There are three settings that you need to know to get a correct exposure in manual mode.  The first one I will review is your camera’s ISO setting.  The other two settings are aperture size and shutter speed. I am starting with ISO, since ISO is the simplest to understand and it typically it doesn’t need as much adjustment as aperture and speed.  You may set the ISO a handful of times for an entire afternoon, but may need to change either the aperture size or shutter speed for nearly every shot.

ISO Is Sensitivity
ISO stands for International Organization for Standardization, for those of you who need to know.  It represents the sensitivity of your camera’s sensor.  So when you adjust your ISO, you are adjusting the sensitivity of your sensor. Note, this is a quick guide to shooting manual with a digital camera, however, ISO is also used to describe the light sensitivity of traditional film.

ISO Settings
ISO settings can range from 100-400 or greater on digital point and shoots, while they can go as high as 3200 with some digital SLR models. The slowest ISO is usually 100 and doubles, up until your cameras limit, i.e., 100, 200, 400, 800, 1600, 3200 … Some models will have other “special” ISO settings for particular settings, check your manufacturer’s manual to see what they do and when to use them.

What It Does To Light
When you adjust the ISO you adjust your sensor’s film sensitivity, a higher number means the sensor is more sensitive. A more light sensitive sensor means that you can capture an image faster, all other things being the same. Although, that may sound great, like all things photography there is a trade-off. The higher you increase the sensitivity, the more noise will appear in your images.

Relatively speaking, each successive number doubles sensitivity, so that ISO 200 is twice as sensitive as 100 and half as sensitive as 400. This increment in light is called an f-stop, a term used to describe aperture sizes; so that each successive ISO is an f-stop brighter than the last. More on f-stops later when I discuss aperture sizes …

What Else It Does
With a camera set at 1600 or 3200 ISO you can shoot great shots in dark and low light situations without the use of flash or tripod, but you will have a lot of noise in your image, and even though it would probably make a great 4 x 6 or 5 x 7 print, the noise would become more and more unacceptable at larger print sizes.   So if you are out with friends at night or indoors and just have to capture the moment, go to 1600 or 3200 if your camera is capable. However, if you want to make a large, framed print, you should think twice about shooting above 400 or 800 ISO.  Of course, maybe you prefer the grainy look for certain situations, or maybe that’s just your thing – so be it.

How To Set ISO
Generally speaking you should choose the lowest ISO that is possible under the lighting circumstances. By keeping your ISO setting low, hopefully at 100, you will be able produce clean images that can be blown up to 16 x 20 or larger. Of course you also have to set your aperture size and shutter speed correctly, but a low ISO is the first step. There will be situations where it may seem impossible to keep the ISO low, but there may be other options or workarounds, such as flash(es) and/or tripod. But that’s enough for now, you’ll get a better idea about those things after you read about shutter speed and aperture size.   By now you should understand what ISO means and what it does to your images.

Coming Next
Stay tuned, I will be writing about shutter speed next, aperture size after that, then I will explain how the three (ISO, speed, aperture) interact, although by that time you should be able to guess most of it.