Have you been caught out by the brightness of the LCD screen? Have you taken a shot and then with a quick glance decided the exposure was correct and moved on? If so, you're not alone and what you may have found is that when you get back home, the image on your screen looks either much brighter or much darker than you thought it was from your quick glance.

Well, the answer is simple - the brightness setting of your LCD screen is throwing you off. 

Now, once and for all, here's a tip not to forget: You can't judge exposure on the LCD screen alone. You need to use the histogram. And your eyes. 

Now, the LCD screen on EOS cameras has a range of brightness settings. The EOS 5D Mark II for example has 7 levels to choose from. You should select the correct brightness setting for the lighting conditions you are in. It's not just a case of set and forget. If you're in low light and you set the screen brightness too high, you'll think images are brighter than they are. If you're in bright conditions and the brightness of the screen isn't high enough, you could end up over-exposing images - especially if you don't have the highlight alert enabled. 

The EOS 5D Mark II does have one other trick as well - an automatic brightness setting for the LCD screen. Now, this is all very well, but I find it annoying. The brightness is controlled by a sensor beneath the screen. Trouble is, you can easily cast a shadow over the sensor making it change the brightness of the screen, when in fact, you don't need it too. 

What's the correct brightness setting then? The answer is simple. When you look at the brightness setting screen, there is a grayscale next to an image. You should adjust the brightness setting so that you can determine each of the levels from black to white clearly, with the bottom level looking essentially pure black. And yes, this does mean doing it on a regular basis. From that point of view, it's actually quite a useful setting to put into the My Menu (green tab) settings on your camera so you can find it quickly. 

Even with the screen set correctly though, you still need the histogram to give you a good idea of exactly how the tones are distributed within the image and whether the exposure is correct or not. If it looks correct on the screen, but the histogram is all the way down to the left, then unless it is a very dark scene, your image is probably under exposed.