The Exposure Triangle - what is it and why do you need to know? (Cheshire photography course with Picture It Big)

Click on the image to see a larger version

If you've started to wander off the AUTO setting on your camera and are having a play with the Aperture (Av / A) or Shutter (Tv or S) setting, you'll have noticed that when you alter one, the other changes at the same time. This is because they work together to make sure that your picture will be correctly exposed.

Just in case I've already used a bit of jargon that's confusing, let's cover that off first.

The obvious question you might be asking at this point is why would you change the aperture or the shutter speed, rather than let the camera do it all for you on AUTO? Well it puts you in control of the type of image that you take, rather than pointing and shooting, you are determining the outcome and can get creative. Probably the whole reason you splashed out and bought a bridge or SLR camera rather than sticking with a compact. (Some compact cameras do allow you to set the aperture and shutter speed and all this applies to those too!)

So, first of all, why would you want to change the aperture? Have you ever wondered how you get that amazing soft focus, blurred areas in a photograph, whilst the point of focus is still completely sharp, like in the picture of the baby? Aperture, that's how! Set a low aperture like f/2.8 (which crazily is a big opening in the lens) and you'll get a lovely soft background. This makes your subject stand out nice and crisp and opens up a whole world of creativity. This is also called a narrow or shallow Depth of Field.

If you set a high aperture number like f/16+ then your image will be in focus from front to back. Typically you might do this with landscapes. And whilst you're in control of the aperture, your camera is setting the right shutter speed to get the exposure right.

So, what about shutter speed? This is how long the opening in the lens is open for and it can be anything from the tiniest fraction of a second through to several seconds. If you select a fast shutter speed any movement is frozen - anything higher than 1/500th of a second is considered quite fast. Slow shutter speeds blur movement and can be used to great creative effect. If you use a slow shutter speed - anything less than 1/60th of a second, you need to rest the camera on a flat surface or use a tripod to avoid camera shake.

I started off this blog by saying that aperture and shutter speed work together to get the right exposure. In order for a picture to be correctly exposed the opening in the lens needs to let in enough light onto the camera sensor. If you have selected a small opening, then it needs to stay open longer than if you selected a large opening - simple isn't it?!

But sometimes there simply isn't enough available light to do what you want to do. A situation I've faced a number of times is photographing a child running along a forest path, where the overhead canopy of leaves has reduced the amount of light. The camera is on its lowest aperture setting (biggest opening in the lens), but the shutter speed is still too slow to freeze the child's movement. I don't want to use the flash as it's so flattening and it wouldn't reach the child anyway. But there's another option available to me, thank goodness - the third part of the Exposure Triangle, the ISO setting.

ISO determines how sensitive to light the camera's sensor is. In the olden days of film (!) you could buy reels of film that were more or less sensitive to light and your digital camera's ISO setting is the equivalent of this. The higher the ISO number, the more sensitive to light. So in nice bright conditions you use a low ISO number - 80-200 and in duller conditions you could use a higher one like 800+.

When you use a high ISO number you will find that your shutter speed increases - yay! The only downside to high ISO numbers is that you can get a grainy effect in your images. It depends on your camera how pronounced this is. Top end cameras handle high ISOs well, whereas compact cameras can be notoriously bad. If you leave the ISO set on AUTO the camera will decide what to do for you. Call me a control freak but I prefer to know what it's doing!

So there you have the three settings that make sure your pictures are correctly exposed:

Aperture
Shutter Speed
ISO

And I've even created a handy Exposure Triangle diagram to help you remember it all!

Click on the image to see a larger version

I can bring all this to life for you in a bespoke one to one photography class, tailored to your requirements. To find out more or to book click here.

By Jane Burkinshaw. Share this post by clicking on one of the Share buttons on the right hand side. I'd love to hear your comments too!