Achieve the Exposure You Want, Part 2
In Part 1 of this series I explained why we might be interested in adjusting the exposure that our cameras are telling us is correct. I also explained that there is no such thing a “correct” exposure, but rather that each one of us might choose a different one depending on our artistic goal for the image.
So how do you change the exposure? There are many ways to do this, some of which are only possible with advanced P&S (point-and-shoot) or SLR (Single Lens Reflex) cameras. Because of this, I will only address the most simple and straight-forward method for now, and one that you should be able to use with even the most simple of cameras.
The easiest way of changing the exposure for a shot is using the exposure compensation function, normally called EV comp. (Exposure Value Compensation). If you own an advanced camera, there is likely a button on it that looks similar to the one pictured to the right of this text; just about every digital SLR should have one, although older film SLRs usually used other methods to achieve the same thing. If you have a P&S without the button, then you need to access this function via a menu; consult your camera manual to find out where to change the EV comp.
For now, all you need to know is that adding 1 stop of exposure (EV comp. of +1 stops, or simply EV +1) will double the amount of light reaching the film or sensor. Conversely, EV -1 will halve the amount of light. So, every stop doubles/halves the light, which implies that +1 is double (2x), +2 is double of double (quadruple, 2×2 = 4), +3 is double of double of double (octuple? 2x2x2 = 8), etc. With negative values like -1, -2 or -3 you would cut down the light by 1/2, 1/4 and 1/8, respectively. I hope this is clear!
Most cameras also allow fractions of a stop, in halves or thirds, so you can use EV +1.5 or EV -0.7, for example. Generally you can choose to have 1/2 stop or 1/3 stop increments, but not both. In general, 1/2 stops is precise enough for most people.
Following are some photos to exemplify when and how you would want to use EV comp.
This photo has a lot of white, which is always going to confuse your camera. Cameras always want to make white look like grey, and it’s your job to stop them! For the next photo I dialled in EV +1, so I made the image two times brighter than what the camera thought it should be; now it looks better (although maybe I should have used EV +1.5):
Correctly Exposed Photo
This scene has an almost equal mix of black and white, which average out and the camera produces (what I would consider) a correct exposure. No need to change anything here!
When you have a lot of dark colours in the scene, the camera will again try to make them look grey and the image will look too bright. To compensate for this you have to dial in a negative EV comp. to make it darker. As you can see in the above photo, the black camera isn’t really black. For the following photo I dialled in EV -1:
I would say the camera and lens look more like black now. Something some of you may notice is that the white lettering doesn’t look white anymore, and you’d be right. How to fix this will be the subject of another article, but for now I hope you’ve learnt why you need to keep that EV comp. button handy, and how to recognise when to use it. If you use a digital camera you will get the hang of it quickly as it’s easy to take a shot, look at the preview, dial in some EV comp., take another shot and then check out the result to see if you got the right value.
I plan to write an advanced version of this article in the future, where we’ll look at histograms, contrast curves, levels and other esoteric methods of achieving the exposure you want. But for now, happy EV comping!