Welcome back for the third and last part of the beginners guide to your camera series. This part I will focus on the ISO setting and how it effects your photographs. If you have not read the other parts in the series I recommend you do so. I explain a few basics as well as the aperture and shutter mode.
ISO is a numbering system created by the International Organization for Standardization to represent the sensitivity of film negatives. Film sensitivity may also use a scale created by the American Standards Association or ASA however most digital cameras now call the setting ISO. There is a bunch of complicated math that goes into figuring out the ISO number for a sensor or file negative. However your digital camera will come with several predetermined levels for you to select.
The lower the number the less sensitive the sensor will be in your camera. The trade off for using a low number is that your images will contain less noise. This is the same for digital photography as it is for film photography. Film negatives work by suspending silver particles in an emulsion. Those silver particles absorb light and when put through a chemical process produce a film negative. The way to create a most sensitive film negative was to create larger silver particles. Those would then absorb more light faster and allow for less exposure time. The larger particles created a grain or noise in images because they are more distinctive.
Enough about film, you get the same effect when you crank up the ISO on your digital camera. The real difference is that film noise can really add style to a photograph where it just looks bad in a digital image. Most cameras use a smoothing / sharpening algorithm to eliminate the noise after you take an image. That the noise ends up taking away more than it adds.
Using the ISO
Unlike in the previous articles there is no ISO mode. If you can change your ISO it will be in a setting or menu. Most cameras also have an automatic mode however I recommend keeping your camera at its lowest ISO setting unless you will be needing the higher sensitivity. The pros of keeping your camera at a lower sensitivity is that you will get cleaner and smoother images. You will get the sharpest images your camera can produce. As you start to crank up the ISO you should notice the slow addition of noise to your images. Most cameras have a point in the scale were things get exponentially worse. This comes from the way the ISO works, each notch in the scale is twice as sensitive as the one before it. So ISO 200 is twice as sensitive as ISO 100.
How the ISO effects images
Because the ISO makes your camera more sensitive to light it effects all the other settings on the camera. With a higher ISO you can shoot at faster shutter speeds with the same aperture. This would work well for indoor images or low light situations. If you know your camera does pretty well between ISO 100 and 800 then you can crank up the ISO while shooting indoors. This will allow for a faster shutter speed and create images with less blur. Essentially it acts as if your camera is receiving more light. This is going to greatly depend on what sort of camera you have. Digital SLR style cameras handle higher ISO settings better because they normally have a larger (in scale not megapixel) sensor, allowing for more surface area, than a point and shoot camera.
The ISO is not as important to understand over the other settings described previously. Once you have a handle on the shutter and aperture you will notice the effects of the ISO more.
I hope these articles have helped you better understand your camera as well as take better photographs. This is just be beginning, the real learning comes from experience. So get out and play with the settings, take several photographs of the same thing but only change one setting. Try using the full manual mode and have some fun.