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Image FormationWhen light from an object passes through a lens, it converges towards a single point and is said to be focused at that point. If an object is at a distance o from a lens of focal length f, the light from that object will converge at a distance i from the lens on the other side. The relationship between these two distances is given by the Thin Lens Law [1]:
To observe an image of an object, a flat surface (or plane) must be placed behind the lens so that the light from that object can be captured. Placing the plane where the object's light is focused will produce a sharp, focused image of that object. There is a challenge, however. If the person in Figure 7 was in a different spot, the imaging plane would also need to be in a different spot to keep him or her in focus. Moreover, if two people stood in different spots in Figure 7, only one of them could be perfectly in focus on the imaging plane. Figure 8 demonstrates this situation. By moving the imaging plane, the car and the building move in and out of focus in the captured image. The red area on the imaging plane corresponds to the single red point of the car. The car is blurrier when the red area is larger. The vertical dotted line in Figure 8 shows where an object must be for it to be in focus. Moving the car towards the dotted line, then, will bring it into focus.
Figure 8 also shows the len's aperture, which is the unblocked portion of the lens. Making the aperture small will let just a small amount of light pass through, but the image will be more focused since the light will not spread out as much [2]. Making the aperture really small will change the lens into a virtual pinhole.
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