IAC DISCUSSION FORUMS

Not a major issue ... but every video projector I know has a lens cap.

The catch is that the lens cap fits onto a lens which usually has a very free-moving focus adjustment. Thus there is a risk of spoiling focus every time you take the cap off or put it on. In a domestic setting that may mean some fiddling to re-focus each time ... and if the machine is mounted on the ceiling of your lounge or home-cinema it is even more of a pain.

Are they essential? What happens to those machines mounted in the ceilings of halls and cinemas?

I have had a video projector mounted on the ceiling for five years WITHOUT a lens cap The picture is still clear and clean. Should dust accumalate on the lens I would just climb a step lafdder and use a dust blower. In any event I have refocused now and then with the remote with no problem. Perhaps I am lucky.

While lens caps do serve a dust reduction function, I've always thought that their main purpose was to protect the lens from impact damage during storage or transport. But if your projector is permanently set up there isn't really much need for them, ceiling mounted projectors are quite common in conference centres and meeting rooms and none of them are likely to have lens caps on. So I guess dust isn't really a problem and the lenses are only cleaned when someone makes a complaint or when they have to change the bulb.
If the projector is nearer ground level and you're concerned about dust I think a dust cover over the whole projector would be more practical than just a lens cover and it removing it won't upset the focus.