Metering and exposure are tough companions. Although they seem to work well together on the surface, metering may trick you into exposing poorly. Here are some experiments showing you how to take control of exposure and use it creatively, especially in aperture priority mode.
There is a lot of nonsense written about camera exposure modes. I roll my eyes when I hear people have to use manual mode. It’s completely poppycock. Understanding how manual mode works is one thing. However, being told you have to use it is another.
I love aperture priority. It does a lot of heavy lifting for photographers. Its big advantage is that the camera will expose the image according to the measurement. The equally important downside is also that the camera will automatically expose based on the metering. Let me explain.
If you don’t know, this mode allows the photographer to set the aperture and the camera automatically adjusts the shutter speed. Turning the mode dial around A (Av on a Canon) gives the photographer quick control over camera settings.
When shooting events such as weddings, I invariably use aperture priority. Why? Due to ever-changing lighting conditions and how quickly the camera compensates for this. It can go from 1/60th of a second to 1/2,000th much faster than I can turn a dial in manual mode.
Also, the camera imposes restrictions on exposure settings that aren’t there in shutter priority or manual mode, making it much less likely that I’ll accidentally take an incorrect exposure. “What,” I hear you gasp, “can an experienced professional photographer make a mistake?” You better believe it, and it can happen to anyone. Admittedly, the risk of doing so has diminished since the switch to mirrorless; I can see both the histogram and a close representation of the final image through the viewfinder before pressing the shutter button. Despite this aid, exposure is limited by both the widest and the smallest apertures. I can set the aperture to either extreme and still get the right exposure.
Plus, aperture priority is a great way to learn the counter-intuitive way metering and exposure work together. That’s why I use it for the following experiments.
With your camera set to ISO 100 (200 if using Micro Four Thirds), in aperture priority, take test shots at the widest and narrowest apertures in a dimly lit room. On a standard kit lens, this might be something like f/3.5 and f/22, respectively. The exposure will be the same at each extreme, although you may find it difficult to hold the camera at the narrowest apertures because the shutter is open too long.
Now do the same thing in shutter priority. At one extreme, the image will be pure white and at the other, very dark. The correct exposure will cover an area somewhere between the two extremes.
In shutter priority, the camera is limited by the longest and shortest shutter speeds. This range is 60 seconds to 1/32000 second on my camera, although yours may differ from this one. Thus, it makes it possible to accidentally and catastrophically overexpose or underexpose your photos.
Then, indoors, set your camera to take a properly exposed photo in manual mode. Then step outside into daylight. How long does it take to adjust the settings to get the right exposure? Try again in aperture priority. Now the correct exposure should be acquired instantly.
There is, however, a problem to overcome with this approach. Metering may cause the camera to expose incorrectly.
Your camera expects the world – on average – to be a particular brightness. The sky is clear, the ground is darker, and there is a mixture of tones in between. This is a simplified explanation, but on average he thinks the world is medium in color, often referred to as medium gray or 18% gray.
Make sure your camera is set to its full frame metering mode. This is called matrix, multi, multiple, multi-segment, multi-pattern, evaluative, or ESP, depending on your camera brand.
In aperture priority mode, take a picture of a common outdoor scene, such as a park or a tree-lined street. The image should expose correctly. Now fill the frame with something white, like a sheet of paper. You may need to draw an X on it first so the camera can focus. Look at the photo on your back screen. It will appear gray. Your camera has been misled by all that whiteness. He expected the frame to be a medium color and not pure white, so he reduced the exposure accordingly.
To override metering, you need to add positive exposure compensation to brighten the image. This may require pressing a button marked +/- and turning the main dial, called the command dial on some cameras. Alternatively, if your camera has a second dial, turn it clockwise. You should see an indicator in the viewfinder indicating that the exposure is increasing. Turn it to about +1.7 and photograph the piece of paper again. It should not appear white. The precise amount of exposure compensation may vary from camera to camera.
What does this mean in the real world? If you are shooting a very bright scene, such as snow, sunny sea or bright sand, you should add positive exposure compensation to brighten the image, otherwise the camera will make it too dark. It may seem counter-intuitive to brighten a photo of a bright scene, but it’s what you need to do. I apply exposure compensation to almost every photo I take, which is why I only buy cameras with two dials.
The exact opposite is true of shooting something black. Reset the exposure compensation to zero and fill the frame with something completely black, like the back of a camera bag. Look at the picture. Again, it looks gray and not black. This time you need to dial in negative exposure compensation. Try -1.7. So if you’re shooting in a dark room and you want to show that darkness in a photo, then you have to dial in negative exposure compensation to make all those shadows dark.
You can use underexposure and overexposure creatively. In a dimly lit room, use a bright light to illuminate a subject. Or, if you’re outdoors, look for rays of sunlight shining through the shade of trees or buildings. Dial in even more underexposure until the shadows turn black and the very bright highlights are in the midtones.
Now look for a very bright scene with a dark element. Dial in the overexposure until the scene becomes almost white and the dark element moves into the midtones.
Camera sensors allow variable leeway to correct exposure errors. If your camera has messed up a bit and especially if you’re shooting raw, you can usually correct it in post-processing, although it’s always best to try to get it right in camera. However, if you push it too far, you’ll lose detail and risk introducing noise when brightening a shot. Therefore, it’s good to know how far you can push exposure in either direction and still get good results. Try shooting a scene several times. Increase and decrease exposure. How far can you push it in either direction and still get acceptable results in treatment?
This article only scratches the surface of exposition, and there is a lot more than what I have included in this short article. Feel free to post your test results in the comments. Do not hesitate to ask your questions there. Plus, Fstoppers has a fabulous course that will help you learn about other aspects of exposure and essential camera techniques. Many writers here also host hands-on workshops, and it’s worth checking to see if there’s one in your vicinity.