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Post by gjaky on Oct 28, 2018 16:42:09 GMT -5
In our new house I'll be "allowed" to occupy the biggest room in the basement, that is roughly 7.5m x 4.25m. This would be far too big for theatre use only -at least for our needs, so I would move my electronics lab there as well.
As for the theatre the main problem is that the height of the room is only 210cm, so hanging down the projector from the ceiling is not very good idea. Putting on the ground would take the best seat out of the cinema wich is unfavourable as well.
So I am flirting with the idea to do a rear projection setup in that room, It would be relatively easy to put up some drywall to cut the room in two, so the projector could reside in one side of the room, which would be -by coincidence- my electronics lab as well, while the cinema could be virtually silent of fan noise on the other part of the original room. Awesome, right?
But I am unfamiliar with rear projection screens, I guess they are somewhat special breed, and hard to find, thus very expensive. I am thinking about a ~2m wide screen (16:9), as I'd have to leave space for a door on that wall obviously. I also have a preconception that the light loss of the rear projection screen is considerable, is this right?
I am curious what are thinking about this?
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Post by Admin on Oct 28, 2018 16:50:52 GMT -5
To bad you are so far away. I have a rear projection mirror system (commercial) that I have been thinking about throwing out. As to your question, my research of RP flexible screen material (years ago already) are quite advanced and work very well from what I remember. Price was not bad also. I just never fully decided to go with it.
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Post by Casethecorvetteman on Nov 1, 2018 10:07:23 GMT -5
Gabór, i have only ever done one rear projection setup and that was many years ago, and using a 1280x800p high end ( at that time ) commercial DLP.
The projector i set up was around $28,000 AUD and almost as large as a smaller Sony CRT, such as a 1000 series. From memory it had 2 bulbs.
It was bullshit bright, and actually had a reasonable contrast ratio too.
Its hard for me to gauge how good it all was as i had no experience with that machine on a front screen, and there was no way any 1 CRT wouldve lit up this screen well enough to be usable as it was around 6.5 meters wide and 16:10 format, so it was effing huge. A Reality 912 may have been a chance, but ive never seen one, and i doubt they'd be that bright.
The image quality was quite good from a distance, but had a slightly blured appearance up close, somwhat simular to older rear projection TVs when you look real close.
Im not sure is all rear projection screens are like this, from 10 meters back it looked good, but at 3-4 meters it wasnt as razor sharp as id expect from a front projection setup.
This screen gave reasonably good blacks even with the lights on, due to the fact that with the projector off the screen was a dark grey colour.
My Cine 9 is only 1850mm from the floor, which gives me a good 100-125mm clearance to walk under, so no dramas at all. Im not sure what CRT youre using these days, but that would give you around 250mm to play with, and if you could get the projector partly into the ceiling space above you, that gives you even more.
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Post by gjaky on Nov 1, 2018 14:19:44 GMT -5
I have a Marquee 9500 and with my DIY ceiling mount the lowest point is 50cm below ceiling, with the given 210cm height the clearance would be 160cm, and I am 196cm tall by the way, so ceiling mount is clearly out of question...
As for rear projection, RPTVs all had Fresnel lenses behind the screen, to my understanding this help with light uniformity. But clearly not every RP application have them, so what's the deal then?
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Post by barclay66 on Nov 2, 2018 5:16:53 GMT -5
Hi, To my knowledge, Fresnel lenses have no practical use in conjunction with CRT projectors. They are mostly used for LCD projedtion instead of a much larger lens type ( Fresnel -> Section Projection). Almost all of the rear projection setups I have seen, suffered from a very prominent hot spot and allowed only vor very small viewing angles. Instead, I would suggest mounting the projector vertically to the wall (Lenses upward) and using a 45 degree surface mirror... Kind Regards, barclay66 |
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Post by Casethecorvetteman on Nov 2, 2018 18:18:08 GMT -5
Hi, To my knowledge, Fresnel lenses have no practical use in conjunction with CRT projectors. They are mostly used for LCD projedtion instead of a much larger lens type ( Fresnel -> Section Projection). Almost all of the rear projection setups I have seen, suffered from a very prominent hot spot and allowed only vor very small viewing angles. Instead, I would suggest mounting the projector vertically to the wall (Lenses upward) and using a 45 degree surface mirror... Kind Regards, barclay66 Yes, the one i set up had very bad hot spotting if you were not on the angle it was set up to be viewed at, and brightness uniformity was pretty ordinary especially near the corners |
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Post by gjaky on Nov 3, 2018 17:02:51 GMT -5
I've not seen an RPTV without a Fresnel lens. As is the light coming out of the "light engine" (let it be anything) the light out of the lenses) have a cone angle, but unlike the front projection this light is not scattered fully on the screen, therefore it is desirable that the light beams passing a rear projection screen are as parallel as possible. I think the lack of Fresnel lens contributed greatly of the hotspotting of the setups you mentioned. This also means I'll be in trouble to getting a 2m wide (custom) Fresnel lens... 
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