In previous posts, where I covered the first two sides of the photography exposure triangle, I talked about aperture and shutter speed. In this post, I’m going to discuss the third side – ISO. In photography, ISO, in the most basic sense, is the camera’s sensitivity to light. ISO settings can generally range between 24 and 6,400, with today’s cameras climbing all the way up to 25,600 or higher. The lower the number, the less sensitive and the higher the number, the more sensitive.
Having the ability to change your ISO setting on the fly is a super flexible tool that hasn’t always been available. If you remember back to the film days of photography, you surely recall purchasing rolls of film with a number on it. It was most likely either ISO 100 or ISO 200. I can remember seeing some with ISO 400. Nevertheless, back then, I had no idea what those numbers meant. I believe folks “in the know” informed me to just buy the ISO 200 and be done with it. That was a good, all around, general film sensitivity for everyday shooting.
Back then, the problem wasn’t purchasing and photographing with a specific ISO as much as it was that you’d have to use that same sensitivity for the entire roll of film. If you wanted to take outdoor shots in bright light and then indoor shots with low light, something had to give. And with the old point and shoot cameras I used to use, it was generally my photos that would suffer. I’m talking about them being either under exposed or over exposed.
Today, much of that headache has disappeared. And throughout the rest of this post, I’ll show you exactly how you can adjust your ISO setting to truly get the most out of your photos.
Benefits of Adjusting ISO With Digital Photography
One of the primary benefits of utilizing various ISO settings on your DSLR camera is that it has the ability to affect shutter speed. Let me give you an example. Say you’re outdoors on a sort of walking tour around town. You’re shooting everything hand held, which requires a shutter speed of at least 1/60 of a second. Since the sun is out and your environment is relatively bright, obtaining this shutter speed isn’t an issue.
Now let’s say that you happen upon a dark alleyway where you discover interesting graffiti art. You’d love to take some photos of it, but once you meter your camera, you find that the shutter speed is set to only 1/30 of a second because of the lack of light. Your current ISO setting is 200. Since you’ve recently been learning about photography, you instinctively increase your ISO setting by one stop (a doubling), which is 400. Now, when you meter your camera, you see that your shutter speed has halved itself (one stop), and is now 1/60 of a second. With this configuration, you can now safely take the photos you’d like with hand held photography.
So what is ISO anyway? What do those different settings do? Well, the way I learned about ISO was like this – compare it to a home stereo. After light hits the sensor inside of a camera, it gets transferred to the internal workings of the camera, or the processor. It’s then output as a photograph. Similarly, when music is fed into a home stereo, it gets processed and is output as sound.
If you increase the ISO setting on a camera, the sensor amplifies the light that’s let through, reducing the amount of light that’s necessary to produce a photo. If you turn up the volume on a home stereo, you amplify the sound that’s being processed, resulting in louder music.
Have you ever really cranked up your stereo, only to hear very loud music intertwined with a hissing noise? The cause of the hiss at those high levels is impure electronics. Nothing is absolutely clean when it comes to this type of thing, so any audible artifacts between transistors and connections results in dirty sound. The same is true in photography. The more you amplify your camera’s sensitivity to light (increase ISO), the more artifacts you’ll see in your resulting photographs. Due to this, the general rule in photography is to keep ISO as low as possible, but as I mentioned earlier in this post, today’s cameras are pushing the envelope when it comes to higher ISO numbers and cameras are now able to produce great looking photos, even at high ISO levels.
Standard ISO Range
For a while now, the standard ISO range on digital cameras has remained between six settings. I’ll list them here:
If you take a look at the above ISO range, you’ll notice that each one of them is a doubling of the one before. Each doubling, like shutter speed and aperture size, is considered one “stop.” And just like the other two legs of exposure, one stop is equal to either a halving or doubling of light. To clarify a bit, I’ll give some examples, below, of how ISO settings can impact shutter speed.
ISO 100 – 1/2 second
ISO 200 – 1/4 second
ISO 400 – 1/8 second
ISO 800 – 1/16 second
ISO 1600 – 1/32 second
ISO 3200 – 1/64 second
If you set your camera to each one of the above configurations, your resulting photos should all look the same. Each settings couple lets the same amount of light through to the camera’s processor. As you can well imagine, the relationship between ISO and shutter speed opens up a world of possibility for low light shooting as well as action shots.
Now remember, the reciprocal relationship between ISO and shutter speed doesn’t stop there. Adjusting ISO levels is also effective when attempting to maintain a specific depth of field via aperture size. If you’re goal is to keep a deep depth of field, with a fast shutter speed, during a low light scenario, simply increase ISO. Conversely, if you’re goal is to keep a shallow depth of field with a slow shutter speed in a bright situation, by all means, keep your ISO as low as it’ll go.
Many cameras today come equipped with a feature called, “Auto ISO.” This is a handy tool that helps out in many situations. Because your camera will likely have an ISO “sweet spot” or a range of acceptably clean exposure, it’s helpful to introduce limits that keep the automatic nature of this feature in check.
If you set your camera to use “Auto ISO,” your camera should choose the minimum ISO necessary for any given lighting situation. This, in turn, should maintain the best image quality possible. Within this feature, a photographer has the ability to set a ceiling for ISO levels, or a limit that their camera can climb. When the maximum ISO is hit in a low light situation, the camera will choose either a slower shutter speed or a larger aperture. Again, this should help with maintaining the highest quality image.
Discovering Your Camera’s ISO Quality Limit
Every situation where an ISO adjustment may be necessary will be different. Therefore, it’s important to experiment with your camera to find the point at which photographs begin to degrade because of excessive noise. If you remember from above, if you raise your camera’s ISO level too high, noise will creep into your images and perhaps make them unusable.
I recently set my personal Canon T3i up on a table top tripod and took photos of a few items that are set up on a cabinet. I took one picture for each ISO setting on the camera. The T3i’s ISO range lies between 100 and 6400. I then put the images into Photoshop to merge them together as a fairly clear example of how an increase in ISO can affect image quality. I’ll display the image below. To see a larger version, simply click the image.
As you scroll down the image, you should see some quality consistency between the 100, 200 and 400 ISO levels. At ISO 800 and 1600, some noise becomes evident. In the last two shots, ISO 3200 and 6400, noise is clearly visible. For my purposes, primarily using photography for the web, I wouldn’t use an ISO setting higher than 800 when the lighting conditions are near what the lighting conditions were during the time of this experiment. Personally, I would record these results, as well as experiment with other light levels while taking the same types of photos. I would record those results as well, so I have a better idea of my camera’s limits when I’m in the field.
If you enjoyed this post about camera ISO, please be sure to read our articles that cover camera exposure and other photography related topics in our Photography category. Also, to stay on top of our latest posts, sign up for our mailing list, where you’ll receive each and every post we write, delivered straight to your email inbox.