The Optics Book -

The Optics Book - Optics Instruments

Karen

English

chino

Photocopy Machine

Most of the times that you use a photocopy machine, it is to make an exact copy of a page. By exact copy, I mean preserving the same size font or image as the original. A photocopy machine basically involves placing an original onto the glass, under which there is a lens, and under the lens there is a paper onto which the copy will be made. The object (which is the original) is projected onto the screen (which is a piece of paper).

Under most circumstances, the photocopy machine will involve a Case 3 situation. This is where the object is at 2F, and the image formed will be the same size, real and inverted, on the other side of the lens at 2F. Although the image is inverted, it doesn’t usually matter, because you can just turn the paper to the correct position.

Sometimes, if there is a small part of a picture that you want to photocopy, you will enlarge the image so that it will be large enough to take up the entire page. This would involve a Case 4 situation, in which the object is between F and 2F, and the image is magnified, still real and inverted, on the other side of the lens, and beyond 2F. We know that the photocopy machine itself does not change size. Therefore, something inside of the machine itself must be moving. This is the lens itself. To enlarge an object, the lens will move towards the glass upon which the original is placed. This way, the object will be between F and 2F, and at the same time, the distance to where the paper on the other side of the lens is placed will be increased so that the image will be beyond 2F.

At other times, you might want to minimize the image. When this happens, we switch to a Case 2 situation, where the object is beyond 2F, and the image is between F and 2F on the other side of the lens, and the image is smaller. This time, the lens is moving closer to the paper upon which the image will be formed. This will increase the distance between the glass and the lens, and decrease the distance between the lens and the paper.