In photography, there are a few key variables in determining exposure. The first is the aperture of the lens: basically, how much light is let in. Really serious (or rich) photographers carry around very “fast” lenses–they’re enormous and let in a ton of light. Notice the huge lenses that you see on the sidelines as sporting events, for example. (Err, not the length, but the width–these things are huge in both dimensions.) Of course, these lenses (we call them “fast” lenses, or lenses with wide apertures) are very heavy, and insanely expensive: for a really good one, you’d pay at least $1,000, and that’s pocket change compared to some lenses.
Another control is ISO sensitivity. Back in the days of film, some film was more sensitive to light than others. For example, ISO100 produces great pictures, but requires a lot of light. It’s superb for outdoor pictures on a sunny day. On the other hand, if you’re getting shots indoors, you might be at something like ISO1600. The problem is that, as you increase the sensitivity, you also increase the noise. ISO1600 will get decent shots indoors, but they’ll be grainy. (This is especially bad if you’re like me and tend to try to boost details in the shadows in Photoshop.)
The two come together to control the third important variable, shutter speed. In some cases, it doesn’t matter a ton. If it’s bright and sunny, and I’m taking a picture of a building, I really couldn’t care whether it’s 1/100th of a second or 1/4,000th of a second. And, if I’m using a tripod, it’s not uncommon to have shutter speeds lasting several seconds. But the problem is that, if the shutter speed is too low, you get a lot of blur. There are two reasons–the first is that people rarely hold still. I use 1/60 as a general rule of thumb: below that and you risk some blur if people are moving a lot. This is a really rough guess: I’ve gotten great portraits at 1/8, and sometimes 1/125 isn’t fast enough.
The bigger consideration, though, is camera shake, especially with longer zoom lenses. The rule of thumb there is 1/length. For example, shooting with a telephoto 200mm lens, it’s recommended that I shoot a 1/200 of a second or faster.
Putting it all into practice… Bill Clinton was speaking tonight at an event we went to. I have a 55-200mm telephoto lens, and tended to stay right around 200mm. I stayed at ISO1600; I can go to ISO3200 but it’s very grainy so I don’t use it. Unfortunately, though, my lens can’t go wider than f/5.6 at that length, which meant that the fastest I could get shots was around 1/60th of a second. At 200mm, this really was inadequate: most of the shots came out okay because I have a steady hand, but they’re not all that sharp. Example:
It’s okay, but now compare it to this picture:
Granted, the subject isn’t that interesting, but every time I see that shot I took, I think, “Wow, that’s sharp!” Not so for the Clinton photo. If you view it in larger detail (click on it), its subtle blur becomes increasingly obvious.
There was a professional photographer about ten feet away from me. She was shooting a 70-200mm lens, which is a similar length to mine. But hers is an f/2.8 lens, which lets in twice as much light as mine does. So while I was getting 1/60 shutter speeds, she could have been getting 1/120. (Hers had Image Stabilization, too, but that’s a story for another day.)
The thing is, taking telephoto portraits indoors isn’t all that rare of a thing to do. To get good shots, you need to get that shutter speed up. There are two ways to do it, as you should now know: raise ISO or get a better lens. The problem is that getting a better lens will set me back $5,000 or so. And it’s an insanely heavy lens as well.
The other option is one that, until recently, wasn’t feasible: raise ISO some more. ISO1600 is good. You can do ISO3200, but it’s decent on only a few cameras. But I really have to give Nikon credit with their D3. It’ll go to ISO25600. Check out some samples. I’ve seen some higher-res images at ISO6400, and it’s just about perfect! Its ISO6400 rivals my ISO1600. The thing is, that’s a huge increase to be able to shoot at 6400 and have a perfectly usable image. It would have helped a lot with getting better shots.
I truly hope this is the direction camera makers go in now, and that Canon and Nikon get into an “ISO war” trying to outdo each other.
