9. How to Take Photos 4: ISO

Almost all this information comes from lessons by Chris Bray, including the photo examples.

ISO is a setting that determines how sensitive your camera is to light. ISO stands for the International Organization for Standardization, a group that develops various standards in business and technology, so that it’s easier for different countries to conduct business. The ISO was founded in 1947, is centered in Geneva, Switzerland, and still exists today, with 167 member countries and thousands of different kinds of standards in all engineering and scientific fields.

In 1974, the ISO determined a standard of film sensitivity to light, so that all photographers would know which film is best for which lighting conditions. Before the ISO standard, photographers relied on two different systems, one set by the ASA and one by the DIN. It was confusing, so everyone agreed to switch to the ISO. This is the system we still use today, even though most cameras don’t use film anymore––digital cameras emulate the same sensitivity as traditional film with a setting you can cycle through, as if you were switching different rolls of film (you used to have to change a roll of film to change your ISO). Note, all these film rolls below have a different ISO number on them:

If you're using a 35mm film camera, you may see a dial that asks the ISO of the film. Whatever number is on your film - be sure to set the dial to that number above, so the camera "knows" what film is inside it.

Digital cameras use the same system and numbers as traditional film (because for years, photographers were more familiar with it). ISO ranges from 100 (for bright lit settings) to 6400 for traditional film, and can go much higher for digital cameras - some over 51,000.

100 is for very bright conditions, typically outdoors in snowy or highly reflective areas.

200 is also for outdoors, on sunny days.

400 is for grey days outdoors, and well-lit interiors. This is a good, general purpose ISO.

800-1600 are for interiors.

3200 and above are for darker, nighttime places and dark interiors.

Most newer digital cameras have an option for AUTO ISO, where the camera decides which setting works best. You can use that and check the results in your view screen. If you don't like it, you can always switch it to a specific number. AUTO ISO works fine in TV mode, but not so much in A mode (see more in this lesson). The ISO will make the photos just fast enough to eliminate camera shake, but fast moving objects like a bird’s wings may still come out blurry. In some cameras, you can also set a minimum shutter speed, for example 1//500s, or faster, to help reduce/eliminate motion blur.

ISO, Aperture, and Shutter speed make up the exposure triangle, the three main settings that determine how your photograph looks:

Of the three, ISO is the only one that doesn't have a big creative impact on the picture, it only scales it from lighter to darker. The best way to think of ISO is an extension of your shutter speed. Usually, you can ignore ISO all together. A lot of basic shots are done in middle lighting, in which you set it to 400 and it should be fine. But, you might find in lower light that you can’t get a fast enough shutter speed, in which case, you just crank up the ISO a bit and take those faster shots.

You should know that your camera is programmed to try to find the value of light as a grey mid-tone, and it will look for that, no matter what you're shooting. So, if you use AUTO ISO, and you shoot something really bright, like a white piece of paper, or a white bunny on a white background - the camera will over compensate for this brightness, and under-expose your shot, making it look darker than you want. Lowering the ISO can help.

If you want to take some shots with a really fast shutter speed, for action shots, even during the day in bright light, a higher ISO will allow you to take those really fast shots, to capture things like humming birds or insects in motion, or a bird swooping down to catch a fish in the river. You might be in TV (S) mode, but raise the ISO to 800, 1600, or higher.

1/500^th of a second is still too slow for this bird

Raise your ISO and start taking 1/4000^th shots

Changing the ISO helps at night too, because it helps where a tripod can’t. Even if you’ve set your camera on a tripod and gotten out all the camera shake, if anyone’s moving in the picture, they’ll still be blurry:

Raise your ISO, and your shutter speed gets so fast you’ll get crisp sharp photos and won’t even need a tripod. Now, beware! If you raise your ISO too high, you get “ISO noise” a grainy effect:

This happens with both traditional film and in digital cameras, but for a different reason. You only notice it if you zoom in a lot, or print a very large version of it, but the higher the ISO, the higher the noise:

Fortunately, newer cameras are fixing this problem. Within 2 years of that Canon mk II, high ISO’s were already looking this much better:

So, test your cameras’ higher ISO settings for noise, and this will tell you what kinds of shots you can get. Because, shots like this you’ll only get with a good, high ISO:

There are features in post-production computer programs like Light Room and Photoshop that can smooth out photo noise. They can also adjust the exposure to lighten dark areas, although this is problematic. Every time you do this, you add "noise" to the image, you can lose detail, the skin color can shift and become unnatural looking or muddy. And correcting over-exposed areas is even harder. You can save yourself a lot of time and headache if you get the exposure right with your camera, as you shoot.