# Projector lightpower, special application



## SRHate (Jun 21, 2011)

Hi All,

I´m new here, this topic has propaply been discussed many many times before but I couldn´t find an answer that fits my scenario. 

I need to project the Aurora Borealis on a circular ceiling hung (white) surface about 15 meters of diameter. The environment is very dimly lit. In normal presentation situation I would be specifying maybe one or two 20kAlm projectors but luckily that is not the case. 

The actual purpose is just to create a atmospheric effect you don´t really LOOK at. 

Could I get away even with a 10kAlm projector?


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## metti (Jun 21, 2011)

First of all, is kAlm an abbreviation for 1000 lumens? I tried googling it and got nothing but I am going to assume it is for the purpose of this post.

Anyway, for a roughly 45' diameter circle is a pretty large screen. With low ambient light, I would expect that a 10k would have sufficient intensity but it will depend a little bit on just how saturated you need the projection to be. Since you don't want people to really look at it, the image probably doesn't need to pop quite as much and a 10k should be fine. My larger concern would be projector placement. With a screen of that size, you are going to need either a really wide angle lens or a really long throw. The fact that the screen is horizontal will mean that it either has to be really far from the ceiling for rear projection or far from the floor with a projector in the middle of the audience seating (not necessarily a problem). The alternative is getting a wide angle lens which may or may not be difficult depending on what is available locally from rental houses. The issue of coverage may end up necessitating multiple edge blended projectors even if they aren't strictly necessary to get sufficient intensity.


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## ruinexplorer (Jun 21, 2011)

Yes, kAlm is 1000 ANSI lumens. Even though other areas of the world don't necessarily abide by the American National Standards Institute, since many of the projectors are measured by this standard, it will be notated in the product literature that way.

SRHate, first off, welcome to the forum. A question about your content; do you plan on having a realistic Aurora or a stylized version (usually time-lapse)? Also, do you need to project something over the entire surface or will the image only cover a portion of the ceiling?


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## museav (Jun 21, 2011)

ruinexplorer said:


> Yes, kAlm is 1000 ANSI lumens.


FWIW, the ANSI Standard for projector lumen output measurements was withdrawn some time ago, however you still see it referenced.


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## SRHate (Jun 22, 2011)

Thanks for all the answers. The Projection surface is hung at 12 meters from the floor, so front projection it is. The plan is to use Coolux Pandora´s Box as the source, and use the warping and masking features in it. I´m afraid I will have to take the projector quite a bit off-axis though =(

Sorry about my messed up terms ;-) 10kAlm to me is 10000 ANSI Lumens. 

The content will be a composition of timelapse and still images.

If this works out, it will look SO nice up there


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## metti (Jun 22, 2011)

If it is only 40ish feet away and far off axis, you are going to need a pretty wide angle lens so check with your local rental houses to see what your options are.


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## metti (Jun 22, 2011)

Also, a Pandora's Box would definitely do what you need but it is definitely overkill for simple playback/warping and will probably cost more than you need to spend for the playback end of things. Watchout would probably be a good choice since you only have one output making it pretty cost effective. Even something like Quartz Composer/MadMapper would work and that is really cheap to rent (or even buy).


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## ruinexplorer (Jun 22, 2011)

Just to be clear, the ceiling is flat (not concave), just circular, am I correct? Since the image is "organic", being off axis will be forgiving, but it may impact the aparent brightness depending on where it is being viewed in the room. How much off axis are you talking about. This may greatly affect your ability to have a decent focus (again, maybe not too much of a problem because of the content) and could have an effect on even brightness across the image.


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## SRHate (Jun 22, 2011)

The ceiling is flat, I´m afraid that the projector will have to situated outside the circle =(

I´ll be using a Pandora´s Box PLAYER, not a server 

I think I´ll got with a Christie LX1500 and a 1.2:1 lens, the distance to the surface will be at the minimum 10, maximum 20 meters, so I´ll be projecting from a 45 degree angle :shock:


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## metti (Jun 22, 2011)

45° isn't great but for relatively organic and abstract content it is probably completely workable.


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## ruinexplorer (Jun 22, 2011)

The only issue with that angle is that the projector can only handle 10 degrees on its own, then you will need to use a top surface mirror to finish the adjustment. Here's a link to that manual. Page 7 has the details of projector mounting.


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## metti (Jun 22, 2011)

ruinexplorer said:


> The only issue with that angle is that the projector can only handle 10 degrees on its own, then you will need to use a top surface mirror to finish the adjustment. Here's a link to that manual. Page 7 has the details of projector mounting.


 
That was pretty much a given with ceiling projection anyway though since most projectors can't be rigged vertical.


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## ruinexplorer (Jun 22, 2011)

I disagree that it was a given. Being that some projectors are able to have full mounting positions to vertical and it was stated that the projector would be mounted off axis.


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## metti (Jun 23, 2011)

ruinexplorer said:


> I disagree that it was a given. Being that some projectors are able to have full mounting positions to vertical and it was stated that the projector would be mounted off axis.


 
Fair enough. Comment retracted.


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