Projector zoom allows you to increase or decrease the size of the projected image without moving the projector. Bigger zoom ratio provides more flexibility. The most common zoom ratio among today's projectors is 1.2. With a 1.2 zoom ratio you can vary the image size by 20% by simply adjusting the zoom lens.
Contrast ratio is the visual distance between the lightest and the darkest colour that may be reproduced on the display. A high contrast ratio is desired, resulting in richer dark colours and more distinctive color gradation.