This isn’t new — I’ve watched people doing it wrong for years, from way before digital cameras existed. Only, I’ve just been on vacation, and that’s when one tends to see it more. You’ve seen it too, right? We all have.
I’m talking about watching someone take a picture of some huge thing that’s far away, and seeing the flash on his camera go off. [Foof!] The burst of light and the look of satisfaction at having snapped a good one is evidence that the user doesn’t understand why that’s bad (and why his photo might not turn out as he expected).
So I’ll tell.
First, it doesn’t do any good. We’re not talking about thousand-watt Klieg lights here; a typical camera flash just can’t illuminate anything very large, and the light from it isn’t effective at much distance. You can’t rely on illuminating something more than about 20 metres away (nor closer than about 1 metre), and it’ll work best between around 3 and 10 metres (but read the instruction manual for specific details about your camera). Think about that, and realize how close that really is. Use it too close, and you’ll drown your subject in too much light; too far, and you won’t be lighting the subject enough.
The corollary to that is that if the subject is larger than the image frame at 10 to 20 metres, it’s probably too big for the camera’s flash to be effective on it. I can’t tell you how many times I’ve seen someone photograph a large building, such as a church, from a distance of at least 50 metres, and watched their flash go off. And inside the church, if you’re taking a photo of a detail, the flash will do fine, but trying to photograph the entire nave and altar with the flash is pointless.
Of course, pointless isn’t bad. So, for why it’s actually bad, let’s continue.
Second, using flash from too far away risks having the flash illuminate some close-in objects that you hadn’t meant to highlight. You’ll often find that some nearby foliage, or a litter bin, or the arm of the guy just ahead of you to your right will be as bright as the sun, when you hadn’t even noticed its presence when you took the picture. This is usually not the effect you want.
Third, there’s the question of shutter speed. The camera is designed to synchronize the shutter (or the equivalent function in a digital camera) with the flash, usually by setting the effective shutter speed to 1/60 sec. That means that all the automatic stuff that your camera does is overridden by the decision (yours or the camera’s) to use the flash, and your flash photos will always be taken at 1/60 sec. Sometimes, that will work fine. Sometimes, it won’t. If it’s inappropriate to use the flash anyway, it’s better to have it turned off so the camera isn’t locked into a specific shutter speed.
Fourth, it runs your batteries down faster. Using up battery power on the flash is fine if you need the flash. But it’s silly if you don’t.
And finally, sometimes the use of flash is just rude, or forbidden outright. You shouldn’t usually use flash in churches, museums, theatres, and other such places. Maybe you’ll get bad looks from people. Maybe someone official will ask you to stop. Maybe you’ll be shown the door. Why subject yourself to that treatment (and others to your behaviour)?
Learn how to turn off your camera’s flash, and then do it. With a digital camera, especially, it’s better to set the default to be off, if you can, and to turn it on when you need it. If you wind up taking a shot without the flash by accident, you can just delete it, and re-take it with the flash on. (Most cameras have the default initially set to “auto”, and not all of them allow you to change the default. It’s annoying if you have to remember to turn off the flash every time you turn on the camera.)
My camera makes this particularly convenient: I have a Canon S3 IS, and in order to use the flash I have to flip it up. If the flash is closed, it’s off. If it’s flipped up, it’s on. Easy to choose, and essentially impossible to have it set the wrong way by accident.