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ISO
and
sensitivity

Today is the first of Stef's lessons for you for this course, and he's here to talk to you about some of the technical aspects of making correctly-exposed images. Over the next three lessons he'll take you through three easy-to-undertand exercises that will help you photograph your creations correctly. First up – ISO.

Understanding ISO and sensitivity

In film photography ISO measured the sensitivity of the film to light. The lower the number (eg 100 ISO) the less sensitive the film and the finer the grain on the images produced on that film.

In digital photography the same ISO numbers are used and the sensitivity the numbers measure is the sensitivity of the image sensor. The higher the number the more sensitive your camera is to the light and the more grain will appear on your images.

On lots of your cameras you will have the option to use Auto-ISO. I was so excited when Auto-ISO came along because it meant that for most of the time I didn't need to think about the ISO and I could get on with concentrating on composition, light, focus points etc. However, because I already had a knowledge of choosing the right ISO, when my camera wasn't doing what I wanted it to and I wanted to override the Auto-ISO then I knew what I wanted/needed to do.

So, instead of just telling you to pop your camera on Auto-ISO and never worry about it, I want you to regularly spend time taking it off Auto and choosing the ISO you need for the circumstances you are shooting in.

You can also pay attention to the ISO that your camera is choosing for you when you are shooting in Auto-ISO mode.

Here is a list of good starting points for you.

  • ISO 100 outside, bright day
  • ISO 200 outside cloudy/dull day
  • ISO 800+ indoors
  • ISO 1600+ low light

Generally, you always want to use the lowest ISO you can to avoid grainy/noisy images. Unless of course you want to create that grainy look of film in your image.

However, higher ISOs allow you to shoot in low light without having to use a flash.

If you have taken your lens down to the lowest aperture it will go but your shutter speed is still too slow and your images are all blurry, then the next thing you can adjust is the ISO.

One thing to be careful of is if you have been taking images indoors at a high ISO and then go outside and forget to reduce the ISO down to a lower number you might find your images are overexposed or even sometimes just all white. Don't panic, just reduce the ISO back down. This used to always be a nightmare when I worked as a wedding photographer and I'd leave a dark church and then open the big doors to a bright Summer's day, usually walking backwards as the bride & groom walked down the aisle and out of the door. I'd be caught up in the emotions of the moment and focussing on capturing those and the composition. The last thing I wanted to worry about was turning down the ISO...which is one of the main reasons that I fell in love with Auto-ISO when I first had it on my camera!

Have a go at experimenting with the ISO, especially when you are indoors.

Emily xo

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