How to use the Light Meter and Exposure Compensation function

In my last post, I discussed how beginners like me learn to use the manual mode in our camera. However, I realized that, in order to understand the concept fully, we must learn how to use the in-built light meter of our camera. In this post, lets shed a bit more light on questions like, What is Exposure Value, how to read EV meter and what is exposure compensation. These things are critical to a photo and if your exposure is not right, then even a potential award winning photo will look blah.

Exposure Value

If you want a geeky answer to what is exposure and want to learn complex formula consisting of various Latin alphabets, head over to Wikipedia. But if you are like me and want a simple idea, just keep in mind that exposure simply means the amount of light allowed to fall on the sensor during taking a photo. So a properly exposed photo means one where everything is well illuminated without burning or darkening something. Over and under exposed photo means excess light and inadequate light respectively.

So now you know that Exposure is about the amount of light allowed onto the sensor which determines the brightness of a photo. Now, the next question, "How do I know what is the correct exposure for a photo?" This is where the EV meter comes into play.

EV Meter

EV meter is the built-in light meter of a camera. It analyses the amount of light coming in through the lens and determines what should be the correct exposure for a photo, by a very complex set of algorithm and preset values. The EV meter is displayed on the top LCD panel or the back LCD panel depending upon your camera model and on the optical viewfinder. It looks something like this-

                                             + I . . I . . I . . 0 . . I . . I . . I -
                                                 3     2     1               1     2     3
with a little arrow below the diagram or some bold bars will fill the dots (Depending on your camera model). The I in the diagram denotes stop and the small dots in between them are 1/3 rds of a stop. When the meter shows inclination towards the negative side (right side), the picture will be under-exposed and when the meter shows inclination towards positive side (left side), the picture will be over-exposed. The ideal scenario is when the meter shows exactly at 0. You can increase or decrease the amount of light available by changing the aperture, shutter speed and ISO, as discussed in the earlier post here. One quick point, increasing one stop in the meter means doubling the amount of light and vice-versa.  However please keep in mind that the meter is showing only what the camera thinks as perfect exposure. If you want something different/unconventional, then this metering wont be much effective. In those situations, take a picture at 0 EV  analyze the picture and increase/decrease light as you want.

So in nutshell, take picture when the EV meter is showing 0 for perfectly exposed photos, in most of the circumstances .

Exposure Compensation-

The above statement is correct, but as I said, in most of the circumstances. The camera makers are not God however and no matter how much the technology evolves, we have to interfere sometimes to get the desired results. Lets not get into technical details about how a camera light meter works (google can answer better than a novice like me anyway), but just remember that when the lighting is challenging and/or when the scene is predominantly bright or dark, the camera meter will be fooled. Suppose we are trying to shoot someone wearing white cloth in snow. The camera meter will get fooled by the white tones and will try to compensate that by allowing in lesser amount of light. As a result, if we take a picture according to the light meter, the image will be under-exposed. In those circumstances, we have to apply some amount of exposure compensation. There is no fixed formula here and as we keep on shooting, our understanding regarding exposure will keep on getting better and better.

Tweaking the exposure when we are in Manual mode is very easy. All you have to do is to adjust the three variables to get the desired result. Its even simpler in other modes. If you are shooting in P mode, or S mode or A mode, you can change the EV simply by pushing the Exposure Compensation button in your camera. The camera will automatically do the required settings to change the exposure.

However, what often confuses people is function of Exposure Compensation button when we are shooting in manual. Inputting exposure compensation has the exact same effect in manual mode as it does in any automatic mode. It just biases the lightmeter by +/- n stops, and adjusts the *recommended* shutter speed or aperture displayed in the viewfinder by that amount of compensation. The difference is that in any automatic mode the camera selects and applies that shutter speed and/or aperture automatically, while in manual mode you need to manually select those inputs to "zero" the meter.

Say you are shooting at the beach on a bright sunny day, and you know that you will want to overexpose all of your manual mode shots by +1 stop so that the scene is rendered correctly. If you set your exposure compensation to +1.0 EV, when you have manually selected a shutter speed and/or aperture so that your meter reading is zeroed/centered, you know that your shots will be properly exposed (at +1EV) for the bright, sunny beach scenes.

So, don't get confused with the EC button while shooting in manual. Its better to adjust the values manually. Otherwise, there is a very high chance of getting confused and end up with over/under exposed photos.

I am attaching a video here for easier understanding of the matter-

 

In my next post, I shall write about something I should have written earlier. Its about the various shooting modes in a DSLR. Till then, b bye...