probably handhold any shot with a shutter speed equal to or faster than 1/100 (the closest setting to 1/85 on most cameras).
Some of you might be thinking, “Hang on, does this have anything to do with the ISO 9000 people?” As a matter of fact, it does. The fine folks at the International Standards Organization got together and decided to standardize the light sensitivity of camera sensors. Fortunately, the sensitivity approximates that of various types of film, so the terminology is similar across film and digital work.
The numbering scheme for ISO makes immediate sense: higher numbers mean greater sensitivity. You might wonder: why not have the sensitivity maximized all the time? If you’ve shot film recently, you know the answer to this: more sensitive film produces a grainier image, so it tends to be reserved for low light situations.
The same principle holds for digital images: higher ISO increases the vulnerability to digital noise. For this reason photographers usually prefer to keep ISO as low as possible, increasing it only when available light is limited.
Why all this stuff about film?
You might have noticed I’ve referred to film a few times in this post. You might even ask: who shoots film these days anyway? I do, for one. When I first started getting serious about photography, I kept coming across the idea that shooting film can make you a better photographer. What’s even better is that you can get excellent film cameras for a fraction of the price of their digital counterparts.
I’m not going to go into detail about the benefits of shooting film in this post, but I’ve definitely experienced some of those benefits. There’s a vibrant film community out there, and I’ll probably talk more about my film experience soon.
In this post we’ve talked about how aperture, shutter speed, and ISO affect exposure levels in your images. You’ve also learned how you can apply the exposure triangle to make the most of your photos.
I hope some of the tips in this article have been helpful to you. If there’s one you particularly liked, or you have one of your own you’d like to share, let me know in the comments!
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