histograms are only IMHO useful in “double checking” your particular subject that you’ve metered, and only if that subject completely dominates the frame eg. zooming in on grass (“0″ ev), or a white dress (+1.7 ev) or a grey card(generally “0″). Check the spike in the histogram, if it correlates to your metered value, then you should be good to go.
I use histograms all the time to check for horribly wrong exposure. It’s like an engine dummy light… it doesn’t tell you if your car is running right, it just tells you if certain parts have gone horribly wrong. The histogram is especially useful when shooting portraits and your camera can split the channels, because you can easily be deceived by the LCD when you blow out only one channel.
When setting custom white balance and shooting a gray card, I can use my camera as an incident meter by making sure the spike is centered. If the light is consistent, you can simply adjust manually to the light so that the spike is in the center, and then you know you have “proper” exposure. Not balanced, not flat, not maximizing tonality, but actual proper exposure.
It’s also possible that you don’t want proper exposure, but instead want to maximize the information in an exposure. Someone (Eggington?) alluded to this earlier. The histogram is invaluable for this, and it’s far easier to simply overexpose until the highlights hit the right side of the histogram than to use a spotmeter on all the bright areas of a scene. Note that “Exposing to the Right” is not about getting proper exposure. It’s about getting the most information possible onto your digital sensor for the SOLE PURPOSE of minimizing noise in the darks or preserving detail in the lights. It’s just a modern adaptation of the Zone system where you would expose your negatives for the shadows. Of course, it generally results in poorly-exposed pictures which need to be adjusted back to the proper exposures, but they will have less noise and more detail if done properly.
edit – @browneyedgirl
After reading all the posts in this thread, I think the best thing for any of us to do is to use both or all methods available for exposing. I will for sure be checking my histograms from now on. Less trial-and-error that way I think.
Checking histograms (or the LCD) is trial and error 🙂
There’s technically only one proper exposure, and that’s easily determined with an incident light meter near the subject, or histogram on a gray card. (The histogram is only relevant to proper exposure if you have a reference, such as a gray card.) The histogram, however, can help you preserve detail, especially if you push the highlights to the right side. But remember that this is not necessarily “proper” exposure, and is best used when shooting in raw, and will almost always require subsequent editing. (JPGs will make other adjustments that can mess you up, primarily white balance, contrast, and sharpening.)
But yes, make use of all your tools to get that picture. Even if you have to set it in P mode and have a reason for it, go for it.