Good morning!! Today is the third post about creating your exposure triangle. This is the easiest one to learn! ISO (eye-es-oh) is the level of sensitivity of your camera to available light. The lower your ISO number is the less sensitive to light your camera sensor is. The higher your ISO number the more sensitive your camera sensor is. Most dSLR's have a base ISO of 100. The max ISO varies greatly between cameras though.
When do you raise or lower your ISO? If I'm shooting on a bright sunny day, my ISO will most likely be set to 100. If I'm in heavy shade, it's an overcast day, the sun is setting or I'm indoors, then I will raise my ISO accordingly. How much do I raise my ISO? It depends on how much I need to! However, something to keep in mind is that the higher you boost your ISO, the more grain will be in your image. Most beginner cameras will start showing noticeable grain around 400 ISO and will be a nuisance around 800 ISO. This is also very typical of crop sensors. If you are shooting with a full frame camera, you have more leeway to boost your ISO to an astronomical number! I shoot with a Canon 6D body (which is a full frame sensor) and have the ability to raise my ISO to 8000. I've shot at 8000 before and yes there was some grain, but nothing I couldn't fix in post production.
Below are three examples of choosing ISO. I'm about to go all Three Little Bears on you!
The ISO in the first image is too low, the second is too high and the third is just right! It was during sunset with no direct light since it was blocked by a house. Note that all images are SOOC (straight out of camera).
I hope this was helpful! Please let me know if there are any questions. Next week I will be doing one last post about the exposure triangle. That post will tie everything we've talked about over the last three weeks into one post and teach you how to know when to change each setting!