BenQ BX4004D is a DLP projector for educational use. It features Dust-proof and short focus. In order to adapt to the harsh dust environment, BX4004D uses hill filter to prevent dust invasion. The revolutionary improvement of filter screen and wind path, dustproof performance are strong, highly reducing the damage caused by dust on the fuselage. At the same time, the long-acting bulb life can save later maintenance costs.