# Rear projection system



## renegadeblack (Jan 5, 2009)

I was thinking about a possible rear projection system for in our auditorium. I've already been told that we're going to be getting a permanent projector put into place and they're asking the crew for suggestions.

I was thinking about a rear projection sort of thing. Although we don't have a projector now, we do have a screen that comes down right in front of the main curtain. I was thinking about some sort of rear projection screen to go right there and then maybe if the projector could be on some sort of motor that would lower it down to the necessary level so that when it's not in use, its way up in the ceiling (we don't have a fly system, though it is a pretty high roof). Anyone know of the viability of such a system?

I've been told that they want to get an HD projector, full HD. I'm wondering what we could get for less than $10K. Probably about a 100 in image fairly bright, I'd like to hope I could maybe even have the stage lights on when we're using the projector, but maybe not.


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## photoatdv (Jan 5, 2009)

I don't know about the motorized projector, though I know its possible. The rear projection setup in terms of the projector is generally easy. Most decent projectors have the option in the setup menu for front ceiling, front floor, rear ceiling, and rear floor. For that setup it would be rear ceiling.


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## waynehoskins (Jan 5, 2009)

Just note that if you're talking about real HD, you're talking about a high-end real projector. Pricey, but probably plenty bright ('cause you'd be talking about a 5K or a 10K there).


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## mixmaster (Jan 5, 2009)

You're definitely going to want a high lumen projector. I know when we do graduation in the Fieldhouse, we have to superimpose 2 3000 lumen projectors to get an image bright enough to be seen with the lights on. And it's still not any too bright. We get by with a 2000 lumen in our performance spaces for lectures as long as we don't have stage lights washing the screen, but chapel service uses the 2000 lumen with stage lights and we have to make some creative shuttercuts to light the whole stage but not throw light on the screen. We've been talking about getting a bigger one and I think we decided that we won't even consider a projector with less than a 7-8000 lumen rating. 
When we rear-project, we either hang the projector from a batten, or set it on top of a ladder, depending on the venue and the needs. Neither is a permanent mount. We want it flexible so we can use it as a front projector for small venues with a portable screen, hung for rear projection onto a screen, or turned around and shot to the Cyc for a huge back drop image. I think our next one is going to have the ability to change lenses too, to accommodate different uses. That would be something else to think about.
Matt


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## renegadeblack (Jan 5, 2009)

mixmaster said:


> You're definitely going to want a high lumen projector. I know when we do graduation in the Fieldhouse, we have to superimpose 2 3000 lumen projectors to get an image bright enough to be seen with the lights on.



That is an absolutely brilliant idea. I had never thought of something like that, I know about stitching projector images together to make a wider screen or eliminate shadows, but for brightness is a real good idea.

Mainly what I was looking for though was verification on whether or not a motorized projector would work. If anyone thought it would be a bad idea.


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## icewolf08 (Jan 5, 2009)

renegadeblack said:


> Mainly what I was looking for though was verification on whether or not a motorized projector would work. If anyone thought it would be a bad idea.



Not only would it work, it is a pretty standard thing. I would imagine you can find many manufacturers of projector "lifts." It is very common for people to install projectors on a lift such that they can tuck out of the way when not in use.


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## museav (Jan 6, 2009)

Here are a couple of long drop projector lift manufacturers, Display Devices - Products - Projector Lifts and SVS PROJECTOR LIFTS. Be aware that the lifts I have typically seen installed in Auditoriums would require a good part of your $10k budget, probably 50% or more for an installed lift and you also have to get power to it.

Stacking projectors can be a way to get more brightness but the two projectors have to be carefully converged and will often require tweaking to keep that convergence, especially if on a motorized mount. And the higher the projector resolution, the more critical and difficult the convergence.

Which segues to the comment about "full HD". 720p (1280x720) and 1080i/p (1920x1080) are both "full HD" and many current projectors are not a 16:9 HD format native resolution but rather a computer graphics resolution with a 15:9 or 16:10 native format. Do you actually mean that you want a 1920x1080 resolution projector?

You also mentioned a 100" image, but is that the height, width or diagonal? A 100" diagonal HD image is 49" high, so just over a 4' high image. That would be a bit small for most auditoriums, with about a 24.5' to 32.67' recommended viewing distance and maybe a 41' recommended maximum viewing distance.

It is not always practical but what I have done in several new facilities is to build a projection recess or port into the upstage wall so they can incorporate rear screen projection with the projector actually recessed and outside the stage proper but accessible from the ceiling of a corridor or other space behind the upstage wall.


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## mixmaster (Jan 6, 2009)

renegadeblack said:


> That is an absolutely brilliant idea. I had never thought of something like that, I know about stitching projector images together to make a wider screen or eliminate shadows, but for brightness is a real good idea.



In all honesty, the schools has been doing it since before I came on board,so I can't claim it as my idea. It requires two identical projectors. Most projectors have a focusing pattern in a set-up menu. It's simply a matter of projecting the pattern from both projectors on the screen and lining them up. It's not technically very difficult but trying to get things lined up can be exasperating and frustrating. On the scale we use, if it's off by a single pixel in any direction then things look out of focus. Took me an hour and a half last year. Unfortunately, the powers-that-be say they can't justify the cost of a new projector for a once a year event.  Never mind the fact we do it once a year, EVERY YEAR! Arrg.


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## museav (Jan 6, 2009)

mixmaster said:


> It's simply a matter of projecting the pattern from both projectors on the screen and lining them up. It's not technically very difficult but trying to get things lined up can be exasperating and frustrating.


It can be much more complex than that, to get an accurate image color, brightness, contrast, gamma, etc. should also be matched, not just pixel overlay. If the projectors have any significant physical separation it can be even more difficult to get them aligned, the physically closer they are to each other and to the ideal location relative to the screen, the better.

You also want to be sure to do any alignment after the projectors have reached a steady state temperature, the lenses will expand from the heat until they have a chance to stabilize and the expansion can be slightly different so projectors aligned cold may no longer be aligned after running for some time.


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## mixmaster (Jan 6, 2009)

museav said:


> It can be much more complex than that, to get an accurate image color, brightness, contrast, gamma, etc. should also be matched, not just pixel overlay. If the projectors have any significant physical separation it can be even more difficult to get them aligned, the physically closer they are to each other and to the ideal location relative to the screen, the better.
> 
> 
> You also want to be sure to do any alignment after the projectors have reached a steady state temperature, the lenses will expand from the heat until they have a chance to stabilize and the expansion can be slightly different so projectors aligned cold may no longer be aligned after running for some time.



Yep. And don't forget having to match the zoom, focus and any necessary keystone. That's why it takes me an hour and a half. We have a custom cabinet that was built specifically for the projectors with cooling fans and video distribution and AC outlets. After we mount up the projectors and restore factory defaults, I go through each menu item to make sure that everything is returned to default and then we can start the alignment process. It would be a heck of a lot simpler to just get one big projector, but,hey what do I know? The powers the be just tell me We've always done it this way and it always works. (have you heard that one before?)
I hadn't thought about the lenses expanding. I wonder if the expansion would necessarily be the same from show to show. I'm guessing not, which would account for things being slightly off from one day's rehearsal to the next.


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## renegadeblack (Jan 6, 2009)

museav said:


> Here are a couple of long drop projector lift manufacturers, Display Devices - Products - Projector Lifts and SVS PROJECTOR LIFTS. Be aware that the lifts I have typically seen installed in Auditoriums would require a good part of your $10k budget, probably 50% or more for an installed lift and you also have to get power to it.
> 
> Stacking projectors can be a way to get more brightness but the two projectors have to be carefully converged and will often require tweaking to keep that convergence, especially if on a motorized mount. And the higher the projector resolution, the more critical and difficult the convergence.
> 
> ...



Actually, I guess that is a very small image. I don't know the dimension of my proscenium, but what I would sort of like to do is have a CYC that is in the same place as where the curtain normally goes and project onto that and maybe even fill the entire thing, or atleast close to it. Also, being as a lift would be so expensive, what about having the projector all the way back in the booth? That's probably about 100 feet, maybe 150 away. Will that be something possible? Also, all that they said was that they wanted a full HD projector.


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## porkchop (Jan 7, 2009)

museav said:


> Here are a couple of long drop projector lift manufacturers, Display Devices - Products - Projector Lifts and SVS PROJECTOR LIFTS. Be aware that the lifts I have typically seen installed in Auditoriums would require a good part of your $10k budget, probably 50% or more for an installed lift and you also have to get power to it.



I don't see any need to spend that much on a lift. On our show we have two Barco projectors mounted with the standard clamps went with them and a daisy chain to a 10' stick of truss held up by two CM Loadstar 1/2 ton motors and it works great. The OP said there's no fly system so you don't have to worry about snagging battens. I don't know what 2 chain motors cost but two of them, a stick of truss, and the necessary rigging materials must be significantly cheaper than $5k. 

Also if you can go the route of multiple projectors I can't recommend enough that you overlap the picture over stitching the pictures together. If you have any kind of problems with one of the projectors, that part of the image will be noticeably dimmer. If you overlap though all you have is a reduction in intensity. We completely changed the rig of our projectors for this exact purpose. Also you don't need any kind of multimedia server to split the image so your saving money on equipment if you overlap.

The bottom line is going to be the more money you can spend the brighter and more defined a picture you'll be able to make. but there are lots of solutions that can make you happy with your $10k budget.

AFTER THOUGHT: I'm a bit spoiled with my projectors so my situation might be different, but you should also keep power in mind when you figure out your projectors. My power run is 2 x 50A 120V (one for each projector) and 2 x 50A 120V 3 phase (one for each motor). I wouldn't imagine most theatre spaces have that kind of power service kicking around. You probably won't end up needing anywhere near that much but just a thing to keep in mind.


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## museav (Jan 7, 2009)

porkchop said:


> I don't see any need to spend that much on a lift. On our show we have two Barco projectors mounted with the standard clamps went with them and a daisy chain to a 10' stick of truss held up by two CM Loadstar 1/2 ton motors and it works great. The OP said there's no fly system so you don't have to worry about snagging battens. I don't know what 2 chain motors cost but two of them, a stick of truss, and the necessary rigging materials must be significantly cheaper than $5k.


Based on the quotes I recently received for flying a couple of speaker arrays on chain hoists and on some online pricing for the 1/2 ton CM Lodestar hoists, by the time everything was accounted for, I doubt that it would save that much.


porkchop said:


> Also if you can go the route of multiple projectors I can't recommend enough that you overlap the picture over stitching the pictures together. If you have any kind of problems with one of the projectors, that part of the image will be noticeably dimmer. If you overlap though all you have is a reduction in intensity. We completely changed the rig of our projectors for this exact purpose. Also you don't need any kind of multimedia server to split the image so your saving money on equipment if you overlap.


By "stitching together" do you mean edge blending?


porkchop said:


> The bottom line is going to be the more money you can spend the brighter and more defined a picture you'll be able to make. but there are lots of solutions that can make you happy with your $10k budget.


I have to disagree. If it was $10k for just a projector, then maybe, but if the $10k also has to cover all mounting, installation, cabling, power and so on as well as a projector for an auditorium, and especially a projector being shown on a cyc rather rather than a real screen, then that is a very tight budget.

In fact, other than maybe the Mitsubishi FL6900U at 4,000 lumens or the Optoma HD81-LV at 2,500 lumens, a $10,000 budget for a 1920x1080 native projector puts you in the under 2,000 lumen category, probably less output than you would need. But make it a 1280x768 or similar native resolution that would support 720p HD and you can easily get 4,000 to 5,000 lumens well within your budget with a number of projector options available.

Having the projector at the back of the auditorium and using front projection is an option, but it would typically require a projector that had a long throw lens option and the lenses tend to be expensive.


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## MikeyHP (Jun 12, 2009)

We JUST put a rear projection system in our PAC. We hung a 16x24 cyc and used a 3000 lumen projector... Works well except that we are going to need to buy a 5000 lumen projector (oh darn) the cyc was from Norcostco for around $950.. the new projecter will be an inFocus and will cost around $5000. ( the projector is 1080P with HDMI and tons of other inputs.


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## museav (Jun 12, 2009)

MikeyHP said:


> We JUST put a rear projection system in our PAC. We hung a 16x24 cyc and used a 3000 lumen projector... Works well except that we are going to need to buy a 5000 lumen projector (oh darn) the cyc was from Norcostco for around $950.. the new projecter will be an inFocus and will cost around $5000. ( the projector is 1080P with HDMI and tons of other inputs.


A 24' wide 1080p image would be 13.5' high, 24'x16' is a 1.5:1 or 35mm slide format. And assuming a gain of 1, which might be very generous depending on the cyc material, 5,000 lumens over a 24'x13.5' image area would be 15.4 ftL, below the SMPTE recommendations for a cinema with very controlled lighting and that's would be with the standard lens and a new lamp. It may work great for you but the numbers don't really seem to match up.

I did not realize that InFocus made anything like that, when I last looked their 1080p native projectors were all home theater oriented and under 2,000 lumens while their only 5,000 lumen projector was 1024x768 native resolution. Have they introduced a new 5,000 lumen, 1920x1080 native projector with that low a price? I'll have to check at InfoComm next week.


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