Camera ISO Explained

In previous posts where I covered the first two sides of the photography exposure triangle, I discussed 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.

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:

100
200
400
800
1600
3200

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.

Auto ISO​

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.

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.

Here’s a different perspective.

What Does ISO Mean? How Does it Affect my Photos?​

I’m going to keep this section short and sweet. ISO can end up being a huge topic and for a beginner, people tend to talk about a lot of stuff you have no interest in knowing. I’ll keep what I write limited to the basics.

To start off with, I’ll tell you that ISO is an acronym. It stands for the International Organization of Standardization, an organization that has to do with camera sensors and their measurements. It’s an old acronym that’s been carried over since the good ol’ days of film. You don’t need to know any of this. It has no impact on your photography.

What you do need to know is how ISO affects the photos you take. In general, low ISO values on your camera are good. The lower your ISO setting (100-200), the more normal your camera sensor’s sensitivity. The lower the sensitivity, the less noise or grain in the resulting photo. As you increase your ISO value, noise or grain is introduced into your photos as small specks or tiny little dots. You don’t want this. Noise is bad.

Why would you want to go from a normal sensor sensitivity to a higher one? Well, if you’re taking photos in bright daylight, your camera’s normal sensitivity is fine. There’s tons of light to enter through the lens and you don’t need to compensate for anything. It’s only as you enter darker, lower light environments that you may need to crank up the sensitivity. Say you’re in a dark room and your photos are coming out underexposed (dark). If you increase your ISO value, the sensor will become more sensitive to light (like an amplifier), which will, in turn, brighten up the photos. This brightness comes at a price though. That price is grain. So there’s always a trade off. Just remember, the lower the ISO number on your camera, the better.

And even another perspective.

When Should I Change My ISO Setting?​

I’ve always tried to keep my ISO setting as low as possible because I don’t want excessive noise in my photos, but there are times when raising this value is simply unavoidable.

Let me give you a scenario to help illustrate a point. It’s dusk and you’re sitting on a park bench in a city while people watching. You’ve got your camera in hand and you’re ready to take a shot. The perfect and most interesting person walks by and you lift your camera and begin snapping away. You think, “Great job!” But when you review your photos, you see that while the background of each photo is perfectly sharp, in each and every one of them, the person walking by is blurry. “What the heck happened?” you ask yourself. Something has gone terribly wrong.

Well, I’ll tell you what happened. Your shutter speed was too slow. If you had your camera set to shutter priority mode, that’s of your own doing. If you had it set to aperture mode, your aperture wasn’t opened up enough. If you had your ISO locked down to a very low number, your camera may not have had any leeway anywhere other than slowing the shutter speed to create a well exposed shot. Any way you look at it, the slow shutter speed caused the blur and that needs to be corrected.

Your camera’s ISO value is the determining factor when it comes to the sensor’s ability to absorb light. The higher the ISO value, the more sensitive it will be to that light. Conversely, the lower the ISO value, the less sensitive the sensor will be to light. In the illustration above, since you had your ISO number set to a low value, the camera’s sensor wasn’t very sensitive to light at all. To make up for this, it could do two things; either open up the aperture as much as it could go to let as much light in as possible or slow down the shutter speed to allow more time for the light to reach the sensor. If you’ve got a lens that doesn’t offer a large maximum aperture, the only other place for the camera to look is the shutter speed.

Many people look toward lenses with large apertures for their night time photography. This is a very smart thing to do because those large apertures can let a lot of light in to the camera’s sensor. The thing is, sometimes those openings, while large, don’t allow enough light to come in. If you’re working with still life, then sure, feel free to open up those apertures and lengthen the shutter speeds. Since nothing is moving, the shutter speed duration doesn’t really matter. The problems arise when there’s action in your low-light scenes. When people or things are moving and you’d like them to be captured still and sharp, sometimes the largest aperture can’t give enough compensation to correctly capture the scene. At times like these, you’ll need to look toward your ISO setting. If you allow this setting to float automatically, your camera will choose the proper one, so you can feel free to open up the aperture as much as you’d like and then set that quick shutter speed so each and every photo you take is crystal clear and sharp.

At this point, you probably have two questions. First, how do you change the ISO setting and second, what’s a good ISO value to use at night for action shots? I’ll tackle the “how to” question first. On my Canon DSRL, there’s an ISO button right on top. I can push that button and then use the dial to roll back and forth between the different ISO values. When I’m finished with that, I can push the ISO button again to accept the setting change. As for the second question, if you’re shooting your low light shots in shutter priority mode (which you should be), I would leave the ISO value set to Auto. Let the camera choose what to use to properly expose the photo. It’ll do so depending on how dark your scene is. If you’re finding that the ISO number is shooting way up to something like 6400 or higher, it may be time to start looking at lenses that offer larger apertures, such as f/1.8 or f/2.8. Many kit lenses have starting aperture sizes between f/3.5 and f/5.6. These are oftentimes just too small and they don’t let the necessary light through.

For low light shooting, I like to use my Canon 50mm f/1.8. The aperture is huge and I can set my shutter speed to whatever I want and have confidence that my ISO won’t go up too much. I actually have it set to a maximum of 1600 because I don’t want any more noise than I absolutely have to accept. Even 1600 is too high for my taste, but if that’s what I have to do then that’s what I have to do.

Another question may be, are there other times when it may be necessary to increase my ISO value? The answer to that is definitely yes. If you’re engaging in handheld photography and you’re taking photos of movement in lower light situations, you’ll likely want to crank up the ISO. Also, if you’re indoors and there’s lower light, you may need to look at your ISO value, depending on what’s happening in your scene. If there’s a lot of movement and action, raise the value or let it float so the camera can choose something appropriate. If there’s no action, keep the value low and then slow down your shutter speed.

Your primary concern when experimenting with different ISO values is noise in your images. You’ll need to experiment with the various settings and determine your ceiling, meaning, the highest value you’d accept before telling yourself that there’s simply too much noise in your images and that you don’t want to take those anymore. Years ago, I said that my ceiling was ISO 800, but I’ve increased that to ISO 1600 because the quality of camera has gotten better.

I’ve seen scales out there that have been created by various photographers. They say that, in general, you should use ISO 100 in the morning and afternoon when there’s lots of available light in the sky and then raise it to 640 to 1600 and all the way to 6400 as there’s less and less light available. I like this kind of advice, but it’s really overly simplistic. Your scene and your intentions are what should dictate your ISO value as well as the rest of the camera’s values.

Here’s a question; how do you manage your ISO settings? Do you work backwards and set your ISO first and then allow that to dictate your shutter speed or do you set your shutter speed and keep the ISO set to Auto so your camera can make that decision? I’d love to know. I also want to know your feelings on ISO in general. What do you think about higher values? Lower values? What are your preferences? Thanks!