Along with aperture and shutter speed, a digital camera’s ISO setting is one of the three variables that you manipulate in order to adjust the amount of light hitting your digital senor.
What is Exposure?
Before you read this article, you may want to take a look at the exposure article first. When you are combining aperture, shutter speed, and ISO, your goal is simply to manipulate these three factors to reach a certain pre-determined exposure setting. By working with these three controls, you can reach your goal exposure in many different way which depend upon the creative demands of your situation. Because each factor — aperture, shutter speed, and ISO all have their advantages and disadvantages, you will want to change these settings based on the needs of your image — but understanding that ultimately you are still trying to work with these three settings in order to get to your desired exposure.
What is the ISO setting on a Digital Camera?
The ISO setting on a digital camera is simply a reflection of the sensitivity of the camera’s sensor. An ISO speed of 200 is a full stop higher than an ISO speed of 100, and is therefore a more sensitive setting for the sensor.
What this means practically is that with higher ISO speeds, your camera will take-in more of the light when you are taking your photograph.
Now you may ask, “well doesn’t aperture and shutter speed also change the amount of light the camera will take-in?” and the answer is “yes”. It’s critical to remember that ISO is just ONE factor in controlling how much light ultimately reaches the sensor, and getting the “right” amount of light is a function of understanding aperture, shutter speed, AND ISO and how they interrelate.
Problems with High ISO Speeds
The greatest problem with high ISO speeds is noise — or possible graininess of your images. When light hits your camera’s sensor, a certain amount of light is processed by the senor. When you increase the ISO setting, the sensor processes more of this light. As you ask the sensor to process more and more of the light (e.g. as you make your ISO settings higher and higher — 800, 1200, 1600, etc), the result is that all of the excess light can get difficult for the camera to process, so there is noise — or an added grainy texture to the digital images.
How to use the Camera’s ISO Setting
Most expert photographers will tell you that when shooting outside, you should use the lowest ISO settings possible (e.g. 100 or 200). They will also tell you that when you are shooting indoors or in lower light, to increase the ISO to allow the camera to get more light (recall the whole point here is that you want to get a certain amount of light into the camera to reach a certain exposure level). When you do adjust ISO, make sure you do it in small (one-stop) increments. So if at ISO 100 you don’t get the exposure you want, then try ISO 200, and then ISO 400. Don’t immediately jump from ISO 100 to ISO 800.
Ultimately ISO is just one of the three factors you need to consider when trying to get a particular amount of light you want to take your picture. Higher ISOs allow the sensor to process more light, but at the risk of more noise added to your images.
ISO is also important when you need a little extra “kick” for an image. If you have framed your shot at a specific aperture and shutter speed, and you just need to get a little more light in there, increasing the ISO can help you get that extra boost to get to the exposure that you want.