Aperture, Shutter Speed and ISO for dSLR and Point&Shoot Cameras

Bright day, Shutter speed 1/1600, f/7.1, ISO 400, 180mm

Aperture, shutter speed and ISO, (aka the exposure triangle) is one of the most important photography concepts to learn. Don’t let these terms throw you. We’ve discussed Aperture and depth of field, Aperture part 2, Aperture Made Easy and Shutter Speed. Today we’ll discuss a bit more on aperture and shutter speed, and learn about ISO.  

Depth of Field Chart:

The exposure triangle is a simple concept to learn and it allows you much more control over your photos. Again, the exposure triangle is a combination of aperture (f/stop), shutter speed and ISO.

Exposure is simply the amount of light that reaches your camera’s sensor. We need to catch just the right amount of light to show off all the details of our image. Too much light gives us an overexposed photo; too little light gives us an underexposed photo.

How do we control exposure? By using a combination of aperture (f/stop), shutter speed and ISO.

Shutter speed:

As we learned in the post on Shutter Speed this is a measure of how long the camera’s shutter is open. A fast shutter speed might be around 1/1000th or even 1/2000th of a second, while a slow shutter speed can be up to several seconds or longer, plus a series of speeds in between. The longer the shutter is open, the slower the shutter speed, and the more light we capture.

*These are rough figures. These rules typically don't apply with cameras that have built-in anti-shake or vibration isolation mount lenses. These lenses work against the movement of the camera when you hold it in your hands.

The shutter speed settings you use depend on the situation and the effect you want to achieve. If you are photographing a fast-moving object like a race car, then you’ll need a fast shutter speed to prevent blurring unless blurring is your intent. For no blurring you’ll need a wide aperture to let in enough light in the short space of time the shutter is open.

Good shutter speed, f/stop and ISO:

Photo credit, Sherri Maxwell

Camera settings too dark:

Photo Credit Sherri Maxwell

If you want a deep depth of field, you’ll need to use a narrow aperture, and a slower shutter speed.

A key to finding the best shutter speed and aperture combination for your image is to experiment with several different combinations. Each setting will give your scene a unique ‘feel’. You’ll be surprised that often a counterintuitive setting will produce a great photo.

Shutter Speed 500

What is ISO?

ISO

The other factor beyond shutter speeds and apertures that will affect the overall exposure is ISO which is a measure of the sensitivity of the images sensor.

ISO sensitivity is a measure of how fast the image sensor reacts to light. A higher sensitivity means that the camera needs less light to make an exposure. This allows an exposure to be made with either a faster shutter speed or a smaller aperture (f/stop). See-our exposure triangle at work. The specific ISO setting you choose determines this sensitivity. If you’ve shot film before, then you are already familiar with ISO ratings of film, such as 100, 200, or 400.

With a digital camera, the higher you set the ISO, the less light your camera will need. When using a higher ISO the more likely you will be able to hand-hold a shot in lower light without the camera shake that will give a blurred image. If you are using a lower ISO, you will need much greater light levels, or a tripod, to ensure a steady, sharp shot.

In digital photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor concert or sport event when you want to freeze the action in lower light) – however the cost is grainy, or noisy, shots.

Low ISO will leave you with shots that are smooth and sharp for the lighting conditions that you’re in. This may be the recommended application in most situations but there are times when pushing your ISO setting to its maximum can create some interesting effects.

Grainy or noisy shots can give your image a gritty and raw quality that creates a completely different mood in your shots. I especially like high grain and a raw look in street photography.

If you would like a print-out of these charts email me at mariwilbur@gmail.com. Please put "photo charts" in your subject line. 

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Next blog - something light and easy - I promise. 

Happy clicking.