We just learned that a DSLR sensor needs an exact amount of light to make an image, and that shutter speed is the only way to increase or decrease the time light hits the camera sensor.

ISO is not used very often but important none the less. Remember how you need to give the sensor the exact amount of light it requires? Well as technology increases so does a sensors ability to pick up light. ISO is a measurement of the sensitivity of your sensor. It is like a dimmer light switch knob in your home. It is very exact and the lower you twist the knob, the darker it is. ISO is also like the volume knob on your car stereo. The higher you turn it, the louder it gets, but noise or static is introduced making it displeasing.

So why would you want the sensor to pick up light faster (high ISO) if it introduces noise into the photo? Well some photographers take advantage of the grainy look for a certain style. But it is barely used for this. It is mainly used so you do not have to take a tripod out with you when you take photos in dark lit environments. I have personally experimented with low lit handheld shots, and I can tell you my hands are not as steady as they once were. All of my photos turn out fuzzy or blurry because the slightest movement during a long exposure shows overlapping light information. (shutter is open for a second of more) Turning up the ISO (or sensitivity of the sensor) allows you to have a faster shutter speed resulting in a sharper night image.

There is practically no reason to turn up the ISO during the day unless you require a certain effect. You will always want a relatively low ISO so your images are not grainy. I personally experimented and took several images with a different ISO and pixel peeped so I know what I am dealing with when I adjust the ISO. Internet images don’t really matter since they are resampled smaller removing most grain, but if you are looking to frame some photos for the wall or print for any reason, I would highly suggest a low ISO.

Please take the time to look at your results from experimenting with the ISO, way too many photographers are afraid to turn up their ISO when they could get crisper images (faster shutter speed) if they did.

In the comments below, please tell me what camera you have and the highest ISO you pixel peeped to be ‘good enough’ for most quality situations.

By the way, if you made it this far, the next post completes the exposure triangle. So you should be able to finally switch to manual mode with confidence like I just recently did.

Next up > Aperture, Why should I care how big the light hole is?