So as we have already learnt, if you have a slow shutter speed, the images will be blurred. If you have a fast shutter speed the images will be a crisp and sharp. Now, there is a problem. If you make the shutter speed too fast, so that the “image sensor” is open for only a fraction of a second, very little light from the image will reach the image sensor. If this happens, the image will be dark!
What if you want to capture a airplane that is moving fast without letting the picture become blurred or dark? To achieve this, you will have to use the “aperture”!
Simply put, the aperture is the hole though which the light from outside the camera goes inside the camera and to the image sensor. So, if you have a big aperture, you will have more light coming in. If more light comes in on the image-sensor, the image will be brighter. On the other hand, if the aperture is small, less light will come in to the camera and on the image sensing element! This will make the image darker.
So, how do you take a picture of an airplane that is flying by you without making the image go blurred or dark? First you need to have a high shutter speed. With this, the image sensor will be exposed for only a fraction of a second. This will make sure that the image is not blurred. Now, as we know, if the shutter speed is too fast, not enough light will reach the image sensor, so the image will be dark. So, to overcome this, you need to make the aperture size large! If you do both these settings right, you will have a perfectly clear and bright image.
However, when you make the aperture size big or small, another interesting thing also happens. This interesting thing is called “depth of field”!
If you look at the first
image, the leaves
are sharp and clear, the mountains are blurred out completely. If you
look at the second image, the glass is also clear. The background is
also clear. Everything is clear. This is basically what depth of field
is all about.
The fist image has a small
depth of field.
So the objects that are close-by are clear, the objects that are far
away are not. The second image has a large depth of field. So the
objects that are close as well as far are clear.
So, how do you use this “depth of field” concept. Why would you need this? So that you can convey a message though your image. How? Imagine this…there is a couple that is standing in front of a busy street. You want to take a picture of this happy couple. You also want to subtly convey, that the couple is happy in their own world. Their happiness is not affected by the rest of the world. If you want to convey this, would it not be good if you can have the couple sharp and clear but the whole background subtly blurred and faded away!
This is just one example. You need to be creative and come up with your own ways to use this method of blurring what you want and keeping what you want sharp. The general understanding is that, you keep what ever you want the viewer to focus on sharp. You can blur out everything else.
So, now the question is, how is “depth of field” related to the aperture? Simple, if the aperture is large, only near objects will be sharp everything else will be faded away. If the aperture is small, everything will be sharp. So, it’s inversely proportional.
If you want to take the picture of the couple, what should your aperture be, large or small? Large. If it large, then only nearby objects will be clear everything else will be blurred.
If you want the whole picture and the background and everything clear, what should the aperture be? Small!
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