First what is it ? The camera automatically make the picture at a defined brightness. If the picture darker, we say it is too dark, if it is brighter it is too bright.
This brightness equates to 18% grey if I want to make a brightness level for the whole frame. It means this bright color applied for the whole frame (picture) resembles the brightness of the average picture.
And this is usually mostly good for our purposes, but some cases not. Which are these cases ?
– Too bright scenes (beach without trees, snow) If the camera makes the white snow grey we use + exposure compensation until we satisfied what we see. (Usually between +1/3 – +1 EV)
– Too dark scenes (forest, or too much shadows) – Do you recognize that cameras makes too bright pictures in the forest ? This is why.
If the camera makes the forest too light, we use – exposure compensation until we satisfied what we see. (Usually between -1/3 – 1 EV)
– Night photography
– Special cases – there are many, for example man / woman in white clothes, here the camera makes the face dark, here + exposure compensation needed for proper face light level.
– Avoid burning up the sky – In very bright situations many camera has a tendency to burn up the sky, and in many reviews if you read the reviewers on big photography sites they note that.
For example the camera has a tendency to overexpose the shot. To explain a bit the camera cannot capture wide range of brightness level on the same picture, so it needs to decide what we want to keep, the brightest parts or the darkest areas.
Actually I prefer the camera to burn up the sky many cases instead to make the rest of the picture too dark, but if we don’t want that because it is not always beneficial we can use exposure compensation of -1/3 or -1/2 in very bright situations when we know we don’t want to burn up the sky or other bright part of the image.
The other option would be spot metering (see below) but it is not that easy, especially if we meter on something which is not 18% gray color, or we make an action shot which we cannot repeat, and we have short time to make a picture.
Or black bird against sky, here the bird will be really black without any detail, so we overexpose a bit.
To fully understand the matter, I explain metering a bit. For the camera properly meter we must focus on a 18% grey object. If we focus on a dark object, the image will be lighter, if we focus on a light object the image will be darker than expected.
There are different camera metering existing. First metering is when the camera measure light levels.
1. Evaluative / Matrix
I mostly use this, here the camera measures the whole frame, and in most cases it is reliable, just I use exposure compensation when needed. For properly use the camera lots of practice needed to know in different situations what kind of results expected.
I recommend to use this first, and when you familiar with it learn the others as well. Many photographer don’t use any other.
2. Center weighted
Here the camera calculates the center more than the rest of the frame
The camera only calculates the small portion in the center, or around the chosen focus point. Note not all cameras can measure around a chosen focus point, most cameras only measure in the center. With the spot metering it is the most easy to ruin the picture if we measure at the wrong place.
How to set and exposure compensation ?
On most Dslr cameras there is a button with +- signs and black and white color divided 45 degree. Normally must push the button first after turn one of the dial to set the compensation. Usually must hold the button while adjust the amount with the dial.
Most cameras today can set a value between +-5 EV. Some cameras only can set a value of +-2EV. No matter, apart from Night photography, in most cases +-1 Ev is the maximum value is needed.
On many compact cameras has not this setting, but some of them has I think. It is more likely in that case that exposure compensation can be found in the menu system.
Steps / increments
+ exposure compensation
Not many camera likes bigger (+2/3-+2) exposure compensation. What does it mean? We make a compensation +1 for example, we see the picture has no contrast, colors get different. My Canon camera (Canon 30D) for example much worse than my Nikon (Nikon D7000) in this regard. With a Nikon I can put +1 compensation without any problem, but the Canon struggles to keep the same quality. So check it if you like the results or not.
Exposure compensation effect on shutter speed
+1 EV (overexpose) means half shutter speed, for a lighter image more shutter speed is needed
-1 EV (underexpose) means double shutter speed, if we have not enough light we can cheat with it, meaning underexpose (- compensation) the images, to achieve good shutter speed and make it lighter in post processing, some cameras can push up as far as +6 EV, meaning we make a very dark images at -6EV and make it lighter in post processing, for this Raw / NEF image is needed.
Don’t forget to set back to zero after you don’t need it
When we don’t need this exposure compensation, we must set back to zero, because it can ruin our next photo, where the compensation is not needed.