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Getting to grips with exposure is an issue for most amateur photographer and newbies yet so easily understood. By grasping a few simple principles you are on your way to great images. A great image needs perfect exposure and so in order to get that perfect exposure you need to take note of just three factors.
Exposure to me for years was a mystery. Post why? Because I did not take the time and effort to understand it. When I did I was able to shoot great images every time I pressed the shutter button.
1. Aperture
This was always a mystery to me and the fact that 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 large 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 will cause you to overexpose your image and too little light will underexpose it and 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 will not 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 and allowing just the right amount of time 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.
3. Relationship between aperture and shutter speed
Depending on how bright the light conditions you are photographing 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, f2.8, 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, ie 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 the 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 f4 to f8 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 f4 aperture and 1 / 250th of a second shutter speed then by changing your aperture by half you need to double the time to only 1 / 125th 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 or aperture value or Tv which means time value. Each of these gives priority to either aperture or shutter speed. So lets say you decide for creative reasons to use Av and that you want an aperture of f2.8. 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 is not 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.
By understanding how these settings work you will always get that perfect exposure every time. Happy shooting!
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Source by Wayne G Turner
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