ISO IN PHOTOGRAPHY

The definition of ISO (International Standards Organization) is the organization that sets standards for measures such as sensor sensitivity and output. In a nutshell, ISO in photography, is sensor sensitivity. You set the ISO speed to indicate the sensitivity to the emulsion of light. Setting your sensor's sensitivity (or ISO) to a high number will let you shoot in low light. Using a lower ISO will give you maximum image quality, but you may need a tripod to hold the camera steady because you are letting less light into the cameras sensor and it takes longer to expose the image onto the sensor.

To better understand the effect of ISO on exposure, think of ISO as a lightbulb. If your camera is set to ISO 100 you essentially have a light bulb that is low wattage like a 40 watt bulb. When you walk into a room with a 40 watt light bulb it is harder to see than if you had installed a 80 watt light bulb in the same room. If you set your camera to ISO 200 it is like walking into a room with the brighter 80 watt light bulb and it is easier to see. There is more light available to the eye. The same goes for your camera. At ISO 200 more light is amplified to your camera sensor than at ISO 100. 

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How Does Aperture Relate To ISO?

If you had two cameras and both were set at an aperture of F/5.6 this would mean that the same volume of light would be coming through both lenses on each camera. If one camera was set at ISO 100 and the other was set to ISO 200 then the camera set at ISO 200 would amplify more light at the same aperture of F/5.6. It would be like standing in the room with the brighter 80 watt lightbulb and it was easier to see at ISO 200. The camera set at ISO 200 would be able to record the image faster than the camera set at ISO 100. The ISO 100 camera would be like standing in the low light room with a 40 watt bulb. Even though each camera has the same F/5.6 aperture.

Think of it like turning the dimmer switch up and down on the lights. The higher the ISO speed the brighter the light gets when the dimmer switch goes up. The lower the ISO speed the lower the light goes when the dimmer switch goes down. When setting the the speed of your ISO think of your camera sensor as the room with the light and the ISO as the dimmer switch in that room. When you turn the dimmer switch up and down you are amplifying the light up and down on your camera sensor.

How Does Shutter Speed Relate To ISO?

Let's assume that we are walking into a room with low light, like the 40 watt bulb mentioned above. It takes longer for your eyes to adjust to darker room. If you walk into a brighter room, like the 80 watt bulb, your eyes don't need as much time to adjust to the light. Remember we have two cameras, one is set at ISO 100 and the other at ISO 200, both with an aperture of F/5.6. When both cameras shutter speeds are adjusted for the correct exposure the camera set at ISO 100 will take longer to adjust to the light and hence the shutter speed will be slower. The camera set at the higher ISO 200 will be able to adjust to the light quicker and hence will have a faster shutter speed. Again, we turned the dimmer switch up on the light and our eyes adjusted faster at ISO 200 than they did at ISO 100. Your camera sensor is like your eyes adjusting to the light when it relates to ISO in photography. 

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What Is ISO Noise?

A common analogy is that digital ISO noise is like turning up the volume on the radio to hear a faint signal better. The signal itself doesn't change, but turning up the volume means you can hear it more clearly. However, when you crank up the volume on your radio you also introduce other unwanted noises and background hisses. When you increase your ISO in photography from 100 to 1600 you are essentially turning up the radio and the camera sensor is also receiving unwanted background hisses and noises.

When you crank up the ISO in photography you are essentially exacerbating any non-image artifacts that we call "noise." These unwanted artifacts are amplified onto your camera's sensor and you are introducing noise into the image. ISO noise is more apparent when shooting in low light situations. When the light is low and you need to crank up the dimmer switch you are essentially cranking up the volume on your radio to hear the signal better even though you know you are going to get more background hisses. 

Conclusion

What is ISO in photography? ISO in photography is a way to control the amplification of light that hits your cameras sensor. The higher the ISO the greater the sensitivity to light, the lower the ISO the less sensitivity to light. You are essentially turning up the dimmer switch on the lights. If you turn the dimmer switch up too high you are going to get non-image artifacts that will create noise. Using a lower ISO will give you maximum image quality, but you may need a tripod to hold the camera steady because you are letting less light into the cameras sensor and it takes longer to expose the image onto the sensor. 

"Nature is the mother of all art." ~ Robbie George