NotTaR of Television Sets : Blue focus different for projection sets..  
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Blue focus different for projection sets?

On some 3-tube projection sets, you may find the blue tube to have poorer focus than red and green. Don't touch it!

(From: Dakuhajda (dakuhajda@aol.com).)

What you are describing is completely normal. The manufactures design in the blue picture tube so that it will not focus completely.

In fact the service literature lists exactly how much and which way it should be out of focus. In fact the picture generally looks better with the blue CRT slightly out of focus per specification - slightly wider than the scan lines so that it completely fills in the scan lines. The slight out of focus is designed to blend in the scan lines so they are not as noticeable on the big screen.

This is because when the standard TV signal with 262.5 lines being displayed at any given time, it looks bad to see the scan lines. The standard TV signal was never designed to be viewed on a screen larger than 25".

It also is the nature of the phosphor that makes blue not to allow a good focus. Especially in the older sets. I have not seen any early blue projection tubes focus well even when they were new.