(Read the whole post before you delete it for being off-topic, mods! :))

I just scored a 1080p CRT rear projection TV on craigslist for $0. It's got a busted convergence board, etc, so I hunt down the part and have myself... well, a big but kinda lousy RPTV.

But the whole thing got me thinking - how do the specs and setup of a CRT RPTV differ from front projectors? They're still being made in fairly large quantities, and they can achieve reasonable resolutions. I'm presuming that they have to be fairly bright in 'real' terms, because I would think you lose a lot of brightness when you rear project. And I know that some Barcos (808s in particular) were packaged as RPTVs.

And I know that the Toshiba I'm dragging home this evening has user-accessible convergence, so if you rejiggered things mechanically to get it close you could probably converge it.

So, has anybody tried gutting an RPTV, putting some HD145s on it, and using it as a front projector? Presumably you'd need to feed it flipped output as it would expect a mirror and not have options to compensate, but that's not so bad (downright easy with an HTPC).

Anybody know what kind of hardware is really in these things? Or if really their funky lenticular screens that yield such horrific hotspotting and viewing angle performance mean they're actually super dim if you front project?

The icing if this was at all feasible would be that most of these already have DVI and HDCP inputs so the signal path is quite nice; digital right up to the PJ.

(Yeah, another crazy pie-in-the-sky idea. I know. But speculating on stuff like this is lots of fun for me. Please accept my apologies if it's getting old!)

They're still being made in fairly large quantities

What, CRT RP's? Where have you been finding them lately?

There have attempts to convert a Barco 808 Retro (a retro is an RPTV in the professional world) to front projection. I think someone was successful. The advantage to doing this is that the 808 Retro is LC coupled whereas no 808, other than the Cine8 Onyx and Zenith badged PRO 1200, are LC coupled. Actually, many RP's are LC coupled. One downside is that the lenses are very short throw so you'll need a set of longer throw lenses to make it work (unless you're happy with a really small screen; small, at least, from a front projection point of view). Other than the 808 Retro, I don't see any advantage to a RP-to-FP project, other than the fun of it. For all your effort, you'd be better off getting a front projector; they're really cheap now.

I'm basing my "fairly large quantities" on what I'm seeing people selling second hand, and on the fact that I seem to recall seeing them in Best Buy recently. I could be wrong about that. But either way, there are plenty of 2004-vintage RPTVs about, which is newer than FPs tend to be.

I've got a front projector (808s) I'm happy with, but having accidentally scored an RPTV it started me thinking. In particular, if the brightness is there (as far as I can tell, most RPTVs are 7" CRTs), they're relatively small packages, high resolution (at least, spec-wise) compared with all but 9" PJs, and as I mentioned, tend to take DVI/HDMI directly.

My best guess is that the limiting factor would be the optics setup; you'd have to substitute lenses and then it'd be an issue of getting them set up right to resolve a 1080p image well.

Yeah, mainly I'm thinking it would be fun to play with (I've always gotten a charge out of doing things that make people go, "You WHAT?") but if nothing else I could mod an RPTV to do a short-throw front projection display for my office... :)

I have a retroblock G808s that has HD117-24 lenses on it, is LC and was probably from a RPTV, the Barco lens calculator says that I would get a 3.5 metre wide screen with it set up for front projection where my Sony VPH1000QM is set up and that gets a 2.8 metre wide screen.

It has 8" PT18-244 tubes.

I would like to get some lenses for it that would allow a 2.8 metre wide screen instead of 3.5 metre wide.

I have what I think is a similar question. I have a RPCRTand I wonder if it's possible to apply some of the same mods done to a FP.

Generally no, it's a waste of time. RP Sets use LC tubes with short throw lenses. The rear curve of the lens isn't compatible with the HD18 FP lenses that are LC, so you;d have to do a complete LC swap of the hardware and lenses. Try to find some LC lenses, the HD 18s. NOt an easy thing to do.

In addition, the lens toe in is set for a small screen, so additional metalwork would be required.

Why is a 1080p RP set not stellar looking? If the tubes are worn, then I can see why, but an RP 1080p image should look the same as a 1080p FP image.

The only reason I got my RPTV is because the price was right - $0.00. Well, $50 once I get it running.

I generally dislike RP images; they've got a sparkly 'unreal' quality to them because you're looking at a virtual image rather than a 'real' one, either emitted or reflected. Because of the way they work, each eye sees a slightly different image, and that translates to me into a weird feeling where I'm looking *through* the screen rather than at it, and it's disconcerting to say the least.

If that wasn't enough, they usually have absolutely horrific hotspotting (the newest DLP RPTVs I've seen aren't *awful* but are still very, very bad - less than 80% uniformity as far as I can tell subjectively) and lousy black levels to boot. Honestly I'm not sure why anybody ever put up with the things they're so bad.

The only reason I'm considering using one now is because our old TV is a busted up 27" direct view which is far too small for the space and because the digital I've been using will toast up its lamp and would be useful in my office for other stuff.

But for me, RPTVs are a desperation measure in terms of quality. I can't imagine watching movies on one in a million years.

Generally no, it's a waste of time. RP Sets use LC tubes with short throw lenses. The rear curve of the lens isn't compatible with the HD18 FP lenses that are LC, so you;d have to do a complete LC swap of the hardware and lenses. Try to find some LC lenses, the HD 18s. NOt an easy thing to do.

In addition, the lens toe in is set for a small screen, so additional metalwork would be required.

Why is a 1080p RP set not stellar looking? If the tubes are worn, then I can see why, but an RP 1080p image should look the same as a 1080p FP image.

Ok, you say generally, not definitely. Are there other mods that can be done to improve performance of a RP beyond the lenses? I read a lot about mods to increase bandwith and improve the video chain, are these not applicable to a RP?

I generally dislike RP images; they've got a sparkly 'unreal' quality to them because you're looking at a virtual image rather than a 'real' one, either emitted or reflected. Because of the way they work, each eye sees a slightly different image, and that translates to me into a weird feeling where I'm looking *through* the screen rather than at it, and it's disconcerting to say the least.

Sorry, I'm having trouble understanding this...real vs. virtual image? Emitted or reflected? What exactly do you mean? It's been said in this forum that a RP screen can give you the best picture quality (starting with a good quality projector of course; we weren't talking about all-in-one RPTVs, but your comments would seem to apply to CRT projectors in RP installations as well...).

Sorry, I'm having trouble understanding this...real vs. virtual image? Emitted or reflected? What exactly do you mean? It's been said in this forum that a RP screen can give you the best picture quality (starting with a good quality projector of course; we weren't talking about all-in-one RPTVs, but your comments would seem to apply to CRT projectors in RP installations as well...).

In theory, you could build a rear projection setup that was extremely good by using a matte white screen surface which diffused light evenly. But this would require absolute light control, just like for front projection - its biggest advantage as far as I know would be in terms of the ability to keep the CRT face geometry aligned perfectly with the screen, and to maximise phosphor usage.

In the real world, RPTV designers have to design for high ambient light, which means making a screen that looks black from the outside but lights up evenly from the inside. This is not terribly easy. :) And because RPTVs are sold to the 'unwashed masses' they have to sit next to other RPTVs and plasmas, and so the main goal of the engineers has to be to make them brighter than their neighbors, which attracts people - rather like moths.

So you get hotspotting - you let more light out but sacrifice uniformity and black level, because you have to both let more light IN *and* use funky lenticular restrictors that only let you see the image from specific vantage points, in order to cut down on light getting back into the RPTV box.

As far as the oddness with the image goes think about it this way: A hotspot is essentially a way of saying that you're seeing an out-of-focus version of the CRTs straight through the screen. And since each eye sees a different version, you sense that depth and it's hard to focus on the screen surface itself.

Virtual images happen when rather than diffusing the light against a surface, the entire image is generated via a lensing system, a bit like a fresnel. The lenticular screen doesn't have an image on it so much as redirect the light toward your eyes (this is not a very good description...) so you're not seeing something that's 'really there' on the surface of the screen. Which, of course, is why it goes away if you move.

My guess is that RPTVs use a combination of those techniques, and I'm certainly not an expert, but that's my guess. Anybody who knows more and has a better explanation is welcome to smack me down. :)

...but, to keep it on topic, that's why I prefer front projection. :D

Hi guys,

We just got in brand new in the original Barco box some RetroBlock projectors. Looking at the threads we originally thought that these projectors couldn't be used in a front-projection configuration but they can! We've got one setup with a 105" widescreen picture with no problem.

In fact it appears that with the HD-117-12's on the projectors you could go out to about 110" screen and still be okay with the adjustments which falls in line with the 2.5m size stated above.

The projectors use the P16LNP07/47 series Liquid Coupled tubes and as I've stated above they are brand new in the original box with only 100 hours burn-in on them. You can see pictures at Videogon or ebay as we have them running in both places.

http://cgi.videogon.com/cgi-bin/cl.pl?projcrta&1196114872&class&3&4&

http://cgi.*********/New-Barco-Graphics-808s-RetroBlock-CRT-Projector-P16LNP_W0QQitemZ280157236890QQihZ018QQcategoryZ32862QQcmdZVi ewItem

We have seven of them left and one set of tubes from one that we parted out.