A friend of mine recently asked about some of the fundamental concepts of photography – you know, the ones that every person who’s decided they’d like to get a little more serious about photography should be aware of. My response ended up being fairly long – probably more than my friend had bargained for. But once someone gets me started on a topic that I’m so passionate about, it’s hard for me to keep a lid on things. Anyways, I figured I’d turn my response into a blog post discussing some of the things every new aspiring photographer should know.
Basic camera anatomy:
I’ll keep this simple and to the point, without getting into the nitty gritty details of how a modern camera works… but basically, cameras consist of a body that houses the image sensor (which is equivalent to film in film cameras), as well as a lens that focuses light into the camera and onto the sensor. Also inside the camera body, lying between the lens and the sensor, is what’s called the shutter. The shutter is essentially a curtain that acts as a gate, opening and closing to either allow light coming in through the lens to hit the sensor, or to block it. Most of the time, the shutter is closed, preventing light from hitting the sensor. When you take a picture, the shutter opens up, allowing the light to pass through the gate and hit the sensor (typically, the period of time the shutter remains open is a fraction of a second, but times of minutes or even hours are often used in certain situations). I’ll add that in many modern cameras, there is actually no physical shutter. In these cameras, instead of having a curtain that controls the light hitting the sensor, the sensor itself turns on and off.
Although this may not be the most technically accurate definition of the term, I find it most helpful in practical terms to think of “exposure” as image brightness. The unit that is used to express changes in exposure is a “stop” (note, this term is used to describe changes in exposure, rather than an absolute exposure value). An increase of one stop means a doubling of exposure, an increase of two stop means quadrupling the exposure, and so on. A decrease of one stop means cutting your exposure in half, a decrease of two stops means one quarter of the original exposure, etc.
Exposure is a function of the three main settings on pretty much any camera, namely shutter speed, aperture and ISO. Shutter speed is the length of time that the camera shutter remains open – in other words, it’s the amount of time that light is allowed to hit the image sensor. The longer the light is allowed to hit the sensor, the brighter the resulting image will be (the higher the exposure). Aperture is simply the size of the opening in the lens that lets light through it, which is controlled by a constricting, iris-like mechanism, usually on the camera-facing end of the lens (this is distinct from the shutter). The higher the aperture value (the measurement for this is “f-number”), the smaller the lens opening, and therefore the less light that is let into the camera. So, for example, setting the aperture to f11 would result in a smaller opening and less light entering the camera than setting it to f8. Finally, the ISO is a term used to describe the sensitivity of the image sensor to light, where the higher the ISO value, the more sensitive the sensor (in a practical sense, this means the more easily the senor can detect light). So, all other things being equal, the higher the ISO, the higher the exposure.
You can think about the relationship between these three aspects as a seesaw, where, to achieve a given exposure, a change in one setting will necessitate a compensatory change in at least one other:
In the image above, A shows a “target exposure”, which is achieved when a perfect balance between shutter speed, aperture and ISO is attained. For the sake of this example, let’s assume target exposure is achieved when shutter speed is 1/50s, aperture is f11, and ISO is 200.
In B, when shutter speed is changed, things are thrown out of balance. In this example, shutter speed has been increased (i.e. faster shutter – e.g. from 1/50s to 1/100s). This causes the seesaw to dip on the shutter speed side. In order to compensate for this and return balance to the system (i.e. to weigh down the right side of the seesaw to get back to the target exposure), either a larger aperture (i.e. a wider lens opening – e.g. from f11 to f8) is needed, or ISO needs to be raised (shifting the pivot point of the seesaw to the left – e.g. from ISO 200 to 400).
In C, when aperture is changed, things are again thrown out of whack. In this example, a smaller aperture is used (i.e. smaller lens opening – e.g. from f11 to f16), causing the seesaw to raise on the aperture side. In order to get back to the target exposure, either shutter speed must be reduced (i.e. slower shutter – e.g. from 1/50s to 1/25s) or ISO must be raised (shifting the pivot to the left – e.g. from ISO 200 to 400).
In the final example (D), a higher ISO is used, and must be compensated for either by increasing shutter speed (i.e. faster shutter speed – e.g. from 1/50s to 1/100s) or the aperture must be reduced (i.e. smaller lens opening – e.g. from f11 instead of f16).
Taking this concept one step further, note that, in each of these cases, you could also use a combination of adjustments to restore balance. For example, going back to B, instead of using only a larger aperture value or only a higher ISO, you could make a partial adjustment to both aperture and ISO.
If you think about this seesaw model in terms of what’s actually happening with the camera, it helps to understand why making such changes would be necessary. In B, for example, if shutter speed has been increased, the light is allowed to hit the sensor for a shorter period of time. In order to compensate for this, you could use a larger aperture, which would allow more light into the camera. Alternatively, you could raise the ISO, which would make the sensor more sensitive to the light. Make sense? Clear as mud?
Some other fundamental concepts to consider:
- A lot of people want to know how to get that blurred background they see in pictures (for example, where the person in a picture is in sharp focus, but the background is completely blurred out). I won’t get into this too much now, since it’s a whole other topic that could be the basis of its own post. But suffice to say, the wider the aperture (i.e. the lower the f-number), the easier it will be to get that blurred background effect.
- When photographing a moving subject, the subject can appear to lack sharpness in the resulting picture, and even to streak across the frame in more severe cases. The way to avoid this is to use a faster shutter speed to essentially “freeze” the subject. The faster the subject is moving, the higher the shutter speed needed. For example, to get a really sharp picture of a flying bird, you’d need a faster shutter speed than you would for a stationary bird.
- When taking pictures without a tripod, shaking of the camera due to hand movement can result in blurred pictures. To counteract this, you need to use a relatively fast shutter speed. For situations where you need slow shutter speeds to get enough light onto the image sensor, you may have to use either a tripod or a lens with image stabilization.
- The “longer” the lens (i.e. the higher the focal length/number of mm), the higher the shutter speed needed to avoid the effects of camera shake or subject movement. There’s a rule of thumb that says the minimum shutter speed needed to avoid motion blur is the inverse of the lens focal length (this applies to unmoving subjects). So, for example, shooting handheld (without a tripod) with a 55mm lens, you would need a shutter speed of 1/55s or faster to get sharp images, while with an 18mm lens, you could get away with 1/18s. This rule changes from person to person, but the main thing to take away from it is that telephoto lenses require faster shutter speeds than wider angle lenses to get sharp images. With a tripod, this rule goes out the window with respect to camera shake. But note, however, that with respect to subject motion, higher shutter speeds are still needed for telephoto lenses, regardless of whether a tripod is being used.
- The higher the ISO, the more sensitive to light the senor is – but there’s a downside to this: The higher the ISO, the more digital noise and loss of detail you get in the image (not to mention other nasty things like loss of colour accuracy).
- When assessing the exposure of a picture you’ve taken on the camera LCD screen, don’t rely on the picture that’s displayed on the screen, as the brightness the screen is set at can cause you to be misled. Instead, rely on the image histogram. You can also use the “blinkies” to help guide your decision on a proper exposure. Blinkies are a feature of many modern cameras, whereby overexposed parts of the image will blink on the screen (assuming you have the correct setting turned on in the camera).
I know this is a lot of information for people just starting out in the world of photography, but I promise it becomes second nature with enough practice. Also, when starting out, I highly recommend you take advantage of the auto modes on the camera, until you’ve gotten a little more comfortable with things. A good approach might be to start in full auto mode, then as you get more comfortable, progress to one of the “semi-auto” modes (such as Tv or Av). The semi-auto modes allow you to control one particular setting (e.g. aperture) while the camera automatically sets the other settings accordingly.