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.

EV (exposure) compensation buttonThe 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.

Underexposed Photo

What the camera thinks is correct exposure

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):

What I think is correct exposure
Correctly Exposed Photo

A correct exposure, hooray!
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!

Overexposed Photo

What the camera thinks is correct exposure
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:

What I think is correct exposure
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!


10 Responses to “Achieve the Exposure You Want, Part 2”

  1. Yay for sticking with new year’s resolution #4!

    Possibly worth mentioning that many older cameras (Pentax M and A series included) had whole-stop EV comp, indicated as 4x (+2EV), 2x, (+1EV), 1x (+0EV), 1/2x (-1EV), and 1/4x (-2EV). I thought this was a little odd the first time I held one of these bodies.

    • That is a good point, Andrew. I’m simply assuming that those who will find this introductory article useful will not be shooting a 20-year old mechanical SLR, but rather a modern SLR, or more likely a digital SLR or P&S ๐Ÿ™‚

  2. Mis, since this is an introductory article I think it’s worth pointing out that the exposure compensation function may not be available in fully automatic (green) mode, or in “scene” modes…

    For example, this is the case with my Canon 350D (Rebel XT).

  3. Oh, and on many cameras the EV setting is a “sticky” one. If you use it, don’t forget to check it, and change it back to “0” if you don’t need it for the next shot…

    And don’t forget that the camera may remember the last-used EV setting, even if the power is turned off… ๐Ÿ™‚

  4. Good point Paul ! The EV is definetly sticky on my “dinosaur” film slrs. Many times have I forgot to change it to 0 ๐Ÿ˜€
    And good post Mis ! Once EV’s are learnt and all that one can have a lot of fun experimenting !

  5. OK, but exposure isn’t a purely independent variable: it’s the product of the aperture/shutter speed/iso combination–right? So you still have to (or should I say, “can”) tell the camera which of those variables it can adjust to achieve the EV you’ve specified.

    • Dadipentak, I tried keeping this article as simple and basic as possible. Of course, you can shoot in M mode and vary aperture or shutter speed (or ISO, if shooting digital) manually to achieve the exposure compensation you want, or shoot in Av so the camera changes the shutter speed, or Tv so it changes the aperture. But again, I wanted it reaaaaally simple. There will be more opportunities to complicate things.

  6. Sorry–it’s hard to think of myself as being advanced but I’ll take this as evidence that I’ve actually made some progress in the past year ;~)

  7. Sune /Jonson PL Says:

    This is a great article on something that can easily be confusing.

    “Something some of you may notice is that the white lettering doesnโ€™t look white anymore, and youโ€™d be right. How to fix this will be the subject of another article”
    Let us know, when you’ve written this next article related. (Maybe with a link at the bottom here)

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