Triangle of Exposure in Photography

October 09, 2013  •  Leave a Comment

The Triangle of Exposure in Photography

Introduction:

Understanding exposure is one of the most essential elements of photography. Expensive cameras can take beautiful pictures by default is a definite myth! You might carry a $10,000 camera in your hands but if you don’t know how to play with your exposure, you cannot click astounding pictures!


There are basically three basic elements of exposure i.e. Aperture, Shutter Speed and ISO. Changing one of them affects the other two. To understand this better, let us consider our camera as a window with two flaps. Now lets relate our exposure elements to this window. Consider Aperture as the size of the window. Bigger the size, more light will enter through it. The shutter speed is basically the time for which the door remains open. More amount of time it remains open, more light will enter the room. Now imagine you are standing inside the room. If you wear sunglasses you will see a darker imagine. Which means you have a low ISO. If you keep the size of the window same and remove your sunglasses, you’ll see a brighter scene. That is high ISO. 


Let us now look into details of each one of them.

 APERTURE:

As we saw, Aperture is the size of the window. When you click the shutter button of you camera, a small hole opens up in your lens. Using an aperture value, you can basically control the size of this opening when the picture is taken.

Aperture is measured as ‘f-stop’ or ‘f-number’ i.e. f2.8, f4, f5.6 etc. Changing from one value to the other either doubles or halves the opening of the lens. Large aperture means more opening and smaller aperture means less opening. Make an important point here that smaller the f-stop number, larger the opening. Which means that f2.8 will result in a bigger opening than f5.6. Which means f2.8 will have more light coming into the lens as compared to f5.6.

Concept of Depth of Field (DOF) and its relation with Aperture:

Depth of field can be either larger of smaller/shallow. Larger depth of field means all of your imagine will be in focus. Shallow depth of field will result in only a smaller area of your picture in focus and rest of the picture will be blurred. If you are taking a landscape photo with nice river and mountains in the backdrop, you’ll need a larger depth of field. On the contrary if you need to take picture of a flower and want everything else in the background to be blurred, you’ll need a shallow depth of field.

Now if you have understood the definition of large and shallow DOF, let us relate them to f-stops. Larger aperture means shallow depth of field. Which means if you want to take picture of a flower with the background blurred, you’ll need to stick with a smaller number of f-stop i.e. f2.8, f4 etc. Now as you will start increasing this number and click the same picture, you’ll start noticing that the background has started to get visible. In short, you are moving from a shallow DOF to a larger DOF.

Let us compare set of pictures so you’ll see this with a better perspective. The two pictures below illustrate how DOF changes with aperture value. You can clearly see how the background is visible at f40 and blurred at f3.5

Aperture v/s DOF

Let us look at a few more pictures and their relative f-stops.

Monument Valley Utah, f22
Monument Valley, Utah; Aperture f22


Bleeding Heart; Aperture f4

The topmost landscape picture is shot at f22 because I needed a larger depth of field. That way I have all of the objects in the frame clearly in focus. On the contrary the ‘Bleeding Heart’ picture above was shot at f4. This was because I needed a shallow DOF. In other words, I only wanted the flowers to be in focus and everything else in the background blurred. There were bunch of green bushes in the background but they have been blurred because of the aperture value I chose. That way I kept the viewer’s interest locked on the flowers. A visible busch in the background would have been a distraction.

 SHUTTER SPEED:

As discussed in our opening paragraph, shutter speed is the time for which the flaps on the window remain opens. In other words, the time for which the shutter remains open. Shutter speed is calculated in terms of fraction of a second or seconds i.e. 1/10, 1/500, 1/1000, 2 secs, 5 secs etc. Remember larger the denominator, faster the shutter speed. And faster shutter speeds means better freeze of the action. Acceptable action freeze happens at 1/60 shutter speed. Anything below that (1/10 etc.) will result in shaking of the image. If you want to freeze a biker or a moving car, you will need a higher shutter speed, somewhere around 1/200 or higher.

Let us now look at the relation between aperture and shutter speed. Imagine the amount of light that will enter through the window. Say you have a higher shutter speed. Which means the flaps on the window open and close pretty quickly. So there is a pretty thin margin for the light to enter into the room. Now what will happen when you keep the shutter speed same as before and increase the size of the window? Obviously more light will enter into the room. In short to get the same exposure out of a picture, you have to simultaneously adjust shutter speed and aperture i.e. if you increase your shutter speed by one stop, you’ll have to decrease your f-number by one stop as well. For example, say you clicked a picture at 1/30 and f5.6. Now say you increased the shutter speed by one stop to 1/60. Now you are keeping the opening of the lens same but keeping the shutter open for a shorter time, hence less light would enter the camera. So to compensate and allow the same amount of light into the lens, you’ll have to increase the opening of the lens. In other words, switch from f5.6 to f4.


 Let us now look at a few examples of shutter speed and its application.

Fishing Eagle; Shutter Speed: 1/1000; Aperture: f5.6

In the picture above, I wanted to freeze the action when this eagle picked up a fish from the water. A higher shutter speed of 1/1000 did a perfect job. The aperture was kept at f5.6 so that the bird is in focus and the background is decently visible (Remember here my focus is the bird and not the background. So I wouldn't mind blurring the background a little bit).

Badwater Basin; Shutter Speed: 1/2 sec; Aperture: f22

While taking this picture at Death Valley National Park, I was not worried about freezing any motion so I stuck to a lower shutter speed of 1/2 sec. Also, as this is a landscape picture I needed a larger DOF hence I chose an aperture value of f22.

After shutter speed let us now get to the final element of exposure i.e. ISO.

ISO:

As we saw in the introduction, ISO is the amount of sensitivity to light by your camera. If you leave your camera on Auto ISO, darker the environment, your camera will try to push the ISO to a higher value. Although a very important factor to note here is that higher ISO values lead to a grainy/noisy image Every photographer always strives to keep the ISO value on the camera as low as possible.

There are several situations when you’ll feel the need to push your ISO to higher values like an indoor sports event, museums, indoor concerts etc. In a darker scenario if you want to keep a low ISO (to avoid grainy image), you’ll have to compensate on shutter speed and aperture. Lower aperture values will give you better results with acceptable ISO. Similarly lowering the shutter speed will also yield better results. Although lowering shutter speeds wouldn't work in many situations. Imagine you are shooting an indoor sports event and you don’t want to have a higher ISO value. In that case you will have to lower your shutter speed as well.  But then shooting a fast moving basketball player with lower shutter speeds will result in a shaky image. Hence in situations like these keeping a lower aperture value is the best alternative. All lenses have a minimum f-stop value that you can use. Lower the aperture value, more expensive the lens (Because you can use that lens in a better way in low light situations). For example, a 50mm f1.8 lens is more expensive than a 50mm f2.8 lens.


Here is an example of a low ISO night image:

Brooklyn Bridge; Shutter Speed: 30 sec; Aperture f16; ISO 100

The above picture of Brooklyn Bridge was taken at ISO 100. Because of that, the image turned out to be noise/grain free. But to achieve that, notice I had to use a shutter speed of 30 sec. If I would have used a shutter speed of 1/500 and kept the ISO 100 and aperture f16, this image would have been an extremely underexposed image, almost dark. To make the image visible, I would have had to raise the ISO. But again higher ISO means more noise. Again, since the shutter speed was 30 sec, I had to use a tripod to get this shot. If I had tried clicking this hand held, it would have been a shaky image.
 
Conclusion:

To sum things up, the world of exposure entirely revolves around three elements; Aperture, Shutter Speed and ISO. Each of them is inter-dependent on the other. Changing one element hampers the performance of the other; hence it is important to understand the balance between values of all three. Every photographer strives to come to an acceptable shutter speed, aperture and ISO, which would give him/her a perfectly exposed shot. With my personal experience, I would say you would understand these elements in a much better way when you’ll go out with your camera on field and try different settings. Try an indoor sporting event or a night shot. Try the same shot with different settings and see how your output varies. Every camera has an inbuilt digital meter which shows you whether your shot is under or overexposed. Adjust your settings until you get a perfectly exposed shot.

Exposure/Light Meter

Note that the meter runs from -2 to +2. A perfectly exposed shot will have the scale at 0. Minus values represent underexposed shot while the positive values indicate an overexposed shot. 


So don't wait! Get out there with your camera and play with it! That is the best way to have fun and learn at the same time! I hope you liked reading my post. If you have any feedback or questions, please feel free to write to me at pnbhosale@gmail.com. Happy clicking and happy learning! 

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