Photos Matter: Exposure Part 1 | ISO
There are three main camera settings that are responsible for a correct exposure: ISO, aperture, and shutter speed. These three settings are inseparable; if you change one of them, it affects the other two. When you are able to understand and use these settings, you have a lot more control over the resulting images. Today’s blog post is the first in a series of posts that will help us understand these three settings better, and will explore how to put them together to create beautiful images.
The first setting we’ll tackle is ISO. Most cameras allow you to adjust your ISO, including point and shoot cameras. The ISO setting determines how sensitive your camera’s sensor is. The higher your ISO number, the more sensitive your camera is to the light coming through the lens. This is particularly helpful in situations where not a lot of light is available, such as inside your house. Another reason you might need to increase your ISO is if you are using a smaller aperture, which means your lens doesn’t open up as wide when it takes the picture, and therefore is not letting as much light in.
In this example, I was in my living room, using only the light from the window, so I had to bump my ISO up to 800.
So why don’t we just keep our ISO as high as possible all the time? When your camera is more sensitive to light, it is also more sensitive to interference or “noise”. This noise will make your images look grainy.
Here you can see the difference between a low ISO (100) and a very high ISO (3200). It is especially visible in the darker areas of the photo, such as the background and the pupils the cat’s eyes.
At this size, it may be hard to tell, so here are the same photos more closely cropped:
A good rule of thumb for setting your ISO is to keep it as low as possible while still getting a correct exposure. One word of caution, though: don’t keep your ISO low at the expense of your exposure! Underexposing your image and then lightening it up in a photo editing program will create more grain than if you just use a higher ISO in camera.
You can see how much grain is added to this picture when I lightened the underexposed image in photoshop.
Again, a closer crop of each so you can really see the difference:
Try experimenting with your ISO settings this month. Once you get the hang of it, you will see a difference in the quality of your photos and possibly the speed at which your camera takes them. Once you’ve mastered ISO this month, we’ll talk a bit about aperture next month!
Tags: Exposure Series, photography
January 23rd, 2013 at 5:23 pm
Great job on this tut and such wonderful examples
January 23rd, 2013 at 7:56 pm
Li, I feel like I am sitting in your classroom! Your tutorials are so well written and the example really enhance my understanding! I am always checking the calendar to find out when you will be posting!
January 24th, 2013 at 7:20 pm
Thanks for this tutorial. It makes the subject less intimidating. Can I ask though,(at the risk of sounding silly!) but how do you choose the best ISO for your intended photo without going too high. Is there a rule of thumb or is it rather guess work and trial and error?
January 25th, 2013 at 11:20 am
Good question…. you don’t sound silly at all!
In the beginning, it’s mostly trial and error, but as you practice, you’ll get better at predicting what ISO is best. Remember that you can still get a correct exposure, even if you chose a higher ISO than you need, so don’t let it stress you out too much! 
January 25th, 2013 at 3:58 pm
Thanks for that. Will hopefully give it a go. By the way…simply gorgeous, delightful picture of the little girl ?your daughter. That one will be a joy for you to scrap!
February 20th, 2013 at 8:01 am
[...] to master if you want to be able to properly expose your images: ISO, aperture, and shutter speed. Last month we talked a little bit about the ISO setting on your camera. This month, we’ll explore [...]
March 19th, 2013 at 8:00 am
[...] discussing the settings responsible for achieving a correct exposure. So far, we’ve covered ISO and aperture. (Have you been practicing?) The third setting, which we will talk about today, is [...]
April 24th, 2013 at 1:07 pm
[...] trying to achieve a correct exposure for your images, it’s important to be familiar with ISO, aperture, and shutter speed. After that, it’s just a matter of how to put them all [...]