Two weeks ago (forgive me for not posting this on time!), in our beginners guide to mastering a digital camera (aka: how to shoot in manual mode), we learned about aperture and shutter speed and the effects they have on pictures (if you haven’t read that article yet, you might want to check it out before going further.) Today, we’ll learn about exposure which is the most critical aspect of a good picture. Overexpose your image, and you’ll lose details in your subject’s face, underexpose the image and you end up with mottled skin and lackluster photographs.
All digital cameras have light meters, which are devices that detect the amount of light entering the camera. Some cameras will display this as a graph, others will display it as a number. Either way, the number zero indicates that the picture is properly exposed. Numbers higher than zero indicate over exposure (too bright) and numbers lower than zero indicate under exposure (too dark.) Supposedly, a properly exposed picture will always register at the “zero” mark. We’re going to work with this supposition for a while, and then I’ll explain the exceptions.
When shooting in manual mode, the aperture and shutter speed determine the exposure. To understand the relationship between these two, go outside on a nice day and set your camera to manual mode and your aperture to f/8. Point the camera at a flower or leaf and press down halfway on the shutter release button. The light meter will activate – look and see if your photo is over or underexposed (meter showing a number over “0”.) Without changing the aperture, change the shutter speed until the meter comes to zero. Now, without changing the shutter speed, change your aperture. Take the aperture up to f/11. Your meter should now be registering an underexposure. Take the aperture down to f/5 and your meter should be registering an overexposure. Can you see the relationship between shutter speed and aperture? To properly expose the picture, you can either take the aperture back up to f/8 OR you can take the shutter speed down until your meter registers zero again.
Aperture or Shutter Speed?
How do you know which one to change? That depends on what you’re taking a picture of. As we mentioned in the last post, if you’re taking a picture of a fast moving object, you want your shutter speed to be high enough to capture the action. Thus, you’ll set your shutters speed to what it needs to be (lets say 500), and the adjust your aperture to register a proper exposure. If, however, you’re taking a picture of a subject standing still and you want to blur the background, you’ll first set your aperture properly (lets say at 1.8 to get a nice blur) and then adjust your shutter speed to register a proper exposure.
Now, let’s say you’re inside on a cloudy day, and you’re taking a picture of your children playing. Because it’s dark in the house and you want to let in as much light as possible, you set your aperture as low as it will go and dial your shutter speed to register a proper exposure, but by the time the exposure finally reads “zero”, your shutter speed is all the way down to 10. This is too low to take a picture without blur, so what do you do?
This is where ISO comes in.
ISO is a rating system to tell how sensitive the image sensor is to the light present. The higher the ISO is, the more sensitive the sensor is to light. Take your ISO up, and your exposure will go up as well (likewise, take it down and your exposure will go down.) Now you can set your shutter speed to 100 to ensure there isn’t an image blur, and your aperture to the lowest available, and raise your ISO to the number it needs to be to register a proper exposure. As I mentioned previously, the higher the ISO is, the grainer your picture will be, so you don’t want to leave your ISO on a high number unless you have to, but when it’s the only way to get the picture, it’s a lifesaver.
Higher ISO: Grainer image, higher exposure and better low-light capabilities
Lower ISO: Less grainy image, lower exposure, crummy in low light situations.
Let’s take a look at our pictures with the golf balls again, and pay attention to the relationship between shutter speed, ISO, and aperture:
As the aperture number gets higher, the shutter speed gets lower. The higher the aperture number, the lower I took my shutter speed, until the point when I also had to raise my ISO in order to get a clear picture (I was pushing it at a shutter speed of 30 and REALLY pushing it at 13, but in both cases my arms were against the floor acting as a brace to avoid camera shake.)
When to over or under expose?
Supposedly, a proper exposure will register at the zero mark, but there are other factors involved. I’m trying hard not to bore everyone with way too much information, so I won’t go into metering and dynamic range in this article, but suffice it to say that your camera’s meter is not as smart as you are and it won’t always register a correct exposure. Use the meter as a guideline, take the picture, and then check your LCD screen. Is the image too dark? Too bright? Adjust the exposure accordingly.
Why does it matter?
This may seem like an awful lot of work, just to get a good picture, and it is – at first. But the more you practice, the easier it becomes until it’s pretty intuitive. But why go through all the trouble? Because you’re smarter than your camera! Consider this picture:
In order to keep from completely overexposing the background (although parts of the sky and bush are still too bright), my subject ended up way too dark. In manual mode, I can tell my camera exactly how I want the image exposed, and in this case I allowed the background to be over exposed, in order to properly expose what was important (the baby):
In the interest of full disclosure, I ended up with a composite, combining the two images to properly expose the baby and add back a little detail to the background…
Shooting in manual gives you tremendous power to get exactly the effects you want, whether it’s proper exposure or a blurred background or a fast capture of motion. It takes practice, but it’s well worth the time!
Put your camera in manual mode and start shooting!
If you have any questions, please don’t hesitate to email or leave a comment here and ask.
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