Saturday, 23 March 2013

Why are there stars?

For anyone who can remember the old projector at Lollipop, you will probably also remember what has lovingly been referred to as the "startfield" which appeared in the conference room. This pattern of a mixture of flickering and static white dots were, as you might have already guessed, dead pixels. Or more accurately stuck pixels.

Our DLP projector uses an array of tiny mirrors to reflect light at just the right time as each color filter on a spinning wheel moves in front of the lamp to produce a recognizable image. These mirrors are stuck, reflecting the light constantly. Why? My guess is that since the projector sat so low and at an angle on the conference table that it needed the keystone to be highly adjusted to make it seem straight. This cut off a large section of the DMD and these mirrors were kept off, I think they just got tired out.

So, where did these stars come from exactly? Well I tore down the projector and got an "inside look."
Here are some images of the DMD:

Here we see the tell-tale "burn" of where the keystone was focused.

A closer version with outlines highlight the keystone "burn." A blue line shows where the Macintosh menu bar has left its print.
And here, the origin of our star field.

"All that glitters is not gold." It's true, it's aluminum.