CurtPalme.com Home Theater Forum

[Melifluonze]

I could have sworn there was some thread about adding a stray light mask into the optical path of an 8500, like a black disk with a hole in the center. Just like the iris of a camera, when stopped down, gives you better (sharper, more contrasty?) pictures.

Can't one add a disk like this to the lens system? Or is the halo effect created right in the glass of the front of the tube?

I bet there's some kind of a little trick...

And, suppose you stack four 8500 Ultras... does stacking them reduce the halo, or is it just additive and it shows up anyways?

- Melifluonze

[Curt Palme]

Yep, I've had a few sets in where black matte paper blocks all of the tube face but the used area of the raster. It will block some of the halos, but not all.






You're just going to outdo my stack, aren'tcha?

[Curt Palme]

Yep, I've had a few sets in where black matte paper blocks all of the tube face but the used area of the raster. It will block some of the halos, but not all.






You're just going to outdo my stack, aren'tcha?

[Melifluonze]

Err... If I never, ever post about it... then it doesn't really exist, does it? Oh wait... I just posted...

It'll take me forever to do anything (if you haven't noticed), but the HT hobby is swinging back into place now that winter is coming.

What about glycol in the 8" tubes... can you replace the glycol in the front of the 8" AC tubes with the tinted stuff and improve color?

*goes off to search threads...

[ecrabb]

The halos are caused by light reflecting back off the rear lens element on the lens, back onto the tube face and lighting up the phosphor. It's also a cumulative effect, meaning there isn't just one bounce; that bounce happens several time until it fades out. An LC setup avoids the most glaringly (excuse the pun) visible part of the problem by using a convex lens, so any light that does reflect back toward the tube face is spread out over a much larger area. So, instead of an obvious halo, it just has the effect of reducing ANSI contrast with a mostly invisible visible "halo" larger than the screen.

There's no way you could use any kind of disc as an aperture because you'd have to do it inside the lens. If you could disassemble the lens and insert an aperture, the net effect would darkening the halos, but also reducing the overall light reaching the screen, and CRT ain't so hot in that area to begin with.

NEC XG LC projectors had some small strips of tape added at the top and bottom of the C-element. I assume the engineers tested and found some improvement (I'd guess a small overall increase in ANSI contrast), or they wouldn't have bothered with the modification in the first place. I was always going to do the mod on my G70 to see if I could see or measure any difference in ANSI, but never got around to it.



It would be very easy with an AC projector to cut some nice black PVC (or PVC with black Fidelio velvet laminated on) to fit between the tube face and rear lens element. It would definitely be worth trying, and I'd definitely do it if I still had an AC projector. I'm not sure how much it will reduce halos - probably just a little at the top and bottom of the screen - but it would be worth trying.

Wait. Hold on… Not to be cruel, but if I had an AC projector, I'd be looking for an LC projector. Seriously. Biggest upgrade you could possible make. 8-inch LC machines are damn near free these days, and would be a huge step up in image quality over an AC machine. The halos alone are with the trouble of upgrading. That's my two cents, anyway.

Cheers,
SC

[Melifluonze]

I agree with everything you said... And I'm running LC as my primary projector (9500LC Ultra), but...

I'm a hardware junkie and Nash got me all worked up on the blending thing with his threads, so I went off and bought a bunch of 8510's (like Curts) and some TVOne video scalers.

I'm going to fix up the 8510's a bit (bad tubes in ALL of them... ) and try some scenarios just to see where things go.

It's really cool that this stuff has finally come down in price enough to experiment! It's a dream come true!!!

- M

[Melifluonze]

AND... Curt... I see your thread! You're stacking freakin' Barco 909's... I'm just stacking little 8" Electrohome toys...

[Nashou66]

I have tubes for those 8500's. From my 8500's but they are AC tubes and i think yours have P16's. Is that what the 8510's have? I thought curts were 8 inch LC tubes? If they are P15's we might have to look at the VNB's and move the jumpers for the 180DMB's of the Marquee's I have.

When can you come down to see the blend? its only an hour away !!! drive down one day we can watch a flick then you can be home by midnight.

LOL
'

Nashou

[CasetheCorvetteman]

Stridsvognen did this a while ago, spent a fair bit of time on it, made some claims, had a debate, then went back to LC.

[Melifluonze]

Pretty sure they're AC. They're the 8510 Ultras.

[stridsvognen]

[CasetheCorvetteman]

If youre projection on a white wall with no dark boarder and all other walls/ceiling are light colours, it wont be worth the effort either way, better off spending far less effort painting some darker colours to reduce reflections of light off room surfaces.

[redfox001]

I have LC lenses and when there is a black background with white letters to the side the letters mirror readable to the other side of the screen. Very clearly visible. Is this normal? Is asked before but noone reacted so I think noone knows what I am talking about? It is disturbing

[CasetheCorvetteman]

No, its not normal at all. Ive not seen it myself, better look to see you have glycol in there!!

[redfox001]

[CasetheCorvetteman]

It could be empty!

[Nashou66]

Sounds like Streaking. Older Marquee VNB's did that if the main input caps were going bad.

Nashou

[CasetheCorvetteman]

Get the ESR meter out and have a gander...

[draganm]

[barco_75]

Stridsvognen can you post the link of the debate? I'm curious what the properties of the material you used and the technique followed. I'm pulling my tubes now, so maybe I can try it.

[stridsvognen]