ISO settings in digital photography, an illustration

In a previous post about aperture value, my friend Ting asked about ISO settings in the comment thread. Okay, so last night I was standing on the sidewalk of a narrow street behind Sam’s dorm (Alex threw me out of the car because I was smoking) waiting for Sam to collect her stuff (dirty clothes, laptop and whatnot) when I remembered Ting’s comment about ISO settings. The environment was just perfect to illustrate what the ISO settings mean.

Back when everyone was using film, every film box was labeled with a particular ISO — 100, 200, 400, 800… The number refers to the sensitivity of the film to light. The lower the number, the less sensitive the film to light and, ergo, the finer the grains in the photo. “Grains” refer to the visible white spots that make a photo look blotched. Films with lower ISO are used for outdoor/daylight photography while those with higher ISO are preferred for indoor/low light photography as well as for sports photography.

In digital cameras, you can choose and change the ISO speed with every photo you take. ISO 100 and 200 are best for outdoor/daylight photography while the higher settings are best for indoor, low light and night time photography. At least, that’s the general rule. The thing is, while a dark scene will appear brighter with the higher ISO setting, the more blotchy it appears too.

I know. The techie lingo can turn anyone off. So, here’s a visual explanation and illustration. Photos #1 thru #4 were taken with a uniform aperture value (f/3.2) but with escalating ISO settings. The flash was off.

Above, left, ISO setting is 200. Above, right, ISO setting is 400. Notice the tall building in the background and how it is more visible and better outlined with the ISO set to 400? Will the photos look better with ISO settings higher than 400? Let’s see, shall we?

Above, left, ISO setting is 800. Above, right, ISO setting is 1600. Grains are starting to show at ISO 800 — look closely and you’ll see them. At ISO 1600, you don’t have to look hard — the grainy appearance is very obvious.

Why the grainy appearance? It has to do with forcing faster shutter speeds. Which, of course, sounds too technical again and that might give you a headache (and me too if I am forced to explain in technical details).

The obvious question is whether by changing the aperture value, the photos will look better. Let’s try that.

The two photos above were both taken with an aperture value of f/8.0, the one on the left with a setting of ISO 800 and the one on the right with ISO 1600. Compare them with photos #3 and #4 which were taken with the same ISO settings but with an aperture value of f/3.2. Photos #5 and #6 are grainy and dark. Photos #3 and #4 are grainy but the lighting is better. Imagine how the scene would look if the photos were taken with an aperture value of f/8.0 or higher and ISO settings of 400 or lower. Only the lights from the electric posts and buildings would be visible.

So, let’s just stick with the bottom line — if the lighting is good, lower ISO settings are your best bet.

If lighting is low (eg. indoor or night time), you can still keep the ISO setting low, combine it with a wide aperture setting AND use a tripod to avoid blurring. Why a tripod? A higher ISO setting means more sensitivity to light, right? Hence, the more sensitive to camera shake as well. The slightest shake and blurring will occur.

Another option is to use the flash, naturally. Might work if the subject is a short distance from the camera but with landscapes and cityscapes, it won’t work because the flash won’t reach as far the mountains or buildings so many meters or kilometers away. Besides, unless you have a good diffuser to make the flash bounce so that no harsh lights are cast on the subject, the lighted portion of your photo might look unnatural.

Everything, of course, is relative. Which combination of aperture and ISO settings is best depends on what the subject of your photo is, how much light is available and what effect you want to achieve. So experiment, experiment and experiment some more. The more familiar you get with your camera’s functions, settings and capabilities, the better photos you’ll be able to take.

By the way, all photos were taken with my Canon G10.