Getting to grips with exposure is an issue for most amateur photographers and newbies. By grasping a few simple principles, you are on your way to great images. A great image needs perfect exposure, and in order to get that perfect exposure, you need to take note of a few factors.
“50 50 50 50 50” captured by Thomas Hawk (Click Image to See More From Thomas Hawk)
Exposure was a mystery to me for years. Why? Because I didn’t take the time and effort to understand it. When I finally did, I was able to shoot great images every time I pressed the shutter button.
1. Aperture
This was always a mystery to me—the small aperture numbers and the aperture size always seemed to be the opposite. Let’s simplify it. Aperture determines the quantity of light that you allow to reach the sensor or film. Liken it to a tap. Open the tap wide open and a large quantity of water comes out. Open it up just a little and a small quantity comes out. So when you open up your aperture wide a l,arge amount of light hits the film or sensor. The ability to control the light is essential to achieving perfect exposure.
The size of the aperture affects the depth of field, but we’ll look into that in another article. There is another problem; too much light causes you to overexpose your image, and too little light will underexpose it; the image will be too dark. So now you need to find a way to control how much light reaches the sensor. Let’s go back to the water illustration. Equate the perfect image to a bucket of water. Too much and the water will overflow and too little will result in a half full bucket. So now you need to control the time the tap remains open. That takes us on to point two.
2. Shutter speed
Voila! The answer to your problem is shutter speed. This equates to how long you allow the tap to remain open. If you leave the tap on for a long time, the bucket will overflow and for too short a time won’t give you a full bucket. So what do you do? You have to find the perfect time that will let in enough water to fill the bucket. By getting your timing right you will get the perfect image. But wait, something is not right. There are so many shutter speeds and apertures. How do you get them all right? Let’s take a look at the relationship between aperture and shutter speed.
Photo captured by John Mills (Click Image to See More From John Mills)
3. Relationship between aperture and shutter speed
The light conditions you are photographing in will determine how much light needs to reach the sensor to create a perfect exposure. If, for example, you have your aperture set to wide open on say, f/2.8, then you are allowing in a large quantity of light. The bucket will fill quickly so the tap can only be open for a short time, i.e. you will set a very fast shutter speed. As you close down and make it smaller so you will need to increase your shutter speed or leave the tap on for longer until your tap is just dripping. This will mean in order to get a full bucket the tap will have to be left on for a very long time.
Aperture and shutter speed affect each other. Change one and you’ll need to change the other. Each setting halves or doubles the amount of light each time your change it. By going from f/4 to f/8, you halve the amount of light reaching the sensor and so on as you move to the next aperture number. So if your perfect combination is f/4 aperture and 1/250 of a second shutter speed, then by changing your aperture by half you need to double the time to only 1/125 of a second. The nice thing about digital cameras is that they do this for you automatically.
4. Exposure settings
There are two settings you need to concern yourself with. Av (aperture value) or Tv (time value). Each of these gives priority to either aperture or shutter speed. So let’s say you decide, for creative reasons, to use Av and that you want an aperture of f/2.8. How do you know what shutter speed to use? Voila! The camera chooses the shutter speed for you. The same goes for Tv or shutter priority. You choose the shutter speed and the camera automatically sets the aperture for you. Simple, isn’t it?
The reason why you would want to choose the aperture or shutter speed are for creative reasons. A large aperture blurs out the background and creates what we call a narrow depth of field or focus. A fast shutter speed may be necessary when you shoot action photos and want the subject sharp and not blurred by the speed.
“Me in HDR Again” captured by Great Salt Lake Photographer (Click Image to See More From This Photographer)
By understanding how these settings work, you will always get that perfect exposure every time. Happy shooting!
About the Author:
Wayne Turner has been teaching photography for 25 years and has written three books on photography. He has produced 21 Steps to Perfect Photos; a program of learner-based training using outcomes based education.
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got some basic education here. thanks.
Wow, that is a great way to explaing the relationship between the two. It took me a long time to understand components of exposure. I wish I would have heard it explained that way soon. It would have been so much easier to understand. Thanks for sharing!