Today's DSLRs can display a histogram (which is a graphical reading of the tonal range of your photo) right there on the camera's LCD monitor, but if you don't know how to read one (or didn't know it's there), it doesn't do you much good. I only use my camera's histogram for one thing, and that's to make sure I haven’t clipped off any important detail in my highlights. So, what am I looking for when I look at my histogram? Two things: (1) I don’t want to see the histogram's graph touch the far right wall. If any of that graph hits the far right wall, I'm losing detail. So, what I'm really hoping to see is (2) a small gap between the end of the histogram and that far right wall (as shown above). If I see that gap, I know I'm okay, and that I'm not clipping any highlights. I can look at my histogram and immediately see if this has happened, and if I have clipped off important highlight information, I will generally use the exposure compensation control on my camera to override what my camera read, and lower the exposure by 1/3 of a stop, then I take the shot again and check my histogram. If I'm still clipping, I lower the exposure compensation to –0.7 and then shoot again, and check again. I keep doing that until my clipping problem goes away. Now, the histogram can only help so much, because what if there’s a direct shot of the sun in my photo? That sun will clip big time, and there will be no gap, but that's okay, because the surface of the sun doesn't have any important detail (well, at least as far as I know). So the histogram can help, but it's not the bottom line—you still have to make the call if the area that's clipping is (here's the key phrase) important detail, so don't get hung up on histograms—at the end of the day, you have to make the call, and the histogram is just a helper, not your master.