Film-Tech Forum ARCHIVE: Why is Convergence Important on CRT projection TV's

This is topic Why is Convergence Important on CRT projection TV's in forum The Afterlife at Film-Tech Forum ARCHIVE.

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Posted by Lyle Romer (Member # 1266) on 12-30-2008, 12:23 PM:

OK, here is something I've been thinking about. Why is it that on a CRT (and I'm assuming 3-chip DLP) projector, convergence of the three colors is very important but........

In an LCD or Plasma display (or even large LED display), each "pixel" is really a red, green and blue pixel next to each other. I guess in this case, our eyes are really seeing 3 completely separate images and integrating them into one full color image.

So that brings me back to my CRT/DLP question. How come if the convergence is off, we can see it when we can't on other types of displays.

Posted by John Hawkinson (Member # 1135) on 12-30-2008, 01:24 PM:

Ignorant hypothesis: what we perceive as "bad convergence" on a CRT is substantially larger linear distance than the inter-subpixel distance on an LCD?

--jhawk

Posted by Mark Ogden (Member # 43) on 12-30-2008, 02:10 PM:

John is right, because in solid-state display devices, the convergence is never really "off", as after the manufacturing step nothing is ever converged. That is to say, the red, green and blue pixels, be they lcds, plasma capsules or micro-mirrors, are permanently fixed in position in a very small area relative to each other, nothing is variable in the way they illuminate save for the actual input signal, and the apparent "convergence" never changes. In DLP devices that operate with separate R G and B micro-mirror arrays, they are precisely aligned at the factory and then permanently fixed in position.

Posted by Mark Ogden (Member # 43) on 12-30-2008, 02:17 PM:

Whoops, double post . .