A zenith telescope is only able to look straight up. This means that it can use a mirror which is a smoothly spinning pan filled with liquid mercury. The LZT uses 28 litres of mercury, spinning once every 8.5 seconds. This type of mirror can be made much larger and cheaper than a conventional mirror, which means it collects much more light. This light is focused into a CCD to make an image. The LZT is used for "transit imaging". This means that earth's rotation moves stars past the telescope. Images can be taken by moving the sensor electronically in step with this movement.