ISO is a term that has migrated over from the old film days. At that time, it was the speed at which the film could record the image. If you used film with a higher ISO number, the sensitivity of that film would enable a faster shot.
Digital Cameras and ISO
In digital terms, we have something similar to what happens with film. The advantage of digital is that you do not have to change the roll of film in your camera. You simply select an ISO number and the camera software makes the changes.
Each photograph you take with your digital camera is a combination of camera settings that adjust the amount of light getting into the camera’s image sensor. If there is lots of light, the photographer has a fairly easy time of getting a good sharp shot. As the light changes, settings on the camera must change as well. The challenge comes when there is not enough light to get a good shot while hand holding your camera.
This is where knowledge of ISO can help. Just as in film, raising the ISO number will cause the image to be recorded faster. Because of this, you can increase your shutter speed or use a smaller aperture if you increase the ISO.
The down side to increasing the ISO is usually that there is additional digital noise. Noise is those little specks that seem to diminish the quality of the picture. They make your picture look like an old newspaper photo.
This picture from reegmo’s photostream on Flickr is a good example of how a picture can be messed up with digital noise.
It has not been that long since the days of ISO 800 would make the picture very grainy. However, in the past several years, improved technology has pushed the quality much higher. You can now buy cameras with ISO numbers as high as 12800 and even higher. Granted, those numbers might produce pictures that are of poor quality, but now the pictures taken at ISO of 800 are much nicer in terms of image quality.
In order to take control of the ISO setting on your camera, you must be shooting in one of the “creative modes.” Those modes are P, Av, Tv, or M (Program, Aperture priority, Shutter speed priority, and Manual). If you choose one of the other modes, such as Landscape or Auto, you have surrendered control of ISO to the camera.
Practical Application Using ISO
It is a great exercise to practice with your camera settings. It is the best way to learn what your camera will do when you change one of the settings.
To practice with ISO, the best conditions are low light. Find a place where the light would normally be a challenge to get an acceptable hand held shot. Set your mode dial on P (Program), and take a picture as you normally would. Using the Info button, take note of the settings the camera chooses.
Next, use the ISO button on your camera and raise it several settings. For instance, if your original settings were ISO 100, raise it to ISO 800. Take the same shot and notice what happens to the Shutter Speed and Aperture. Then push the ISO even higher to see what happens.
The best way to view your shots is on your computer. That is where you can see the effects that digital noise might have as you raise the ISO sensitivity. Zoom in to at least 100% on each of the pictures to check the quality. This will let you know where your threshold for good quality versus poor quality is.
Sometimes, you need to sacrifice a bit of quality for just being able to get a sharp picture. It is worth having a sharp image rather than a blurry one or none at all.
On the new Canon Rebel T4i, there is a setting on the mode dial called “Hand Held night shot”. I tested it recently.
The camera will take 3 or 4 photos in quick succession as you press the shutter button. It then blends the pictures together to make a sharp (maybe) picture.
In my quick experiment, I thought the picture looked pretty good in the LCD preview. However, when I got the picture onto the computer, I was somewhat disappointed with the quality. The T4i had automatically raised the ISO to 12800, and the result is quite a bit of noise.
The good part is that this does let me take pictures in very low light settings without using the flash. Again, a sharp picture, even one with noise, is better than a blurry one or no picture at all.
Have you had any experience with ISO? Try changing your ISO. Then let us know what the results were by leaving a comment.