CurtPalme.com Home Theater Forum

km987654 · Posted: Tue Feb 26, 2013 8:49 pm Post subject: How out of focus should blue be??

Just taking a closer look at my setup and I was wondering how out of focus blue should be. I can not make it sharp no matter what I do and it seems really out of focus. The picture looks good but it could be better.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

It should be pretty fuzzy, unless you have a video processor that lets you tweak the blue response curve. (And you don't mind toasting your blue tube.)

In normal video you'll never notice it unless you really look for it. Might see a blue fringe around white text on black background.

km987654 · Posted: Tue Feb 26, 2013 11:08 pm Post subject:

Thanks.

You cannot see any blue halo and picture looks good so all is well it would seem. Its just when looking at an only blue pattern you go cross eyed trying to focus your eyes on the pattern.

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

That's not just your projector. Your eyes don't SEE blue very well. Try looking at blue and red Christmas tree lights (or similar) in the dark. The red looks sharp, but the blue is a fuzzy blur. Apparently your eye's lenses are "tuned" to the red end of the spectrum, and there is some chromatic aberration at the blue end.

Zolzar · Joined: 26 Jun 2009 Posts: 252

I know with my NEC that when I turn on the defocus switch it is enough to give the cross batch pattern a slightly blue "glow" or halo. Only slightly though.

**kal** · Posted: Wed Feb 27, 2013 2:23 pm Post subject:

On my Zenith 1200 I would get optical focus as good as possible and then purposely defocussed blue electronically (at 0 on a range of 0-100) to boost light output for a better greyscale.

Blue was a horrible fuzzy mess but you don't see it on content.

Kal

km987654 · Posted: Wed Feb 27, 2013 8:12 pm Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

You can focus it electrically pretty easily. Sweep through the focus range, and when it dims, it's in focus. The brightness drops significantly when you're perfectly focused. That's WHY you defocus the blue, to get more light output.

Then you can work on focusing the optics. (Or just display a blue area and use the "focus on the phosphor grain" method, but I'm not sure how well that works on blue.) Once the blue lens is set, you can defocus electrically to get the brightness back and flatten out your grayscale.

ElTopo · Joined: 07 Nov 2006 Posts: 1640

Defocus is good but not that much. Gives you more light output tough Thumbs Up

km987654 · Posted: Thu Feb 28, 2013 8:08 pm Post subject:

kabuby77 · Joined: 28 Mar 2011 Posts: 147 Location: Italy

What's about the wear of the tube if you defocus eletrically?

barclay66 · Posted: Fri Mar 01, 2013 12:01 pm Post subject:

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

If you defocus electrically, the same electrons hit a larger area. If you were displaying dots, that would result in spreading the electrons into areas that would have been dark otherwise, and would wear your blue less than a sharp dot.

But for video content with fairly evenly-distributed blue, it shouldn't make any difference.

barclay's right -- if you tried to focus sharply, you would need to greatly increase the contrast (selectively across the IRE range, using a VP) and that would wear your blue faster.