# Rear projector help



## Pontiousw (May 8, 2010)

We are in the process of designing a show that will use rear projection. The projector we have now, Eiki LC X50M, will not work for this do to a custom lense in it.

What are the general recommendations for a rear lcd or dlp projector for a cost minded organization? It will be used in conjuction with standard stage lighting. We have 15 to 20 feet behind the screen free.

Anyone have experience with an NEC GT5000? We can get one of these for very little money.

Thanks.

Don
Resident Designer
Renaissance Theatre


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## museav (May 9, 2010)

There is additional information needed. For example, you noted that the existing projector will not work due to the lens, so what is needed in order to work? What specs are you looking for from the projector (brightness, format, resolution, contrast, lens shift, etc.)? If you don't know what specifications you need, can you provide more information on the image size, screen and so on? Do you have a budget? What do you mean by "standard stage lighting" and how does that relate to the projected image? For example, are you thinking of projecting right down to the floor where parts of the projected image could be directly washed or would the projection area not be affected by any direct light?


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## WooferHound (May 10, 2010)

I think the most important bit of missing information is the Screen Size ?


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## Pontiousw (May 10, 2010)

The screen size is 9 X 16. It will be approx 8 feet off of the floor. It is for a show with high ambient light, but non directly on the screen. We have 15 to 20 feet behind the screen. We would like a good contrast ratio and brightness. I was hoping to be at least 6000 lumens or better. Contrast would be nice at around 1000:1. Lens shift is not that important to us. Format can be any at this point.

Our FOH projector has a specialty lens in it. We have to return it to the factory to have it replaced or exchanged. This was not my doing, just what I was handed. They had to remove the standard zoom and focus motors to get this lens in. It is a rather boggerd up mess.

Thanks


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## DanAyers (May 10, 2010)

Sounds like the projector isn't the issue as much as the processor is. Take a look at Extron and see if any of the Switcher/Scaler/matrix's work for you.

Folsom (now Barco) may be another good choice. Take a look at their dealers and see what htey have in rental stock.


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## museav (May 11, 2010)

DanAyers said:


> Sounds like the projector isn't the issue as much as the processor is. Take a look at Extron and see if any of the Switcher/Scaler/matrix's work for you.
> 
> Folsom (now Barco) may be another good choice. Take a look at their dealers and see what htey have in rental stock.


Can you clarify the relevance of a processor to the issue? It sounds like the problem is the throw distance the projector optics can support and getting a large image with a relatively short throw distance. I don't see how a switcher/scaler is going to alter that.

Don, 15' to 20' of distance for the projector and throw to get a 16' wide image is going to force you into a short throw lens. You also have to consider the image format, you are looking at a 16:9 screen but both projectors noted are 4:3 format (native 1024x768 resolution) so they would actually be creating a 16'x12' image to fill the screen width.

I personally generally like NEC projectors and you mentioned it, so let's use the GT5000 as an example. It is a 1024x768 native projector, so to fill the 16' screen width it would have to display a 12'x16' or 20' diagonal image. The projector itself is roughly 22" deep, so let's say that you need 2' for the projector, leaving 13'-18' of throw available. The GT5000 uses various lenses and I don't know what lens the projector available to you has but the shortest zoom lens available for the GT5000, the GT122ZLB, would require a minimum 19' throw distance (almost 21' overall) to support the desired screen size. Even the GT10RLB fixed short throw lens would require 15'-11" of throw, which along with requiring that the projector be on the vertical and horizontal centerline of the image may or may not be feasible. So the space available may not be sufficient for the screen size desired.

In addition, because of the native 1024x768 resolution and the resulting 16'x12' image the projector would create, the image brightness of the projector would be based on that area and not just the 16'x9' screen area. Thus for the 16'x9' image you actually have only 4,500 lumens of the total 6,000 lumens of the projector. Add to that potential losses in output due to the short throw lens, lamp age, etc. and the actual image brightness might be much less than expected.

Thus the GT5000 could work for the 16'x9' image size provided that the projector comes with the fixed, short throw GT10RLB lens, that you actually have the approximately 17'-9" distance required behind the screen with that lens, that the projector can be located on the horizontal and vertical centerline of the image and that the resulting image brightness is acceptable. Chances are that the projector available to you has a different lens, so that would probably be the first thing to verify.


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