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Blue Focus Adjustment

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Tip by Mr Bob:  An hdtv owner asked why the blue lines on the convergence grid is fatter than the red or green lines.  Mr Bob offers the following tip:

"If you can VERY CAREFULLY find the 3 Focus trimpots on the focus block -- be careful, they're backwards from what the service manual says, don't get the Screen trimpots instead, like another guy who had to pay me for a full, one-hour consultation to get back to normal--you can fine tune all 3 focusses, starting with the red, then the green, then the blue. On the block itself, find the labelling for Focus vs. Screen -- which you MUST NOT TOUCH, UNDER ANY CIRCUMSTANCES, the Screen trimpots -- by shining a flashlight onto the focus block from the side. R G and B will also be labelled on the focus block.

Focus red and green to be as tight as possible. Then very carefully go to the blue one.

Best focus will cause the blue to be dimmest. This will cause your whites to be dingy, yellowish, as lack of blue is yellow, on an RGB system.

Defocussing the blue trimpot just a little bit, with contrast at full or 80%, will restore the lost blue to your whites and cancel out the yellowish dinginess. Defocussing it too much will cause exactly what you're seeing now, the blooming.

This is all assuming the blue blooming problem is in your electrostatic focus and not your optical/mechanical focus, which could also be the problem. For that, see my entry on the Cantilever Technique.

The VE pluge pattern, with the 4 blocks stacked vertically, is the best pattern to use for this, concentrating just on the white block at the top of the 4 blocks.

Precision blue defocussing is reaching that happy medium between the dinginess and overdefocussing, where the blue blooms so much you can see it from your viewing distance, as it is doing now. When you reach that happy medium, you'll be there.

Then the white balance part of greyscale has to be checked to see if there's too much blue in the whites, but for now your eye will surely tell you that, after watching a few of your favorite DVD scenes. In doing a greyscale alignment, I always use my eyes only to set and check the white balance with various realtime video scenes, and my eyes also for the for the other levels of grey, with the Color Comparator coming into play only for double checking the other levels of grey, and how the white balance plays with the next highest level of grey, next to the full white.