The Art Of Exposure Compensation | Internal Mechanics Of Camera Exposure.
Exposure compensation is a process by which we photographers are able to tell the camera what it should consider as the “correct exposure” and make adjustments accordingly. Our modern digital cameras are quite smart and they do get things right most of the time. However, there are certain problems still to be resolved. One of the most important problems is that our cameras cannot perceive what it is looking at. Yes, there are face- and eye-detection technologies available but their applicatios are very limited. Cameras generally tends to follow PRE-programmed algorithms for certain scenarios which can be problematic sometimes.
We will discuss the problem of exposure in this article. It is very important that you have a good understanding of light metering modes and its uses before you read this. All you need to know is right here:
Give them a quick read, they will help you a lot in understanding what we are about to discuss.
Let’s begin then:
The basic problem with our cameras is that it cannot differentiate between different subjects it views and tries to attain the same exposure for EVERYTHING. The camera just looks at the frame and depending on the intensities of the subjects, determines an exposure setting so that the ENTIRE FRAME is exposed for 18% grey. Think of 18% grey this way; if white is considered 100% light and black is considered 0% light, 18% grey is somewhat in the middle. This is what the camera ALWAYS aims for “correct exposure”.
I believe you would agree that absolute white snow and a dark black bear are not to be exposed the same way. The snow is supposed to look bright and white, while the black bear should look dark. Our cameras, however, do not understand this and hence the exposure problem.
When does this problem occur?
You may now wonder if the 18% grey formula is so outdated and archaic, why do camera manufacturers still use it? The reason is quite simple actually. The 18% grey rule DOES work most of the time. If you are a photographer who shoots average day-to-day life and not too much studio work, the rule does a wonderful job at exposing most of the pictures quite nicely.
The real problem however comes up while shooting extremely dark or extremely bright objects. For example, a snow-covered landscape or a black cat on a dark night. The basic problem that arises is the camera still tries to expose for the same 18% grey (no matter what it is shooting) and rounds up either underexposing the snow scene or overexposing the black cat.
Let me explain why….
As I discussed earlier, the camera cannot perceive what it is looking at. All it can “see” are various colors and their intensities. So when shooting the snow-covered landscape, the camera looks at the scene and finds it too bright, it tries to bring DOWN the brightness (since it is trying to expose EVERYTHING in the scene for 18% grey) by underexposing the image. Now the snow wouldn’t look white but a little grey.
It is the same deal with the cat. In the cat image, the exact opposite happens and the camera finds the black cat too dark and tries to bring it up to a grey undertone thereby OVEREXPOSING it. The cat too in this case would look a bit grey and not black as it should.
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Here is the solution:
Luckily for us, there is something that we can do. We can not only communicate to the camera that the desirable exposure is not what the camera is selecting for a particular scene, but also choose our own in the process. This method is called exposure compensation.
Now that you know exactly when these situations may occur when your camera light meter reading may be fooled and that may in-turn give you some wrong suggestions for exposure, let us jump in and learn exactly how you can fix it.
Fixing the exposure:
Before we learn more about the procedure to adjust exposure compensation, you must remember the following:
Exposure compensation can ONLY be adjusted while using Semi-Automatic Modes, i.e.
- Aperture Priority Or AV
- Shutter Priority Or TV
- Program Mode
The exposure compensation cannot be adjusted while using FULLY AUTOMATIC (God almighty, PLEASE for heaven’s sake get off that damn mode) or the FULLY Manual or ‘M’ mode. The reason is pretty obvious. While using the damn automatic mode you are letting the camera take all the decisions for you; so you are NOT allowed to make any changes. The opposite applies when you use the Manual mode, since now YOU are making all the decision and the camera is NOT allowed to override your settings, you have to decide how you want to adjust the exposure compensation. Changing the exposure compensation in manual mode has no effect.
How does exposure compensation work?
Let me explain what happens when you adjust the exposure compensation. Suppose you are shooting the snow -covered landscape in Aperture Priority Mode and the snow just comes out UNDEREXPOSED and grey. What you have to do now is dial down a few stops of exposure compensation (don’t worry I will explain later when to dial down and when to dial up).
Aperture Priority Mode lets you, as a photographer, set the aperture and in most cases the ISO. The camera in turn selects a suitable shutter speed that it thinks would expose the subject best. Now when you decide that the snow is getting UNDEREXPOSED and dial down the exposure compensation, the built-in light meter of the camera readjusts its scale for you. If you dial down the exposure by say 2 stops; what the camera does is determine the exposure that it thinks is correct for the image and then OVEREXPOSE it by two stops. I know this sounds very confusing but trust me you will get the hang of it very soon after you use it a few times. Read this paragraph one more time, you will need it. Try and remember the sequence.
Since you are using Aperture Priority Mode here, the camera can independently set its own shutter speed. The camera uses the shutter speed in this case to OVEREXPOSE the picture when you dial down the exposure compensation. Had you used say Shutter Priority, the camera would have then used the aperture to control and adjust the exposure. Now, if you think about it, it also makes sense why you cannot use the exposure compensation in FULLY automatic or full manual mode. It works only when the photographer shoots in conjunction with the camera and not independently on his own. Fascinating, isn’t it?
The tip-off though:
The images that you are trying to take may not always be a snowy landscape or a black cat, so how would you know if you need to adjust the exposure compensation on your camera?
Well here’s how…
The easiest and the most reliable way to check exposure and see if it is okay is to look at the histogram. NO, just looking at the LCD with your naked eyes is NOT good enough. The primary reason being that the LCD may look different in different scenarios like say under the sun, at night, if the LCD is not clean enough, variable brightness of the LCD and don’t even try to ascertain exposure if you are working with many cameras at the same time by just looking at the screen. The histogram is a MATHEMATICAL way of QUANTIFYING the data (about intensities of light) the camera just collected. In case you have not learnt anything in school, learn this…maths is hard but it is precise and accurate; so is the histogram.
Just ask yourself the following questions and you will be able to figure out if you need to use exposure compensation:
- Are there any subjects in your frame which are quite bright or quite dark?
- Take a shot and now look at the histogram. Does the histogram tend to gather up at the center
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If the answers to the questions above is yes, you need to adjust the exposure compensation. If you are shooting really bright or near white subjects; say a person with a fair complexion at the beach on a sunny day; the histogram should have a fair part of it accumulated at the right side of it since there is so many bright elements in the image. If, however, the histogram seems to have all in the middle and a very little at the far right side; it means that the camera has considered the bright elements as too much light and cut down the exposure to bring all down to match 18% grey exposure settings.
Rule of thumb:
A good rule of thumb to remember is to look for the details. Nowadays if you are shooting RAW and are off by a stop or two you can fix it in post-production but anything more than that maybe irrecoverable. What you should always be looking for when you are shooting are the details. Just after you take a shot, zoom in and check if the details are visible; especially if the subjects are too bright or dark. See if the weave patterns of a black cotton shirt is visible or if you could make out the feather textures of a white swan. If however the shirt appears to be a giant black blob, double check the histogram like I asked you to; you may have an exposure compensation issue here.
I did NOT discuss how to adjust your exposure compensation intentionally since it varies widely from camera to camera. In some cameras you have to change it through menus and in others, there are dedicated buttons which you can press and then use a dial to adjust it. Please consult your camera manual for this.
Always remember there is NO such thing as “CORRECT EXPOSURE”. It all comes down to what YOU, the photographer wants. You may want a high key photograph that is nearly all white or vice versa.
The camera may wildly disagree with you on that but that doesn’t matter. You are the decider, the decision maker. The camera is just a tool which you use to bring your visualizations to life. So if you think that the camera is not exposing how you would like to have, tell it what to do. Because now you know how.
A little algorithm to remember easy:
Bright Subject -> Camera Underexposing -> Dial DOWN exposure compensation.
Dark Subject -> Camera Overexposing -> Dial UP exposure compensation.
Hope you found this topic helpful. I know it is a little hard to grasp all of it in one go. I suggest now that you have read the article; find scenarios where you may need to adjust the exposure compensation and then use it. After you use it a few times, re-read this article one more time and you will be all set.
So, go out there and shoot….now, now, now!
Also published on Medium.