A Bit Beyond the Basics Part I: ISO, Shutter Speed, and Aperture

Photography would be so much simpler if the camera worked like the human eye. But it doesn’t. Therefore, it is vital to understand what a camera will and will not do. In order to create an image that represents your vision, you must develop an understanding of how the camera functions and how to use those functions to reach the desired end result.  Beyond the camera there is post-processing software, such as Lightroom and Photoshop, that can help further develop the vision.

Whether you have a Canon or Nikon point-and-shoot or DSLR your camera most likely has a Mode Dial on the top.  If you haven’t changed anything your mode dial is probably on P (Canon, Sony, Fuji) or Auto (Nikon). In this mode the camera uses its internal light meter to determine the ISO, shutter speed, and aperture values to use.  You just focus and take a picture.  This works well for most snapshots, but not so well if you are trying to achieve a particular effect.  ISO, shutter speed, and aperture are part of the exposure triangle and adjustments to these three values are what allow you capture an image as intended.

Canon Mode Dial                            Nikon Mode Dial

All three elements of the exposure triangle interact with each other. Changing one usually requires a change to another. For right now, we are going to try to look at them in isolation by using some semi-auto modes on your camera and watching how the camera adjusts.  In part two we will begin to look at each element of the exposure triangle in more depth.


I did not know what the letters in ISO represented but thought I should find out before I wrote this post.  They stand for International Standards Organization. I wasn’t missing anything because what the letters stand for is completely unhelpful to understanding how ISO matters in photography.  Back when we used film, the ISO number indicated the film’s sensitivity to light. I used to shoot with ISO 64 slide film when capturing landscapes. Most people typically chose ISO 100 film when shooting outdoors and ISO 400 or 800 for shooting indoors.  The higher the ISO number the higher the film’s sensitivity to light.  So why not shoot with ISO 400 or 800 all of the time? As the ISO increases so does the grain (film) or noise (digital).  When there is sufficient light one can achieve a higher picture quality using a lower ISO because there will be finer detail and less graininess in the photo.  Even though most of us no longer use film, digital cameras have adjustable ISO and function in the same way as a film camera with one HUGE advantage; when you move from outside to inside and want to take a quick photo of your adorable child, you don’t have to change film.  You simply press the ISO button on your camera and change the number.

ISO can function more independently than the other two elements of the exposure triangle and it deals primarily with light. If you need more light-gathering capability and you can’t achieve the results you need by adjusting other settings, then you will need to raise the ISO.  If you haven’t changed anything, your camera is probably set to Auto ISO.  In order to really learn from the semi-auto modes we are looking at today, you will want to change your ISO to 100.  The method for changing the ISO varies by camera and many even have an ISO button.


Shutter speed is exactly what it sounds like.  It is the speed at which the shutter opens and closes to take a photo.  When the shutter is open it allows light to pass through the lens and hit the camera’s sensor.  The sensor in a digital camera is essentially the film.  The amount of light hitting the sensor helps determine the brightness of your photo.  Common shutter speeds can range from 30 seconds for photographing stars to 1/2000th of a second for freezing fast action.  The proper shutter speed for any photo is determined by the ISO, aperture, the amount of ambient light, and what you are trying to achieve with your photo.  If the shutter is left open too long the picture will be over-exposed and too bright. A shutter speed that is too short will result in a photo that is too dark.  The extremes on either end make for an unusable photo.  Any parts of your photo that are completely white or completely black will have no detail.

The length of time the shutter is open also affects whether the subject is blurry or clear.  If you have ever tried to photograph children indoors you probably have several photos with a colorful streak that is supposed to be a child.  To compensate for the low light indoors the shutter will stay open longer to let in more light. The children move faster that the speed of the shutter resulting in blurry photos. Once again, it is necessary to adjust other elements of the exposure triangle to compensate for this.  It is also important to remember that none of us can hold a camera completely still for very long.  Longer shutter speeds usually require the camera to be on a tripod.

APERTURE (or f-stop)

For me, aperture is the most versatile and most important element.  Simply stated, aperture is a number indicating how much light the lens is letting in through an adjustable, circular opening.  An aperture number, such as f/22, means that the opening is really small and only a small amount of light is being let in.  A smaller number, such as f/1.4, means that the aperture is wide open and letting in a lot of light. I know, it seems backward.  So a bigger number means less light and a smaller number means more light. Along with ISO and shutter speed, aperture deals with light and how much of it reaches the sensor.  Additionally, aperture is the setting responsible for how much of your photo is in focus.  If you have ever seen one of those beautiful portraits where the main subject is in perfect focus and the background is beautifully blurry, then you are seeing the results of using an aperture such as f/1.4. When you look at an expansive scene with a lake, trees, and towering mountains in the background and everything is sharp and in focus you are seeing the results of an aperture around f16. Of course, there is a lot more to all of this and we will take an in-depth look at each of the three settings in future posts.


Notice that at f/1.4 the aperture is almost completely open, letting in a lot of light                                                while at f/16 the aperture only allows a small amount of light to enter the camera.


If you are at all like me, then I’m sorry. Really though,  if you are at all like me then you learn best by doing so here is what you are going to do with these little tidbits of information.

First, set you ISO to 100 rather than letting the camera decide.  You are going to want to see how the camera adjusts itself to different shooting situations and this is easiest to do if you remove one of the variables.

Look at the Mode Dial on your camera. If you have a Canon, you will see Av,Tv,M, P, and a few other letters or pictures depending on the camera model.  On a Nikon, Sony, and most Fuji cameras you will see A,S,M,P and other various pictures and letters.  If you have another brand the letters are probably similar.  We are going to start with the Tv or S (Tv stands for Time value and S is for Shutter priority). This setting allows you to set the shutter speed and the camera will adjust the aperture to the proper f-stop.  Try adjusting the shutter speed and see what happens to the aperture.  As you increase the shutter speed, the aperture number will decrease meaning the opening will be wider to let in more light to compensate for the fact that the shutter will not be open as long.

Shutter speeds: This number will show up in the viewfinder or on the LCD screen. When your camera reads 100 for the shutter speed, it really means 1/100th of a second.  Most of the numbers represent a fraction of a second. When you reach numbers that read 1” or 3” this means 1 second or 3 seconds.  Once you move beyond 30” you will need to use Bulb mode and that is a subject for another article.

Now change the Mode dial to Av or A (Av stands for Aperture value and A is for Aperture priority).   Adjust the aperture and watch how your camera adjusts the shutter speed to compensate.  There are charts that show you all of this, but I think it is easier, and makes more sense, to learn while actually using your camera.  Try taking photos indoors and out to see how your camera adjusts.

Aperture: When you look through the viewfinder or look at the LCD screen, the aperture value will be a decimal number. Depending on the lens and/or camera, some common values are 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, and 22.0. Your camera may have numbers between these.  Remember that the smaller the number, that larger the opening and the more light coming in.

If you want to see what happens when you let your camera choose the ISO, change the ISO setting back to Auto and continue to play with the Aperture Priority and Shutter Priority settings.  Remember that, depending on your camera, ISO values above 400 begin to show digital noise (graininess) in the photo.  This is why I leave my ISO on 100 for most photos and adjust the other two variables to compensate for low light.

Next week we will look more closely on how ISO, Shutter Speed, and Aperture interact to help you create a photo that represents your vision.


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