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Image Appearance

The interplay between the scene, the lens and the image sensor is demonstrated in Figure 13. The sliders at the bottom allow you to control the positions of the object (car), the image sensor, and the aperture size. By moving the image sensor back and forth, you can see the car and the building go in and out of focus in the captured image. For any chosen position of the image sensor, the vertical dotted line shows where an object must be for it to be in focus. Moving the car towards the dotted line will bring it into focus. Hence, you can get a sharp image of an object by either moving the image sensor, or the object, or both.

Car Position Sensor Position Aperture Size

Figure 13: Image formation

Use the third slider to control the size of the aperture. As expected, a larger aperture makes the image brighter. However, a larger aperture also makes the non-focused parts of the image more blurry, while a smaller aperture increases the overall sharpness of the image. Reducing the aperture to a tiny hole will turn the lens into a pinhole. As we know, a pinhole camera produces an image without any blur, but it is an extremely dim image.

Let's summarize the process of taking a photo. The lens captures the light from the scene and forms an image on the image sensor. You adjust the relative distance between the lens and the sensor until the object you are interested in is in focus. You then increase or reduce the aperture size to adjust the brightness of the image. With these choices made, you are ready to "shoot" your photo.