CurtPalme.com Home Theater Forum

[gregstv]

Hi Guys,
I had a brain fart about blue defocusing to get the correct gray scale tracking.
Digital projectors use a polarizer to intensify the blue light to get good white balance. I was thinking if the blue coolant was tinted you wouldn't need as much blue defocus. Has anyone ever tried tinting the blue coolant with blue dye?

[gjaky]

With blue dye you can only (fine)tune the spectra of the light. The purpose of blue defocus is to get more blue output the two are not the same.

[gregstv]

Thanks,
I am doing the red and green and thought I would have a go at the blue. Sounds like its probably not worth it.
Greg.

[gjaky]

In fact it would make the thing worse. With color filtering you actually loose light output, so adding a blue filter would cut blue output even further. On the other hand blue filtering is not even needed because the primary clolor coordinates of the blue phosphor are spot on according to REC.709 color space.

[Nashou66]

[gjaky]

Nashou, I think he has SEOS 808s units with AC lenses.

[garyfritz]

Yeah, the purpose of dye (or colored C-elements or whatever) is to adjust the spectrum. The phosphor doesn't match the correct CIE coordinates for Red & Green so the filtering shifts it a bit and improves the color accuracy. Blue phosphor is already really close to the correct CIE value so you don't need to filter blue. See e.g. my post on Calcolor filters.

And you also don't WANT to filter blue, because blue phosphor doesn't produce enough light already. The purpose of the blue defocus is to get more light out of the tube. If you have a sharply-focused blue, that small dot of phosphor can't produce enough light, and your color balance is off. If you smear the focus a bit (electrical focus, not optical), that small dot now covers a larger area. More area = more phosphor = more light, so that helps to boost the blue level for proper color balance. Fortunately your eye can't focus very well on blue, so you don't notice the defocused blue unless you look at something like white text on a black background. See e.g. this post and this post if you want lots more explanation.

[gregstv]

Thanks for the information. Yes its a SEOS AC 808s
Its is only white text ( sub-titles) that shows up the defocus. I will leave good enough alone and go back to looking at modding the VNB.
Thanks,
Greg.

[gjaky]

A few years ago I "invented" the reddish subtitles, if you can set the color of the subtitles it is really worth it. White subtitles on screeen always decreasing the interscene contrast, by lighting up the room and by bouncing in the AC system. Using reddish-purple subtitles suffer far less from these effects. The red has very low luminence, still easy to read, just a tip.

[garyfritz]

That's a cool idea! How did you change just the subtitles?

[gjaky]

I use HTPC, with that, this is easy.