# projector lumen and focus newbie questions



## pguar (Jul 9, 2016)

Hi,
I would like to do a projection on a big 16:9 screen 10 meters wide (about 33 feet)... What is the ideal ansi lumen should I look for... And what about a minimum (low budget) setup?
Is there a big difference if the screen would be 8 meters (about 26 feet)?

About projectors... I see there's often a minimum focus distance on the projector specs... And then there's Is there also a maximum focus distance should I look for? In other words... Can I put my projector at any distance from the screen and the image will still be on focus?


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## MNicolai (Jul 9, 2016)

16:9, 30' wide, you're looking at 12K lumens give or take.

Having just sold a projector for that size screen yesterday, I can tell you it's about ~$20K to buy that size of projector w/ lens. 

Projectors of this caliber have interchangeable lenses. You get the lens that has the correct zoom ratio for how far your throw from the projector to the screen is.

Price wise, negligible difference between 26' and 33' ft, but since you said low budget, I expect the smallest you can go the better because if you try to do this with a 8K lumen projector you'll need a smaller image area to get a brighter image, and you'll be far stretching the capabilities of that size projector to show an image that large.


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## ruinexplorer (Jul 10, 2016)

This isn't as simple as a one size fits all. There are variables such as the screen type, the content, and the control of ambient light. All of these will affect the quality of your image. Reducing the size of your image will grant more lumens per square meter. For cinema, you should have 16 lumens per square foot. Theater applications often require much more. There is not a standard for theater, but I generally push for at least 25 lumens per square foot.

As for lensing, yes, you can run into maximum throw. Your image will be a result of the throw ratio of the lens. On zoom lenses, you can exceed the point at which you can effectively focus the image. However, you will likely not reach that as your image would also be too large.


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## pguar (Jul 10, 2016)

I will use a front projection on a white projection screen with 1.0 gain, wide lens (0.8:1). There won't be ambient light, actors will be some meters ahead of the screen lit by zoom profiles to avoid unwanted light hitting the screen and shadows from the actor.
I'm very confused about the projector because someone is advising me on using something in the 10K - 15K range but there's someone else telling me that there's no reason to use so much power and I can do it with a 4K / 5K ansi lumen or so if I have no ambient light or light hitting the screen...


I'm asking about the focus because I'm planning to use a short throw projector for another application that is rated to project from 0.4 - 3.6 meters on projectorcentral but I need a bigger image (it's white text on black background so I don't need it to be very bright) and I would like to project from 4.8 meters but I can't guess if the projector will focus the image from that distance...


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## ruinexplorer (Jul 10, 2016)

If you could absolutely keep all light off of the screen, which would be near impossible as you light the rest of the stage, you could get acceptable cinema levels with a 10,000 lumen projector with the 10m wide screen. You would need approximately 15,000 lumens for a good image for live performance.

For the 8m wide screen, you would only need about 6,500 lumens for cinema and 9,500 lumens for live performance. This is due to the area of the screen being smaller. 

Part of your target goal is to have the best contrast ratio possible. In live entertainment, we understand that there will be some ambient light, that's just the way it is. So we go for a brighter overall image to compensate for the ambient light. It only takes a couple lumens (literally around two lumens) to begin to wash out your image if you don't have enough light from the projector. It's good that you are using an actual screen and not theatrical fabric which would have an unknown gain.

As for the focus, if you are only looking at text, you should be fine with a plain font at a large enough point to keep it legible, even if you go beyond the normal focal range of the projector. We have a remarkable ability to look at recognizable objects and either see every flaw or fill in the details. When it is something like text, which is recognizable, we will notice the flaw (that it might be slightly out of focus). However, we won't mind so much due to the distance between the screen and the audience. As long as the text is large enough, no one will notice, even the trained professional.


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