Photography 101 | ISO
As mentioned in my previous Camera Basics post, ISO is one of the sides to the Exposure Triangle. ISO stands for International Standards Organization, which is a bit arbitrary to how you actually think about it. ISO makes the sensor in your camera more or less sensitive to the available light. It can be 50-100 on the low end and crazy 25,000 and up on the high end. This flexibility is very useful but high ISOs are not without consequence to the quality of your image.
How much available light is there in the environment you are shooting in?
The goal of ISO is to keep it as low as possible to keep the quality of your image as clean and without noise as possible. On a bright sunny day, shooting with an ISO of 50-100 is your best bet. There’s no reason to make the sensor more sensitive to light if there’s already a plethora of light available. Doing so will increase your risk of overexposing your image. Raising your ISO should only be done in a few situations that I’ll cover in a future post.
So, what happens when you’re not in the full sun? Well, you will have less available light and you’ll want to increase it. ISO can be measure in full stops or 1/3 stops depending on how you have it set up in your camera. If you want to double the sensor’s sensitivity to the available light then the number will double. 100 to 200, 200 to 400, 400 to 800, and so on. Each doubling equals another stop of light and will increase your exposure.
- Bright Sun or Snow- ISO 100
- Cloudy- 200-400
- Indoors – 400-1600
- Dark Church – 1600-6400+
How can I tell if the ISO is affecting the quality of my image?
The screen on the back of your camera can be misleading at times, and this is one of them. The brightness on your camera can change the appearance of the quality of your image. It can appear brighter or darker, which can change the way you actually edit the file once it gets on your computer. For example, if you think that your exposure was perfect in camera only to realize that you have to increase the exposure, you’re actually introducing noise into the shadows. Not in every case, but in some cases. The more the exposure has to be increased the higher your chances of having a noisy image are.
When you playback your image, zoom in and see if you can see sharp edges or if they are starting to get fuzzy and dappled with colored dots. This can be seen when you zoom in to 100-200% in Lightroom or your editing software.
Below is a 200% zoom on the photo above. The one on the left has not been retouched so you can see the colored dots and noisy appearance. The one on the left has had luminance and masking applied so that the noise is not as noticeable.
How can you fix this? Prevention and Practice really. Knowing what your camera is capable of and learning how to read your histogram instead of relying on the screen. More on Histograms in a following post.
Noisy images can be corrected using the Luminance slider in Lightroom and the noise reduction filter in Photoshop. But relying on these tools is never a good practice.