Now don’t get me wrong some situations can trick your cameras light meter. However, when first learning to get your camera into manual mode I believe the light meter is your best friend.
In an article over at Digital Photography School author Simon Ringsmuth covers how to master manual mode by using the light meter.
Most cameras have a few different shooting modes such as Automatic, Aperture Priority (A or Av), Shutter Priority (S or Tv), and Program. It’s not uncommon for people to take a majority of their photos in Automatic mode since it generally does a good job of getting decent results, though more advanced photographers will often use Aperture or Shutter Priority. Shooting in Manual, however, might seem intimidating and highly complex but once you understand a few basics it starts to make a lot more sense. Certainly you should have a working understanding of the three components of the exposure triangle: shutter, aperture, and ISO.
But in order to get the most out of your camera you will need to know how to use a simple, but incredibly powerful, tool that functions as the glue that binds everything together: the light meter.
Nestled quietly at the bottom of your camera’s viewfinder or Live View display is a small block of lines or bullets accompanied by a few numbers. You might also have noticed a little triangle moving back and forth, or some vertical hash marks appearing and disappearing from time to time, in a fashion that seems nonsensical or completely random. If these numbers and symbols make no sense at all, don’t worry, you are not alone. It can be a bit confusing to understand the light meter at first. But once you get the fundamentals you will probably find yourself growing much more confident in understanding how photography works. Maybe you’ll even venture out of Automatic and into Manual for the sheer amount of control you are able to have over your photos.
Before I get into the nitty gritty of the light meter itself, I want you to take a look at it in relation to the other data shown in your camera’s viewfinder. Note that this diagram is highly simplified and your viewfinder might look slightly different, or include other information, but all cameras (except some point-and-shoots) include the elements shown here.
In this example the camera’s shutter is set at 1/90 of a second, the lens aperture is f/4.8, and the ISO is 400. The light meter is a readout that shows whether these values are going to result in a photo that is properly exposed – that is, a photo that is neither too light or too dark. The small triangle hovering over the zero in the light meter shows that the exposure is correct, and when the shutter button is pressed the picture will look fine. But, I’ll show you a few pictures to see what happens as the camera’s exposure settings are changed. If you want to try this yourself you will need to have your camera in Manual mode, and I would recommend reading the rest of this article with your camera at your side so you can do a bit of experimenting on your own.
Source: Digital Photography School
Image Source: Luz Adriana Villa