I almost forgot about the 4th factor that makes up for a good exposure – the ISO speed. I won’t go into what the acronym stands for as it does not, in any way, have anything to do with how you’re going to use it for your photography.
Anyway, the ISO speed is the sensitivity of your film (for film SLRs) or sensor (for digital SLRs). The higher the ISO number, the higher the sensitivity to light. However, you also have to remember that the higher the ISO, the grainier (in terms of film photography) or noisier (in terms of digital photography) the image becomes.
With this in mind, higher ISO ratings work better with dimly lit areas or night shots where you don’t have a tripod to stabilize the camera or a flash unit to use for lighting. By choosing a high ISO number, you expose the film or sensor to as much available light as possible. On the other hand, bright, sunny days merit a lower ISO speed as they are less sensitive to light.
In terms of film and digital photography, you have the freedom to change ISO ratings at any given time with a digital camera, as opposed to a film camera where you’d have to swap our film rolls of different ISO ratings.
Also, you need to understand that you ISO setting will have an effect on your shutter speed-aperture size combination. If at your current ISO rating, the shutter speed appears to be too slow that you can’t avoid shaking while hand-holding the camera, the aperture is already at its biggest opening, and you cannot use a flash, switching to a faster ISO speed can you give the option to use a faster shutter speed.
Don’t be afraid to play around with your camera’s ISO settings and pair it up with different aperture openings and different shutter speeds to get a feel of what I’m talking about in here. Try practicing in a shaded area or try some night shots while you’re at it. After all, there’s no better way to learn than by trying it out yourself.
