dirt is covering the screen. At the upper left corner it is more prominent. It seems that this effect is not real dust, but electronically generated one way or another. Although I have experience repairing electronic equipment, due to the lack of a repair & maintenance manual I feel diving in shallow water
Office Equipment & Supplies - InFocus - Proxima Pro AV 9310 Multimedia Projector
Answers & Comments
Thank you for posting your question on fixya. This problem can be due to a mis-aligned lens. The lens is located next to the lamp unit and see if adjusting it will resolve the issue. If it doesn't then I suspect one or more of the 3 LCD panels(red, blue and green) require service. This is not a user serviceable repair and I strongly advice that you get professional assistance to get it done.
Let me know if you have any further questions,
Sai.