# How do I do this?



## jcslighting (Mar 19, 2017)

I am in the planning stages for a production this summer. We are using a venue with 2 installed projectors, one on each side of the stage. We want to use both projectors to cover a drop that will be hung onstage. The angle will be close to 50deg from ctr on each side so approx 100deg between them. Currently the projectors are cabled to a switcher in the booth with hdmi cables.

I was thinking of using qlab as their software will handle the extreme keystone correction easily from that angle and I don't think the projector's keystone will come close. This will require 2 different 'screen' set-ups in qlab - how can I do this? Can I do this? Is there an easier way to do this? Any advice or suggestions are greatly appreciated!

Thanks in advance!


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## Tamas Nagy (Mar 19, 2017)

I think this is totally possible - probably in any video playback software that supports corner pinning/keystoning. I'm not sure how you can do that in QLab but I bet that is just a few clicks.


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## JimmyM (Mar 19, 2017)

https://figure53.com/docs/qlab/v3/video/surfaces/

This should help you out, in QLab, you can edit the surfaces to achieve what you are trying to accomplish.

Also, I can't help but ask how long are the HDMI cable runs, I assume the setup works as is, but usually you can't go further than 30-35 feet without a signal repeater, VGA or SDI usually is a better solution for long runs of video.


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## ruinexplorer (Mar 19, 2017)

Remember that when you are dealing with extreme keystone, you are not just dealing with fixing the geometry. You are also going beyond the focal plane of the image (only part will be in focus) and you are losing a lot of lumens in the area you are correcting.


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## JimmyM (Mar 19, 2017)

How are the existing projectors installed, if it isnt too much of a hassle, I would see about repositioning so they are more direct before you start keystoning them. That will help loads when trying to make them look decent, maybe some pictures of the space could help? Im just looking at this from someone who's done a little with projection, and have them both facing perpendicular to the screen, so I'm sure someone will give you better advice, but that's what I would start by doing before you start messing with the "lossy" world of keystones


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## TNasty (Mar 20, 2017)

Having dealt with projection both in school installations (from summer apprenticeships) and in theatrical installations, I've got a pretty good deal of experience with hanging projectors. There's several things you can do to make this task a lot easier. One would be that most manufactures have their manuals on their sites, sometimes they include the projector's maximum keystone. Second, you should see your mounting options, you may or may not be able to find something that will reduce the current angle you're talking about. Thirdly, you should make sure that the projector can operate in a "ceiling" or "top-front" mode, since you'll probably have the units hanging upside-down. Finally, plan how long your cables need to be (not just video, but also power). You can get some baluns to make your video run a lot easier and potentially cheaper using Cat5e.


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## Chris15 (Mar 20, 2017)

Because of the geometry issues that mess with the focal plane, I would expect the near side to be noticeably brighter than the more distant side...


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## TNasty (Mar 20, 2017)

Chris15 said:


> Because of the geometry issues that mess with the focal plane, I would expect the near side to be noticeably brighter than the more distant side...


That's pretty much correct. Although, it could work fine if there's light leakage from lights over the stage (which would likely hit the top of the cyc).


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## Chris15 (Mar 20, 2017)

One could probably also correct for it by grading the digital image brightness to counter the optical losses...


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## ruinexplorer (Mar 20, 2017)

Yes, it is possible to even out the image, but it may be more work than the end result is worth. It would also be best to build the content with the opposite keystone so that when it is projected, there will be less loss of information in the digital correction for the keystone. 

The other option, if possible, is to overshoot (make the image bigger) and thus having less need to keystone. You will have a more even image and it is going to be easier to match the images, even though you are still losing pixels.

My question is, are the projectors normally putting an image on either side of the proscenium and that is why they are so far apart?


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## jcslighting (Mar 20, 2017)

Ok, a little more info about the venue. It is and event & wedding venue with a 30x14 stage platform and video screens on either side of that stage that are permanent installs. For theatre we use the existing stage but add onto it and build in a false proscenium. The total width from projector to projector is approximately 70' or each is about 30-35' from the centerline and approximately 14' DS of the false proscenium. I am not sure the venue will allow us to remove and physically remount the projectors but they would most likely be ok if we just refocused them. 

The false proscenium and masking walls are extending beyond the existing projector screens and therefore make the projectors un-useable in their present configuration. We are doing "Wizard of Oz" this summer and I was hoping to use the projectors for simple scenic projections with actors in front of but not directly in front of the projection drop. I have used a front/flat 10000lumen projector at a local high school with no problems but these are 2-5000 lumen units. I realize that the intensity will be less and I'm just trying to see it this is possible or should I contact the venue about moving the projectors for the show and them putting them back. There is a control booth on the 2nd floor across from the stage about 40' or so from the projection surface - that would be the 2nd option if they allow us to move them. 

Thanks for the suggestions and advice so far!


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## ruinexplorer (Mar 23, 2017)

Ah, kind of what I was thinking. With the false proscenium and the projectors being that far off of center I think that you have the added challenge of shooting to the opposite side of the stage. The upside is that you have the non-keystoned image to align. If your imagery is much more organic, you might not have to worry about correcting the image much at all. Obviously, getting to move the projectors is the best option, but you still have some things to work with.


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