CurtPalme.com Home Theater Forum

[garyfritz]

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Here is an explanation of why it is/was common to defocus the blue CRT: your eye can't focus on the blue details anyway! So we defocused the blue to get more light output (electrons hitting more phosphor area) from the the easily-burned blue phosphor. Nobody noticed it, except maybe a blue fringe around white titles on black background.

https://calebkruse.com/10-projects/seeing-blue/

When I was a kid I always wondered why red and green Christmas lights looked normal, but blue lights were always a blur... now I know!

[kal]

Cool!

Years ago when first calibrating my Zenith 1200 (CRT projector) having to *completely* defocus blue to keep they greyscale correct without having to lower the light output to unacceptable levels. I remember looking at the lines on a blue grid pattern that were about 5x wider than red or green, and completely fuzzy, thinking "no way this won't be noticeable on actual content". But it wasn't, at all. Watched thousands of hours of content that way.

I remember there was only one time it was noticeable: I don't remember what movie, but it was one that had the scrolling credits at end entirely in blue for some odd reason (I looked in the tube faces and the red and green were completely off). Couldn't read any of text on the screen at all.

Ka

[kal]

Cool!

Years ago when first calibrating my Zenith 1200 (CRT projector) having to *completely* defocus blue to keep they greyscale correct without having to lower the light output to unacceptable levels. I remember looking at the lines on a blue grid pattern that were about 5x wider than red or green, and completely fuzzy, thinking "no way this won't be noticeable on actual content". But it wasn't, at all. Watched thousands of hours of content that way.

I remember there was only one time it was noticeable: I don't remember what movie, but it was one that had the scrolling credits at end entirely in blue for some odd reason (I looked in the tube faces and the red and green were completely off). Couldn't read any of text on the screen at all.

Ka

[Dancrt]

Yeah interesting 🤔 article
My d50 blue couldn’t get sharp the barco 909 you can and the blues on the d50
Where not very blue where the 909 can do Aweosme blues I assume they use different phosphor?

[r.bauer]

That's why I have a pair of glasses made for calibrating the blue CRT. It is a pair of glasses for looking in the distance (so no reading glasses) and the strenth is -0.5. No one with their right mind would even consider buying a pair of glasses if they have such a small amount of correction needed. But with this pair of glasses on my nose I can see blue clearly! Something that is normally not possible as explained in the link. This all applies when tou have normal, healthy eyes and don't (need to) wear glasses.

This in turn allows you to also otimally adjust, focus, astig, etc. to have the blue tube in the best possible starting situation for setting the greyscale. Now if you de-focus blue in order to get more light output, you now know you have the maximum adjustment range when starting this procedure.

Also geometry and convergence can be set a lot better, this means that (taking drift into account) you will have a better picture as the projector warms up.

I thought I already posted something on this topic overhere, as I discovered this long, long time ago and also shared this where ever possible.

The reason why Blue was defocussed was mainly because the blue tube just couldn't put out enough light without defocus the electron beam. As luck will have it, we humans can not focus on blue so there ws only a small price to pay. Other fosfors just weren't available.

[kal]

That's a pretty cool idea r.bauer!

Kal

[kal]

That's a pretty cool idea r.bauer!

Kal

[km987654]

[bachiano]

I painted my man cave a very Dark Blue 20 years ago for the same reason. It worked very well.