These days cameras come with lots of modes. Aperture priority, shutter priority, manual, sports, portrait, landscape, macro and on and on and on.
You know what? I only ever really use one of them. And that's Aperture Priority. Known as AV on the Canons (stands for Aperture Value) and A on pretty much every other brand, the photographer chooses the aperture and the camera will automatically choose the shutter speed for you.
So why do I pretty much always use this? Because for the style of work I do the aperture is pretty much the most important thing because it controls the depth of field.
Take this image here. Now I'm focussed on the eyes of the Buddha at Boudnath Stupa in Kathmandu. In front of it are a series of prayer flags. Now imagine what this image would look like if the prayer flags were just a blurry mess of jumbled colour with no shape. Not only would you have no idea what they are but they would be really distracting.
By choosing the right aperture I've ensured that they're sharp enough that you can tell what they are, which helps contribute to the story.
But what about when you want a fast shutter speed? Don't you use shutter priority? Well, no I don't. For a couple of reasons. One is that the camera can trick you. It assumes that once you come out of idiot mode you're not an idiot. And the problem is that sometimes we all are. :)
You see the problem with Shutter Priority is that if you choose a really fast shutter speed to stop some action, say 1/8000th of a second, but there's not enough light to let you use that fast a shutter speed the camera will still let you take a picture. And what will that picture look like? Well it'll be pitch black basically. The only warning you have that there's not enough light is a flashing warning. On the Canons the aperture flashes, on the other brands you get a message such as Low flashing at you.
I'm here to tell you now that in the heat of the moment you're not going to notice a flashing warning. Anything short of a mallet coming out of the battery chamber to whack you in the head will not help you. So in order to ensure I always get a fast shutter speed I leave the camera in Aperture Priority mode and open up to my widest aperture - usually f2.8.
If you remember back to Photography 101 a big aperture will give you a fast shutter speed so if you open up to your biggest aperture you'll ensure that you always have the fastest shutter speed you can get for the lighting conditions.
Of course some cameras have what's called a Safety Shift function so that if you choose too fast a shutter speed for the conditions it will automatically default down to the fastest shutter speed possible so that's another option if you have it. If you don't then Aperture Priority is the trick!
Besides leaving it in Aperture Priority all the time means I don't wear myself out having to turn that little dial all the time. :)