Let's review a little:
Lesson #1 was about which end of the camera the light goes in and where it goes once it's inside.
Lesson #2 was about using a camera's shooting modes to CONTROL aperture or shutterspeed.... or nothing ... or everything.
Lesson #3 was about making your photographs have IMPACT by using good composition.
Now it's time to tie all of it together with some discussion about tradeoffs. Photography - just like life - is full of tradeoffs. This lesson and the next two to follow will be all about photographic tradeoffs......
Remember that there were three important parameters that needed to be chosen for each photograph in order to get a good exposure: ISO, aperture, and shutterspeed. In this lesson, I'm going to show you the tradeoffs that are associated with ISO. I'll start with a brief description, then I'll show some examples of photographs that illustrate the tradeoffs. You'll see how these tradeoffs happen in REAL LIFE!
Let's start with ISO....
Remember that ISO is all about the sensitivity of your sensor - or film, if you've not yet made the switch. An ISO setting of 100 is half as sensitive to light as an ISO setting of 200. Likewise, 400 is twice as sensitive as 200, and 800 is twice as sensitive as 400. Some cameras go all the way up to 3200 and 6400 ISO. The higher the ISO number, the more sensitive it is to light.
So when do you need your sensor to be more sensitive to light? There are two answers: (a) when there's NOT much light and (b) when you don't want to use much of the light that is available. Lowlight situations like during a church service are an example of the first. Sports photography when you want to stop the action with a super fast shutterspeed is an example of the second. Indoor sports photography inside poorly lit gymnasiums is a double-whammy. In that case there's not much light available AND you want a fast shutterspeed to stop the action. That's when you'll have to crank the ISO up as high as it will go.
So what is the tradeoff? Why not shoot at a high ISO all the time? Because of digital noise.
Back in the old days with film, the higher the ISO - the grainier the photograph would be. With digital, we have the same problem. High ISO leads to more digital noise. The good news, however, is that in the last few years the camera companies have gotten very good at managing digital noise. The Canon 40D camera that I use now gives me photos at 3200 ISO that have about the same amount of digital noise as my old Canon Digital Rebel had at 800 ISO. That's a huge difference! Yay Technology!
Tradeoff #1 - ISO - Higher ISO lets you shoot faster shutterspeeds and with less light but it may result in more digital noise.
Here are some examples:
This first shot is of a young lady playing guitar in a very low-light situation where I had to shoot at 1/100th of a second (fast enough to keep her moving hand from being blurred) with the lens aperture at f/2.8 (wide open) and with the ISO set to 1600 (as high as it would go on that camera.) The result is a very nice photo when you look at it this size.
But if you were to enlarge it very much, you can begin to see the GRAININESS in the photo. That's digital noise.
Another pair of examples: Different young lady, ISO at 100 (1/16th as sensitive as ISO 1600) in a brighter setting.
Enlarge just her face and..... very little GRAININESS ..... very little digital noise.
Now, did I say GRAININESS is bad? No way! There are times when digital noise can add a certain artistic look to a photograph. You also must keep in mind whether or not the photograph will be enlarged. I shoot lots of sports photos at high ISO that would make very grainy posters. But most of my customers buy 4x6 prints! Graininess and digital noise are much less important on the smaller uncropped prints.
My point is NOT to teach you to avoid digital noise or graininess but to KNOW when to expect it and decide for yourself if it's okay in each situation. I personally like the first photo of the young lady playing guitar and I think the digital noise doesn't hurt at all. Why? Because it gives the photo IMPACT and that is something we learned to work toward in our last lesson. A grainy photo taken in a coffeehouse setting under the warm glow of stage lights: very cool!
Now that you understand ISO, you know what to expect when you change it. It's a tool in your camera bag that you can begin to use effectively.
Go shoot some photos. Mess with the ISO settings on your camera and watch what happens to your photos. Good Luck!