Learning your DSLR: What is ISO?

Did you get a DSLR camera for Christmas and would like to know how to use some of the manual settings? I will write a series of posts over the coming weeks on how you can begin using your manual settings but for now it is just fine to use the auto setting. Cameras are smart and using the auto setting will help you get a great photo. Check out your camera’s user manual to understand how to change your settings.

Let’s begin with ISO. What is ISO?

Finding the right ISO number

ISO in photography is used to measure sensitivity to light. A DSLR camera typically starts at 100 ISO and goes up in the thousands. It is measured in numbers such as 100, 200, 400, 800, 1000, 1250, 1600, 2000, 2500, etc. My camera goes as high as 6400 ISO.

As a beginner, what you need to know is if you’re taking a photo in a brightly lit room, your camera will need a lower ISO number (like 200 perhaps) but if you are in a dimly lit room then you would need to be set at 1600 or possibly higher. If you are using an on camera flash it should be safe to use an ISO setting of around 400.

See the difference in what parts of the photo are in focus from image 1 [ISO 200, Aperture f/2.8, Shutter 1/80sec], image 2 [ISO 800, Aperture f/4.5, Shutter 1/200sec], and 3 [ISO 3200, Aperture f/6.3, Shutter 1/320sec]. The camera adjusted so that the image would have a standard exposure based on the ISO number you choose.
See the difference in what parts of the photo are in focus from image 1 [ISO 200, Aperture f/2.8, Shutter 1/80sec], image 2 [ISO 800, Aperture f/4.5, Shutter 1/200sec], and 3 [ISO 3200, Aperture f/6.3, Shutter 1/320sec]. The camera adjusted so that the image would have a standard exposure based on the ISO number you choose.
Get your camera’s user manual and adjust your camera to the auto setting that allows you to change your ISO only. Your camera will adjust the aperture and shutter speed based on what you are selecting as your ISO in this auto setting.

I recommend playing with the ISO settings, taking a photo of the same image with ISO 200 vs. ISO 800 vs. 1600. You will see a difference in how your camera automatically changes the settings for shutter speed, and aperture. You will also see a difference in the overall image appeal.

See the difference in the noise/grain in the photo from image 1, 2, 3.
See the difference in the noise/grain in the photo from image 1, 2, 3.

Adjusting ISO for a low-light photo

If your ISO is not high enough for a dimly lit room, the shutter will slow down so it can stay open longer to allow more light to go into the camera possibly resulting in blurry images due to motion blur in the image.

The caution I give you is that the higher the ISO number the more likely you will have “noise” in your image especially in shadows. If you need to shoot an image in a dimly lit room, you may want to consider using a flash if the mood of the image you are taking won’t be diminished by a flash.

In the coming weeks we will talk more about your DSLR settings. In the meantime, what questions do you have? Share in the comments!