Building Blocks of the Photographic Process: ISO

Posted by on Sep 13, 2013 in Photography | Comments


We’ve already developed a better understanding around shutter speed and aperture when it comes to making a proper exposure in photography. Today we’ll dive further into the foundations of the photographic process, covering ISO.

Handing Holding Camera Ready to Shoot

ISO is rated by sensitivity to light.

ISO 100 is less sensitive, 400 is more sensitive, and 1600 is very sensitive.  It’s interesting to note that digital ISO is much the same as it was for film cameras. Higher ISO films were quicker to record light but had the disadvantage of graininess. In the digital age, higher ISO settings are also quicker to record light but lead to digital noise. By cranking up the ISO on your digital camera, you decrease the number of photons that are recorded accurately due to increased heat and electrical activity — and this gives you noise.

Digital noise is almost never something we want in our photographs, so a general rule of thumb is to use the lowest ISO setting you can.

I like to start at 100 (as low as my camera will go) and then decide what my shutter speed and aperture need to be. If I can’t get my aperture any wider or my shutter speed any slower and still get the image I want, then I’ll start to crank up the ISO. Sometimes, the digital noise is a compromise you have to live with in order to get your shot.

ISO Measurement Chart

Reference this chart when adjusting your ISO.

Like shutter speed and aperture, ISO is measured in stops.

It’s an easy system to figure out: 200 is twice as sensitive to light as 100 and 800 is four times as sensitive as 200. The ISO scale measures in full stops would look something like this: 25, 50, 100, 200, 400, 800, 1600, 3200, 6400, etc. Some cameras will do extreme ISO settings like 25,600 for dark situations where you need a lot of sensitivity to light. This is helpful, but also typically comes with a lot of digital noise

Under normal conditions, with practice, you will have a good idea of what kind of ISO settings you need to have.

For example, outside on a sunny day ISO 100 is almost always the best setting. Shooting indoor in a place with windows you might go up to ISO 400. Shooting in a room without windows and only light fixtures lighting up your subjects you might go up to ISO 800. Shooting wedding photography in a dark church probably means you are going to be using ISO 1600 or 3200, if you aren’t using a flash. Of course, these settings depend on your shutter speed and aperture, but as you shoot in different situations, you’ll know where your ISO settings need to be.

Black and White Photo of Wedding Couple at Alter

This is a dark church at ISO 3200. Many modern digital cameras have relatively low noise at high ISO.

In addition to camera manufacturers making higher ISO less noisy with each new model, there are software companies that have created noise reduction software to clean up images that are shot at higher ISO.

Color Detail Photo of Wedding Couple at Alter

Straight out of the camera without any noise reduction

Clearer Color Detail Photo of Wedding Couple at Alter

Using the Noise Reduction feature in Lightroom

Adobe Lightroom has great noise reduction features to make an image cleaner and sharper. I also like using Nik Software’s Dfine to get rid of some of the graininess in high ISO photos. The ability to take away noise in a photo in post can change the way you create your exposure. Knowing I can compromise on a low light image by adjusting my ISO rather than my shutter speed or aperture, without much change in overall image quality, is huge.

What’s the highest ISO you’ll go on an image before the quality is too low for you to be happy with it? Do you have any noise reduction tricks?