As a special feature for readers, I’m periodically sharing a tip that will help you improve your personal images. Feel free to leave a comment with a future topic you would like to see discussed!

With all other things equal, ISO affects the brightness of the image. Here I chose a shallow depth of field at f/2.8 and a shutter speed of 1/100 to freeze this 4 year old in his tracks. The appropriate ISO for this window lit image would be 800.

The Basics: What is ISO?

There are three main components when exposing an image: aperture, shutter speed, and ISO. Technically speaking, ISO is the “sensitivity of your image sensor to light”. Whats that mean to you? Well, it controls how bright your photos are.

• Aperture controls your depth of field
• Shutter Speed controls your ability to stop or blur motion
• ISO controls the overall brightness in your image

For a simple explanation of how these three pieces work together, read about the Photographic Triangle here.

In film photography days, you would typically see ISO’s range from 100-800. With digital these days, my newest camera, the 5d Mark III, allows me to use an ISO of 25,600 and higher! (If you ask my techie husband, he will tell you that its really not a difference in the sensor, but the processor of your camera. As technology advances, the chip inside your camera can process more detail, thus increasing the ISO range.)

I’m going to avoid getting too technical here as there are plenty of resources online if thats what you want to know about. I’m going to focus on the practical things you can use when you are shooting, like when and why to change this number on your camera.

ISO is not equal from camera to camera, as illustrated above. Both images were made at ISO 400, but you can see the PowerShot G10 is much noisier at ISO 400 than the 5D Mark III.

When to Change ISO?

Before I can tell you when to change your ISO, you must understand the other two parts of the triangle. Aperture, shutter speed, and ISO all control the light going into your camera in different ways. If possibile, before changing your ISO, try to change your shutter speed or aperture. By opening your aperture as wide as it goes (the lowest number, IE. 2.8) you are letting in more light. (Be careful, as this also decreases your depth of field.) You can also slow down your shutter speed to let in more light. (Be careful if you are hand holding your camera. Don’t go below 1/125 unless you have steady hands or use a tripod!)

The basic rule is very simple: always use the lowest number you can. ISO 100 will give you the best clarity and saturation with the least amount of noise. If you are outside on a bright sunny day, you have no excuses- use ISO 100! There, that was easy. Ok, you want to go in the shade, inside, or to a concert? Lets keep talking…

So your aperture and shutter speed are where you want them, but your image is dark. Time to bump up that ISO! How high you go depends on how dark it is. For outdoor images not in full sun, try ISO 400. If you are going inside, try ISO 800. If you are like me, and shooting in a dark reception hall with no light, you may have to use ISO 4000.

Each time you increase your ISO, know that you are increasing the noise/grain in the image. And thats okay! Well, sometimes. ISO 400 from camera to camera may yield different levels of noise. My recommendation is to test your camera and see where the noise starts to bother you. I know that on my Canon 5D Mark III, I don’t mind the noise up to ISO 3200. At that point, I can keep going, but I will then have to reduce the noise in post processing.

There is a constant battle as a photographer: technical perfection vs. “the moment”. Sometimes the moment comes and your camera is set incorrectly. TAKE THE PHOTO ANYWAY! Its amazing what Photoshop can do, really. Obviously the preference is to anticipate the moment, properly expose it for the best quality, and capture the moment. When you are able to do that, go pro. When thats not possible, its technology to the rescue.

Methods to Reduce Noise

So you had no choice but to use ISO 1600, and now your image is grainy. It happens! When there is no in-camera solution to your problem, there is software such as Adobe Lightroom, Adobe Photoshop and NIK Dfine to the rescue.

Personally, I use Lightroom. Its so incredibly simple and fast to reduce noise. Its as easy as adjusting a slider.

In Lightroom, open the 'detail' panel and move the Luminance slider to adjust the noise levels. Usually 20-50 is enough, and using full strength at 100 can make your images look painterly or fake.

In Photoshop, there is a filter which does much of the same thing. From the drop down menu, Filter -> Noise -> Reduce Noise. Adjust the “Strength” as needed until you have your desired look.

I have heard wonderful things about NIK Dfine, but cannot say I have used it. If Lightroom or Photoshop is not giving you the desired results, I would check out this plugin. This would be if you have a particularly complex image you would like to make specific local adjustments to.

There are many other pieces of software out there. Do you use something else? If so, share your experience in the comments.

Further Reading

Looking for a quick reference to help improve your photography? Living in the Stills has created this useful and colorful Manual Photography Cheat Sheet. Its a great resource, for zero dollars. Check it out!

For ISO explained in terms of worker bees, see this photo.net article.

A beginners guide to ISO. Some good examples in easy to digest language.

Next up

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Was this helpful? Please let me know! My goal is to help you take better photographs when you don’t have a professional around! Of course, when you need a professional, I hope you will call me! Thanks for reading!

Special thanks to my nephew Joey for helping me to illustrate this blog post. You were a most excellent model!