14 Jul Basics of dslr photography what is Exposure
Basics of Photography
is the final post in the Basics of Photography series. Please check the previous 2 post about aperture and Shutter speed. In this post we will discuss Exposure and how you can combine both aperture and shutter speed to achieve the correct exposure while capturing your image.
Above image is a courtesy www.slrphotographyguide.com
Exposure is the amount of light per unit area hitting the film or the sensor depending on the shutter speed, aperture and ISO. As seen above, a picture can be over-exposed , under exposed and correctly exposed. Over-exposed image look bright and washed out and under-exposed image look dark.
If your camera is showing the below settings in the exposure scale then the current exposure settings will capture a overexposed image.
Above image is a courtesy www.naturephotographysimplified.com and shows the settings when the scene is over exposed. Here the shutter speed it 2 seconds and aperture is f2.8. If we want to keep the same aperture and get the correct exposure we need to change the shutter speed by 3 stops to 1/4th of a second.
Both aperture and shutter speed can be increased or decreased in terms of stops. 1 stop increase means doubling the current value and 1 stop decrease means dividing the current value in half. So in our example above 3 stops decrease means 2″, 1″, 1/2th and 1/4th. If you get this basics correct you have understood the basics right.
Image of the scale when a scene is under exposed
Above image is a courtesy www.naturephotographysimplified.com and shows the settings when the scene is under exposed. Now here also we are keeping the aperture at f2.8 and changing the shutter speed to get the image correctly exposed. The shutter speed is reduced by 3 stops again 1/30s,1/15s,1/8s and 1/4s to get the correct exposure.
In both the above example we kept the aperture constant at f2.8. But the image could have been correctly exposed by changing the aperture as well. Lets say in the first example where the image was over exposed by 3 stops we want to keep the shutter speed at 2 seconds and change the aperture then the aperture would be increased by 3 stops since that will cut the light coming in by 3 stops and image will become correctly exposed. So the aperture in that case would be f2.8->f2.0->f1.8->f1.4.
I will let you figure out the correct aperture setting for the second example if we wan the shutter speed to 1/30th of second.
For more tutorials about perfect exposure check the following references.
Camera Exposure from Cambridgeincolour.com
Photography Exposure Basics by Richard Schneider at PictureCorrect.com Website
The Exposure Triangle techradar.com Website