Learning ISO

In my previous post, I talked about Darcy's genius analogy comparing shutter speed to a running faucet.  Leave the faucet running too long, the cup overflows - your image is overexposed. Not long enough, the cup doesn't fill - you're underexposed.

If shutter speed relates to how long you have the water running, ISO controls the flow of water.

ISO is the level of sensitivity your camera is to light.  The lower the ISO number, the less sensitive it is to light, while a higher ISO number increases its sensitivity. The piece within your camera that controls and changes the sensitivity is the "image sensor." It's the most important component of your camera that  gathers light and transforms it into an image. With increased ISO, your camera is able to capture images in low light situations. It comes at a cost however, because high sensitivity can add grain or noise to your image.

My camera comes with a "base ISO" of 100, while most Nikon's start at 200. When there is plenty of light, it is best to stick with the lowest ISO in order to retain the most detail and have the highest image quality. However, it's not always possible when you are capturing images in low-light conditions. Anytime you want to shoot indoors without a flash, set your ISO to a higher number to be able to freeze motion. Other cases you might need higher ISO is to capture ultra-fast shots, like sporting events or flying birds.

Starting at 100, your ISO number doubly increases with every notch… 200, 400, 800, 1600, 3200, etc. So it's important to remember with each step between the numbers doubles the camera's sensitivity to light. For example, ISO 200 is twice as sensitive to ISO 100, while ISO 800 is eight time more sensitive the ISO 100. So, what does it mean when a sensor is 1600 times more sensitive to light? It means that it needs 16 times less time (shutter speed) to capture an image.

ISO Speed Example:
ISO 100 – 1 sec
ISO 200 – 1/2 sec
ISO 400 – 1/4 sec
ISO 800 – 1/8 sec
ISO 1600 – 1/16 sec
ISO 3200 – 1/32 sec


Notice how with every increase of ISO, the shutter speed is halved? This means you can get the same mathematical exposure if you adjust the ISO and shutter speed in doubles and halves. For example, if you captured an image at ISO 100 at 1 second, by simply switching to ISO 800, you can capture the same image at 1/8th of a second. This could mean the world of difference in your photography because it can freeze motion and make for a very crisp photo!

Here is what I shot while messing around with ISO today: 

ISO 3200 f/5.6 1/125 

ISO 200 f/2.2 1/80