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Exposure - Shutter speed, Aperture and ISO

May 21, 2008

When I first started photography 4 years ago, I am having trouble to understand about what is exposure. But after a while I’ve got the idea. Today I will introduce to you what is exposure and I will guide you to a simplified step by step guide on what is exposure and how to use it. This post will be divided into three sections. The first one is the general view about exposure which I have introduced to you just now and the second which I will tell you after this is about the factors or the elements that makes the exposure and the last part of the post will guide you on how each elements of exposure affects each other and how to use them effectively. I will tell you when we arrived at each sections, so relax and don’t worry about asking your self which chapter you at.

What is exposure? It can be simply describe as the combination of right shutter speed, aperture and ISO. Thats it. Simple right? See the diagram below:

It is easy to understand exposure. But the tricky part is the elements that involves in exposure. The shutter speed, aperture and ISO. It is enough for you to understand exposure as the right combination of these three elements. Now we move to the second part of this post, which is what is Shutter speed, aperture and ISO.

The three elements:

So far I have briefed you about what exposure is. Now I will introduce to you the three elements that involves in exposure.

Shutter Speed

Shutter speed is the amount of length the shutter or curtain in the camera opens when you click the trigger. It can be adjusted automatically or manually and of course manual is always better. The longer the shutter speed, more light will reach the camera sensor. But if the shutter speed are so long, the image will get blurred effect. In order to get the sharp image, the rule of thumb is the shutter speed should be same or higher than the focal length. If the lens is set to 200mm focal length, than the shutter speed should be 1/200 or higher and if the lens is set to 50mm, than the shutter speed should be 1/50 or higher. But the normal practice is to keep the shutter speed above 1/60.

you can see the picture above is sharper than the bottom one

You might asking what is 1/200 and 1/60 i mentioned above. 1/200 means the shutter opens 1/200 seconds long (about 0.005 second) It is fast right? The common shutter speed are:

30″, 15″, 8″, 4″, 2″, 1″, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000, 1/8000.

• 30″ means the shutter or curtain will remain open for 30 seconds

• 1/30 means the shutter will remain open for 1/30 seconds (about 0.033 seconds)

At this point, that’s all you need to know about shutter speed.

Aperture

What is aperture? Aperture is the size of opening in the diaphragm mechanism inside the lens. The wider the opening, more light will be exposed to the sensor. Like shutter speed, aperture can be adjusted automatically or manually. It is represented by the symbol of f/numbers (example: f/1.4). The smaller the number the wider the opening. Remember this! the smaller the number, the wider the opening. As more light are exposed when using wider aperture, part of the picture will become blurred. But when you use the smaller aperture the image become sharper but then the image will become darker. Below are the example of the use wider and smaller aperture:

Can you see the difference it makes by using small and wide aperture? In the next section of this post I will tell you when to use wide and small aperture and some practical example. But now we move to ISO.

ISO

ISO is the sensitivity of the camera sensor towards light. The higher the ISO the more sensitive the sensor become. ISO 1600 will require less amount of light tp form a correct exposure while ISO 200 will require more amount of light to form a correct exposure. The normal ISO is 200, 400, 800, 1600, 3200 where the ISO 200 is less sensitive towards light and 3200 is the most sensitive towards light. But still, like shutter speed and aperture, it has some weaknesses. Higher ISO will produce some grain inside the picture. While you get brighter picture, it comes with the price of picture have more grain or noise. See the example above:

You can see the grain or noise at the darker area of the picture.

So far we have covered what is exposure and I have brief you about the elements of the exposure. Now we will move to the last section of this post.

The practical part:

Here I have divided the section into three part.

Shutter speed or Aperture?

So, you may asked, When to prioritize aperture and when to prioritize shutter speed. Since you can get the correct exposure at many combination of both aperture and shutter speed, it is important to know when you want to use small aperture with slower shutter speed or wider aperture with faster shutter speed. Normally it depends on what subject you want to take. If you want to take landscape or panoramic view than the combination of smaller aperture with slow shutter speed is mostly used because these sort of subject requires greater depth of field (what is that?, don’t worry, depth of field will be covered after this). And if you want to take portrait, than the combination of wider aperture and faster shutter speed is normally used. But still it depends on your creativity. The best rules in photography is to brake the rules. That may seem weird. But yes, if you want to be creative or different than, BREAK THE RULE!. These rule is only for your guidance. The camera is yours.

Motion and Shutter speed

You might have seen picture of a car with a blurred surrounding. How to get that kind of effect? simple, go to the road side and shoot the picture. But before that, you have to read this first. With the use of shutter speed, you can freeze the car completely with the surroundings even the tire of the car and with shutter speed also, you can freeze the car but with the blurred surrounding and spinning tires. If you use fast shutter speed such as 1/2000 and above you can freeze a car with its background. But if you turn to shutter speed let say 1/125 or 1/80, you can get the sharp car with blurred surrounding that shows the car is moving fast. But you need to add one more technique, PANNING. Panning is use to get these kind of effects. How to pan? Set your camera to correct exposure. Try panning. Move the camera following the subject (in this case a car) Click the shutter at some point (just after you move your camera) and continue to follow the subject even you have taken the picture until the car disappears and remember to pan at exactly the same speed as the subject. You won’t get it for the first time. this techniques requires trial and error practice so keep shooting until you success.

Depth of field and F-stop (aperture)

We have seen pictures that is so sharp. The subject, the background and foreground are all sharp with details. We also have picture is focused into the subject with the background and foreground out of focus. This effect is called depth of field. Pictures with sharp subject, background and foreground have higher depth of field while picture with the subject is focused and the background or foreground or both is out of focused have less depth of field. So, how to achieve it? One way is, to change the amount of aperture. F/2 will have the effect of only the subject is sharp while the surrounding is out of focus. If you change or stop down the aperture to f/22, than the subject, foreground and background will be fully sharp and into focus.

But there are limitation into what you want to achieve. You will not always get the right combination to get the right exposure and desired results. For example, you want to freeze a n image of a car and get a sharp focused surroundings, you have to use fast shutter speed in order to freeze a car and at the same time to use small aperture ( example: f/11, f/16, f/22) to get sharp focused surroundings. Bu this two settings will produce darker picture. One way to counter this problem is to use ISO to get the sensor more sensitive towards light. Perhaps you have to use ISO 800 or 1600. You get a freeze car with sharp focused surrounding with correct exposure BUT, the picture will have some noise in it. Try it and you will understand better. But I didn’t say that you cannot use higher ISO to achieve desired results. I am just share with you the limitation in photography. But still if you are creative, you can use higher ISO to get good results, after all photography is very subjective.

That’s all for the exposure. Hope you benefit from this article and feel free to give any comments or opinions or even tips from you.

Entry Filed under: Beginners Guide to Digital Photography. Tags: Aperture, Exposure, ISO, shutter speed, tips.