What is ISO and How It Works

ISO is the third setting that you need to know about in order to get a correct exposure. I’ve already addressed the other two – f-stop and shutter speed in these posts. As I’ve mentioned before the perfect exposure is a combination of these three settings, f-stop, shutter speed and ISO.

ISO stands for International Standards Organization. In a nutshell the setting choices for ISO (50, 100, 200, etc) have been created to represent film speed which rates how sensitive the film is to light. So in days of film if we were shooting a scene outside with bright light then we could use an ISO of 50 or 100. The brighter the light the smaller this number can be. If we were shooting a night scene then we would use film with an ISO of at least 3200. Low light needs film with higher sensitivity to light.

Now, in the digital era our camera’s digital chip (CCD or camera sensor) can be set to emulate the film sensitivity we need. So if we are shooting food in a bright light situation then our ISO should be set to 50, 100, or 200. If we are shooting food in a low light situation and we are not able to use a tripod and have to hand hold the camera then our ISO has to be set to a much higher number because when hand holding you can’t have a shutter speed slower than 1/125th of a second. If you are shooting with very low light without a tripod then you HAVE to set your ISO higher AND open up your f-stop to get as much light into your camera as you can.

Please note:  THE HIGHER YOUR ISO THE MORE DIGITAL NOISE YOU WILL INTRODUCE INTO YOUR PICTURE. In days of film this was called grain. So with that being said the goal is to get the cleanest files you can – meaning the less digital noise the better. I always set my ISO to no more than 100 when I have a tripod and then I set my shutter speed to what it needs to be to get enough light into the camera for the mood I want.

So above this post is an example of the same shot with two different ISO’s. The one on the left is ISO 100. The one on the right is ISO 1600. You can see the digital noise in the darker colors of the crab claw on the ISO 1600 image. It looks like cyan, magenta, and yellow dots. The camera is guessing at what the detail is and creates this snow storm with dots effect.

When we are using images for the web the files are a much smaller file size then when we print. When you shoot with a high ISO your chances of seeing this will be greater when you print these files. So lets say you’re a food blogger and you’re testing a food product and you shot everything at ISO 1600. Now the company you are testing for wants to print some materials. This could cause an issue for them because your ISO was so high you now have digital noise in the darker areas of the image. You’ll be able to get away with this on the web – but a lot of times not when printing and this is extremely difficult to correct later after you’ve shot.

So the above two images are showing how the low resolution images don’t show digital noise as badly as a high resolution image does. Now with this shot there are not a ton of dark areas. If this was a shot that was very dark and moody then you might possibly start seeing the digital noise even at the lower resolution for the web.

A huge factor in how much digital noise your camera might show in the files is the quality of your camera’s digital sensor. It goes to say the cheaper the camera the less quality digital sensor it has. Some point and shoot cameras have been made for low light situations and they would absolutely be using that in their advertising. The higher quality (and price generally speaking) your camera is the better it will be at handling low light situations with a high ISO.

Now for the confusing part – all three settings, f-stop, shutter speed and ISO are closely linked together to get your exposure correct. If you have achieved the proper exposure and then decide you want more shallow dept of field by opening up your f-stop (meaning go to an f-stop like 5.6 instead of f-16 for example) then in order to keep your correct exposure you will have to adjust one of the other two settings accordingly. I will go over this in detail on the post How To Get The Perfect Exposure.

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