iso

The exposure triangle : A brief lesson on exposure

Hi all,

I thought today would be a good day to write about the exposure triangle and how it works.

For those of you who are new to photography this is a crucial piece of information that you must take with you. I wont be getting too technical but I will be explaining how the exposure triangle of shutter speed, iso, and aperture work together and how they may affect one another.

So let’s get down to the basics and I shall explain what each one is and its function.

Shutter speed

The shutter speed essentially determines how much light hits the sensor while passing through the shutter once the release has been pressed. The faster the shutter speed the more motion it will freeze whilst letting less light into the sensor. Just say for instance if someone is running and you have a fast shutter speed of 1000th of a second, it will freeze that person in motion. However if you have a slower shutter speed lets say of about 1/4 of a second then it will blur moving objects and give a sense of movement throughout the image.

Just remember this does not only apply to people, but shutter speed can affect any moving bodies such as water, clouds, crowds and anything else that moves. It all depends on what story you are trying to tell in your photograph.

Aperture

Aperture is when the blades form a circle within the lens when the shutter release is pressed. This determines how much light will hit the sensor whilst passing through the aperture blades.

Things to remember:

The higher the aperture number the smaller the physical hole. The lower the number the larger the hole the blades form.

The larger the aperture the less in focus your image will be, and the smaller the aperture the more in focus your image will be. But I personally wouldn't go over f16 (Also the larger the aperture the more light, the smaller the aperture the less the light that will go through to your sensor)

The function of aperture can also determine how much of the image will be in focus depending on the cameras focal point whilst increasing or reducing the amount of light hitting the sensor. For example if I had an aperture of f2.8 and chose a building in the background to be my focal point then that building would be in focus and the foreground and part of the middle ground would be out of focus. On the other hand if I had an aperture of f8 or higher while keeping the same focal point then the foreground and middle ground of the image would be more in focus than that of the image taken at f2.8. Again this is only a brief idea to get you started, but just keep in mind whilst photographing at higher apertures up to f8 then its usually better to photograph with a tripod to avoid camera shake. (These examples have not included hyperfocal distance as I will be talking about that in my next post)

Iso

Iso is tool within a camera to determine how sensitive your camera sensor is to light. The lower the iso number the less sensitive to light your camera will be, therefore the image will have less grain (noise) and more detail. The higher the iso number means your camera sensor will be more sensitive to light and will result in more grain (noise) and wont give you as much detail.

An example of this would be photographing an event indoor where you may not have adequate lighting and may need to boost the iso to 500-1000. When opening those shots on the computer you may notice a certain amount of grain on your image and although it wont necessarily destroy your image, iso does lower the quality and depending on the size of your sensor.

That does not mean you should be shy to use iso. I have photographed many a beautiful image that has used around iso 3200 (full frame) and have still come out with very usable shots. Also about sensor size the general rule is: The larger the sensor the more quality and less grain you will encounter whilst using high iso. That being said the difference is not always apparent if you aren’t going to pixel peep.

How it all works together

Upon reading the above you may start to have an idea on how it may all come together seamlessly, so if you were right in fitting the pieces of the exposure puzzle together let me give another brief explanation and another example.

When the three elements of shutter speed, iso and aperture are brought together then you get the exposure triangle. Each of these elements works seamlessly together when trying to create a perfectly exposed image.

Each in a harmonious balance the three parts of the exposure triangle work together seamlessly.

The best way I can give you an example is if I tell a story…So, it’s a dark night in the city, but you happen to be by the waterfront and you see the vast beautiful array of buildings around you. You realise that you have your camera and tripod with you, so you decide to take a shot. As you set up your camera you realise that it’s dark outside but the city lights are helping to illuminate the scene whilst causing beautiful reflections in the water. You stand there for a moment and think how to take this shot?

Here are your points for consideration

  • Shutter speed (fast or slow)

  • Aperture (How much of it do you want in focus)

  • ISO (Will a high iso ruin the shot by adding too much grain?)

  • Tripod or handheld?

OK, since it is night time and you have a tripod on hand you’re likely going to use a slow shutter speed because not only will it allow enough light into your camera but it will also smooth out the water giving it a silky smooth look (if that is what you want). Next on our list is aperture. You would likely use a Small aperture of about f8 because this will keep the whole cityscape in focus, especially since the buildings are far away from you (focus to infinity). Next and last on our list is Iso. Again you would use a fairly high iso of around 6400 or more. This can all change dependant on what you are trying to do, but if it’s a generic cityscape then this should be ideal. However if you decide you want the water in the scene to be frozen to keep the details in the ripples then a faster shutter speed would be needed which would increase the Iso adding more grain to your image. The aperture can be left the same because if your aim is to get everything in focus then the f8 setting would be sufficient.

Now we have delt with a simplified explanation of the exposure triangle at night, lets have a look at it during the day.

The obvious thing is when more light is availabe then the shutter speed does not have to be low and the iso does not have to cranked so high. You can even suffice with iso 100 (the lowest setting on most cameras). However the aperture is different, the reason for this is focus and the how much of the image you want to be sharp. For a hand held image if it’s a bright day I am happy using an aperture of 5.6, because it keeps the image in focus.

However, we all know even on a lovely summers day light can change. So consider this, you have set up your composition and you don’t have a tripod, but you know where to stand and you have dialled in the a shutter speed that is adequate enough not to cause camera shake and your aperture is set to f5.6 and the ev meter (the meter that goes minus 5 to the left and plus 5 to the right) is comfortably sitting at 0. Brilliant! you have a correctly exposed image! But when you think everything is going great and just before you press that shutter release button the light drops a notch causing your image to be under exposed…What would be the right thing to do? That’s right you guessed it! Crank up the Iso to compensate for the drop in exposure. If the opposite occurs and the scene has too much light but your iso is at its lowest and apeture is just right then the next thing to to would be to use a faster shutter speed to compensate for the over exposure.

These are just guidelines to go by whilst you are still learning about your camera. There are many concepts and techniques that have not been discussed yet…But rest assured more is to come on this subject. The best thing to do in my opinion is to keep it simple and follow these guidelines until you feel comfortable playing around with exposure. I am currently writing a piece on focus to go hand in hand with this piece, so just keep your eyes peeled for the next post.

I really hope you enjoyed reading my brief lecture on the exposure triangle and I look forward to providing you guys with more on this subject later on.

Until the next time

Kind regards

Adam