Photo Tip Tuesday

Photo Tip Tuesday – ISO, Shutter Speed and Aperture

It is difficult to take good pictures without having a solid understanding of ISO, Shutter Speed and Aperture. While most DSLRs have “Auto” modes that automatically pick the right shutter speed, aperture and even ISO for your exposure, using an Auto mode limits what you can achieve with your camera. In many cases, the camera has to guess what the right exposure should be by evaluating the amount of light that passes through the lens. Thoroughly understanding how ISO, shutter speed and aperture work together allows photographers to fully take charge of the scene by manually controlling the camera. Knowing how to adjust the settings of the camera when needed, helps to get the best out of your camera and push it to its limits to take great photographs.

Let’s quickly review a summary of the ISO, Shutter Speed and Aperture:

ISO – the level of sensitivity of your camera’s sensor to available light. It is typically measured in numbers, a lower number representing lower sensitivity to available light, while higher numbers mean more sensitivity. More sensitivity comes at a cost though; as the ISO increases, so does the grain/noise in the images. Examples of ISO: 100, 200, 400, 800, 1600.

Shutter Speed – the length of time a camera shutter is open to expose light into the camera sensor. Shutter speeds are typically measured in fractions of a second when they are under a second. Slow shutter speeds allow more light into the camera sensor and are used for low-light and night photography, while fast shutter speeds help to freeze motion. Examples of shutter speeds: 1/15 (1/15th of a second), 1/30, 1/60, 1/125.

Aperture – a hole within a lens through which light travels into the camera body. The larger the hole, the more light passes to the camera sensor. Aperture also controls the depth of field, which is the portion of a scene that appears to be sharp. If the aperture is very small (for example, f/22), the depth of field is large. If the aperture is large (for example f/1.4), the depth of field is small. In photography, aperture is typically expressed in “f” numbers (also known as “focal ratio”, since the f-number is the ratio of the diameter of the lens aperture to the length of the lens). Examples of f-numbers are: f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0.

How Do Shutter Speed, Aperture and ISO Work Together to Create an Exposure?

To have a good understanding about exposure and how shutter speed, aperture and ISO affect it, we need to understand what happens within the camera when a picture is taken.

As you point your camera at a subject and press the shutter button, the subject gets into your camera lens in a form of light. If your subject is well-lit, there is plenty of light that travels into the lens, whereas if you are taking a picture in a dim environment, there is not much light that travels into the lens. When the light enters the lens, it passes through various optical elements made of glass, then goes through the lens “Aperture” (a hole inside the lens that can be changed from small to large). Once the light goes past the lens aperture, it hits the shutter curtain (which is like a window that is closed at all times, but opens when needed). The shutter then opens in a matter of milliseconds, letting the light hit the camera sensor for a specified amount of time. This specified amount of time is called “Shutter Speed” and it can be extremely short (for example, 1/8000th of a second) or long (for example, 30 seconds). The sensor then gathers the light based on a pre-defined sensitivity, also known as “ISO”. The shutter then closes and the light is completely blocked from reaching the camera sensor.

To get the image properly exposed so that it is not too bright or too dark, Shutter Speed, Aperture and ISO need to work together. When lots of light enters the lens (such as in broad daylight with plenty of sunlight), lots of light gets blocked if the lens aperture/hole is very small. This means that the camera sensor would need more time to collect the light. For the sensor to collect the right amount of light, the shutter needs to stay open longer for the sensor to gather enough light to produce a properly exposed image.

If the lens aperture/hole was very big, a lot more light would hit the sensor so you would need a much shorter shutter speed for the image to get properly exposed. If the shutter speed is too low, the sensor will get more light than it needs and the light will start “burning” or “overexposing” the image. The overexposed area of the image will look very bright or pure white. In contrast, if the shutter speed is too high, the sensor is not able to gather enough light and the image would appear “underexposed” or too dark.

So, when does ISO come into play and what does it do? Remember, ISO means sensor sensitivity; lower numbers mean lower sensitivity, while higher numbers mean higher sensitivity. If you were to change your ISO from 200 to 400, you would be making the sensor twice as sensitive to light.

Increasing your ISO will allow you to shoot at higher shutter speeds which can allow you the speed to freeze motion. However, increasing ISO comes at a cost – the higher the ISO, the more noise or grain it will add to the picture.

What Camera Mode Should I Be Using?

I recommend using “Aperture Priority” mode when starting out. In this mode, you set your lens aperture while the camera automatically guesses what the right shutter speed should be. You can also control the depth of field in your images by changing the aperture (depth of field also depends on other factors such as camera-to-subject distance and focal length).

What ISO Should I Set My Camera To?

If your camera is equipped with an “Auto ISO” feature (known as “ISO Sensitivity Auto Control” on Nikon bodies), you should enable it, so that the camera automatically guesses what the right ISO should be in different lighting conditions. Auto ISO is worry-free and it works great for most lighting conditions. Set your “Minimum ISO/ISO Sensitivity” to the lowest number available (typically 100 or 200) then set your “Maximum ISO/Maximum Sensitivity” to 800 or 1600 (depending on how much noise you consider acceptable). Set the “Minimum Shutter Speed” to 1/100th of a second if you have a short lens below 100mm and to a higher number if you have a long lens. Basically, the camera will watch your shutter speed and if it drops below the “Minimum Shutter Speed”, it will automatically increase the ISO to a higher number to try to keep the shutter speed above this setting. The general rule is to set your shutter speed to the largest focal length of your lens. For example, if you have a Nikon 70-300mm f/4.5-5.6 zoom lens, set your minimum shutter speed to 1/300th of a second because as the focal length of the lens increases, so do the chances of having a camera shake that will render your images blurry. However, this rule doesn’t always work because there are other factors that all play a role in whether you will introduce camera shake or not. Having shaky hands or improperly holding the camera might cause extra camera shake, while having a lens with Vibration Reduction (also known as Image Stabilization) might actually help to decrease camera shake. Either way, play with the “Minimum Shutter Speed” option and try changing numbers and see what works for you.

If you do not have an “Auto ISO” option in your camera, then start out with the lowest ISO and see what shutter speeds you are getting. Keep on increasing the ISO until you get to an acceptable shutter speed.

Exposure Compensation

Another great feature of modern DSLRs is the ability to control the exposure by using the “exposure compensation” feature. Whether you are shooting in Aperture Priority, Shutter Priority or Auto/Program modes, dialing the exposure compensation up or down (plus to minus) will allow you to regulate the exposure and override the camera-suggested settings. If you find your image (or parts of your image) underexposed or overexposed, you can use exposure compensation to adjust the exposure without manually changing the aperture or shutter speed.

Should I Use Flash or Increase ISO?

It really depends on what you are taking a picture of. Sometimes, it is not possible to use your built-in camera flash in a low-light environment. For example, if your subject is standing far away, you might not be able to reach the subject with your flash. In that case, the only solution is to either move closer to the subject or turn off the flash completely and use a higher ISO. For landscape or architectural photography, you should turn off your built-in flash because it will not be able to brighten up the entire scene. In a low-light situation, the only two options are to either increase the ISO so that you can shoot hand-held, or set the camera to the lowest ISO and use a tripod.

What are “Full Stops”?

Each of the increments between ISO numbers is called “a full stop” in photography. For example, there is one full stop between ISO 100 and ISO 200, while there are two full stops between ISO 100 and ISO 400. The term “full stop” does not just apply to ISOs, the same concept applies to shutter speed and aperture. It is easy to remember full stops between shutter speeds; you start from one and divide the number by two: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, etc. Note: the numbers are rounded (starting from 1/15, which should be 1/16) to make it easy for photography.

Specific Examples and Case Scenarios

Let’s go over what you could do in your camera to properly expose an image in different lighting conditions.

What should I do in low-light situations? Use Aperture-Priority mode and set your aperture to the lowest possible number. Be careful if you have a fast lens such as Nikon 50mm f/1.4, because setting aperture to the lowest number (f/1.4) will make the depth of field very shallow. Set your “Auto ISO” to “On” (if you have it) and make sure that the maximum ISO and minimum shutter speed are both defined. If after increasing your ISO you are still getting small shutter speeds (which means that you are in a very dim environment), your only other options are to either use a tripod or a flash. If you have moving subjects that need to be “frozen”, you will have to use flash.

What do I need to do to freeze action? First, you will need plenty of light. Freezing action during the broad daylight is easy, whereas it is difficult to do in low-light situations. Assuming you have plenty of light, make sure that your aperture is set to the lowest number (again, be careful about depth of field), then set your “Auto ISO” to “On” (if you have it) and set your minimum shutter speed to a really high number such as 1/500th or 1/1000th of a second.

What settings do I need to change to create a motion blur effect? Turn off Auto ISO and set your ISO to the lowest number. If the shutter speed is too fast and you still cannot create motion blur, increase aperture to a higher number until the shutter speed drops to a low number below 1/100-1/50 of a second.

What do I do if I cannot get proper exposure? The image is either too dark or too bright. Make sure that you are not shooting in Manual Mode and set your camera meter to “Evaluative” (Canon) or “Matrix” (Nikon). If it is already set and you are still getting improper exposure, it means that you are probably taking a picture where there is a big contrast between multiple objects (for example, bright sky and dark mountains or sun in the frame). In this instance, set your camera meter to “Spot” and try to aim your focus point to an area that is not too bright or too dark.

How can I isolate my subject from the background and make the background (bokeh) look soft and smooth? Stand closer to your subject and use the smallest aperture on your lens. If you do not like the bokeh on your lens, consider getting a good portrait lens such as the Nikon 50mm f/1.4 or the Nikon 85mm f/1.4, which is considered to be one of the best lenses when it comes to bokeh.

How can I decrease the amount of noise/grain in my images? Turn off “Auto ISO” and set your ISO to the base ISO of the camera (for example, ISO 100).

Now that you have a better understanding of ISO, Shutter Speed and Aperture, next time, we’ll focus on the more creative side of these settings by delving into light painting.

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