Exposure Triangle for Beginners: Lesson 3

The exposure triangle for beginners is my attempt to make it easier for you to understand exposure and lay the groundwork for all of your future photography. Understanding exposure is the fundamental building block for your mastery of photography. This will also make it much easier as we progress and learn to shoot in manual mode. Manual mode is where you have full control of your camera and where the real magic happens.

Proper Exposure

Program Knob
Program Knob

Proper exposure ensures preserving details, brightness, and tone in your subject. We’ve all seen underexposed images with dark shadows with loss of detail in those areas. We’ve also seen images that are too bright with no detail in the highlights areas. Exposure is dependent on three things in combinations; Aperture, Shutter Speed and ISO, also known as the Exposure Triangle. Aperture (A-Nikon, AV– Canon), and Shutter Speed (S Nikon or Tv Canon) are on the Program knob while ISO is controlled in your camera menu. Adjusting only one will affect only one part of the exposure triangle. In Manual Mode (M) you have the ability to control all 3 independently.

Definitions for This Topic

  • Aperture is the opening in your lens that allows light into the camera. Similar to the pupil of the eye it can close to let less light in or open up to let more light in. The amount of light through the lens to the camera’s sensor contributes to exposure.
  • Shutter Speed is how long the aperture stays open to receive light. A long shutter speed allows in more light, while a faster shutter speed lets in less light.
  • ISO is the sensitivity of the camera sensor to light. This is very similar to the days of film cameras. For example, shooting ASA 400 film on cloudy days. The lower your ISO number, the less sensitive the sensor is to light. The higher the number, the more sensitive the sensor is to light.

How Does Understanding This Help Me in Photography?

Understanding how exposure is achieved can lead to very creative effects for your photography. Most people start out using their camera in AUTO mode. In AUTO mode the camera is making decisions about your aperture, shutter speed, and ISO. For snapshots, this is usually fine. But suppose you wanted to blur the background, freeze sports action, or shoot inside a low lit building? This is where the creative part comes in. You can utilize each aspect of the exposure triangle to achieve the desired result.

For example, suppose you wanted to photograph a soccer game and you wanted to freeze the action of the players? You might choose the Shutter mode (S). In shutter mode, you select a very fast shutter speed, like 1/1600 of a second. That should freeze the ball in mid-air as well as the players. In this mode, the camera is choosing the Aperture. You could do this in Manual mode as well, selecting the same shutter speed, but choosing your aperture and ISO to be even more creative. In manual with the 1/1600 shutter speed, you can choose a setting to give you more depth of field (how much is in focus) by adjusting the aperture. If it is a low lit arena, you can control how high your ISO goes for better image quality.

Another example would be in portrait photography. On AUTO you may not get the photograph you are looking for. You want the image well exposed and the background blurred, mainly focusing on the facial features of your subject. Aperture or Manual mode would be appropriate. In Aperture (A or AV) mode you select the aperture and the camera chooses the shutter speed. Or, in Manual, you can select the aperture, shutter speed, and ISO.

Not to fear if this seems new. Subsequent lessons will focus on each program mode in more detail.

Exposure Triangle
Exposure Triangle

The Histogram

A histogram is a recording of all the tones in your image as well as the distribution of the intensity of colors. Understanding the histogram can help you see your exposure.

The histogram on a camera LCD screen
The Histogram on a Camera LCD Screen

This visual representation is a way to check your exposure, and perhaps make adjustments. Things we don’t want on our histogram is for all the data peaks clumped to the left or to the right. If it is pushed to the left, the image is dark, underexposed. If pushed all the way to the right, the image is overexposed, too bright. Using your knowledge of the exposure triangle, you can adjust the aperture, shutter speed and/or ISO to brighten or darken your image.

This histogram is what you will see on a typical LCD screen when the histogram is active to view with the image. Your camera manual should help you find this option. In this image, you see the photo of the squirrel, data below and in the top right the histogram. This histogram displays the tone of the image with the darkest parts of the image represented to the extreme left and the brightest parts to the extreme right. Most histograms should ideally spread out across to each extreme but not touching the left or right verticle lines.

RGB Histogram

RGB Histogram
RGB Histogram

The RGB (Red, Green, Blue) histogram looks very similar but will show the intensity of the colors. On most cameras, it can display as RGB all on one histogram while the one above has the red, green and blue channels in their own histogram along with the tone values at the top. I prefer having the channels like this. If you look closely at this histogram you can see the highlights (to the right) were clipped. Again, not what we want. A better option, in this case, would be to adjust our exposure to make it darker, then recheck our histogram.

Under and Over Exposure


A couple of things I should point out in the above illustration. These are examples of underexposed, exposed and overexposed image histograms. Note that on the scale baseline it goes from 0 to 255. This is important to understand. O is pure black, while 255 is pure white. In the middle are all the other tones.

In the underexposed example the histogram is shifted to the point it is heaped up along the left line at 0. This means a good portion of the image is pure black, and there is little to no detail in those areas of your image. Some of this might be recovered in post-processing software like Adobe Lightroom if it were not so much. In the overexposed example, the histogram is pushed and heaped up on the right. That is pure white and will have no recoverable detail. This would not be something that even Lightroom could fix. Any time a histogram is pushed and heaped up on the line to the left or right is called clipping. We do not want to clip.


Blinkies, or highlight warnings, show up on your image if you enable this. Check you with your manual on how to activate the highlight warnings. It’s a good idea to be able to see this, as you will recall clipped highlights record zero data. When activated what you will see on your image in review mode on the LCD is flashing areas over all the clipped, blown out, highlights in your photograph. This can be verified on your histogram as you will see the exposure data shifted to the right touching or heaped up on the line.


So for an assignment, I would like you to check your camera manual and find out how to review your histogram on image review on your LCD screen. Also, look for the setting to activate highlight warnings, “blinkies”. This is something you should set up now and use frequently to check your exposure. Second, get off AUTO and try using the shutter and aperture modes to see how making changes affect your photograph. Your images may not be well exposed yet, but we’re going to cover that in the following lessons. Have fun!

Exposure Triangle for Beginners: Lesson 3
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Welcome! My interest in photography spans 40 years and started with the purchase of my first SLR. Since then my passion has grown to landscapes, beach scenes, and travel photography primarily. Photography techniques I particularly enjoy are long exposures, and what I call splash art. You can see these on my gallery page if it interests you. Currently, I live on Amelia Island in Northeast Florida with my beautiful wife and our wonder dog, Fuji.

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