JBaymore wrote on May 18th, 2007 at 10:20am:| Sounds like you favor lcd in this application. Yes? More on why? At this point I am planning on XVGA......... 1024 x 768. MIGHT go one up from there.... but unlikely due to still high price. |
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DLP is fantastic stuff... really shines when watching movies. But I personally feel it doesn't offer much improvement for VGA sources. However, I tend to forget, since I install these things but don't sell them, that DLP is not a very pricey option anymore... it's really not an issue, even in the under-$1500 range of portables. Also, the "native" res. of most of these types is 1024x768, but most will go higher.
Quote:| I don't know HOW keystoning works... just that it does. 8-) Removing visual data DOES sound like a bad idea.... so what is the alternative? And what do you mean by "de-keystone"? |
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By "de-keystoning" i mean negating the optical keystoning effect digitally. The way the unit does this is by dropping pixels and/or adding edge pixels... seeing as how it can't alter the size or shape of each pixel, it's the only way.
Generally, for non-VGA sources, it looks OK even when you've maxed-out the keystoning ability of the projector, but images coming from a PC can show nasty phasing effects if a lot of digital keystoning is used. This is generally more of a problem with text and static graphics, but I prefer to avoid it as much as possible whenever I have the option of an optical solution.
Quote:| So if using keystoning is not good ...... and the projector HAS to be mounted at an angle to the surface that it projects upon, HOW do you do that and get a "normal" image. I can't see how mirrors would actually help in that regard. |
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Logical assumption... but let's say your projector is set at a 45-degree angle from the centerline of the screen. If your mirror is at a 45, the image will hit the screen "square". Making this happen can be a major PITA, but it's worth it. Needless to say, with mirrors you can get into more of a keystoning mess than you started out with, but it can be done. Typical rear projection setup I deal with is a large "window", actually a translucent RP screen... behind it is a little room with a frame made specifically for the projector in question. Said projector faces away from the screen, tilted up slightly. It throws the light at a mirror, set up at a reciprocal angle so that the image hits the screen at a right angle. The mirror is primarily to increase throw distance without taking up a lot of room, but since the light has to make a "180" in such a setup, obviously the matching angles will eliminate keystoning (ideally).
Quote:| I was likely planning on a "one bounce" mirror situation anyway in order to double the throw distance I have, and use the rear projection" approach to correcting the reflected reversed image. One thing I need to research is geting a really GOOD mirror. |
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You don't have to go crazy with the mirrors... believe it or not, many pro installs involve a mirror that is simply mirrored mylar sheet stretched on a frame. Looks great. I bet with a little care and the right mylar, you could make one yourself. They're super-lightweight, but of course rather fragile. the most important thing I've found is that whatever the mirror, it should be clean and flat. REALLY flat. Even expensive glass mirrors can get mounted so that they are twisted... very bad.
Quote:| For ventilation I was planning on adding some active fans in the projector mounting area anyway to improve air circulation. I know that won't take care of INSIDE the unit... but it'll improve the general environment around the unit. |
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Other than experimentation, if the recommended mounting angle isn't published there's not much you can do. But I will say that those units (all the lower-priced Sanyos spring to mind) that have limits usually do not like to be mounted at more than a 15-degree angle. The problem with such projectors (which are made to hang from the ceiling or sit on a table) is that the case cannot vent properly at more than a certain angle.
Best advice i can give is to not buy anything unless you can download a manual or ask someone on the phone.
Quote:| I assumed that I need a short throw lens of some sort. Any suggestions on that? In fact what is the best short throw "stock" projector that you know of? |
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I don't think there is a unit that comes "stock" with a short-throw lens... but before contemplating this, determine what your throw might be, and simply pick a unit with a stock lens that will accommodate. I HIGHLY recommend any projector with a ZOOM lens, and lens shift capability (allows you to shift the image without tilting). Lens shift is often motorized, and often limited to one direction... best type has manual horizontal and vertical lens shift... an installer's wet dream.
Like I said, I don't sell or shop for projectors, I just make do with what they give me. But I like:
NEC (great price range; low-impact keystoning; good zoom lenses- but not all have lens shift)
Panasonic (just really good quality; only have experience with the pricey ones, but they also have quite a few models)
The Epson PowerLites look pretty good, too... manual H/V lens shift and 720x1280 native res., and low price.
Recently installed a projector with similar features, and I thought it was superb... think it was an Epson, but have to check on that. :-[
