Replies to This Discussion

Permalink Reply by Florian Canga on February 24, 2014 at 2:43am

Hi.

I have experience for projections in theatre.

Usually use wide angle lenses 0.8 fixed zoom for rear projection and frond to.

Use balcony for overhead projection

use format 4x3 or 5x4 because u have also hightnees of image

use silent projectors ( panasonic are mos silent or LAser projector from Digital projection)

thats in general. vsdproject.com

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Permalink Reply by Rick Reid on February 24, 2014 at 8:14am

Beware of spill light!

Any stray light from stage lights to exit lights will reduce the sharpness of the images, no matter where either screen or light are located. Also note that most LED fixtures have a larger percentage of spill than traditional units. So stock up on top-hats, barndoors and the like.

And make sure the stage area is black to absorb as much of that spill as possible.

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Permalink Reply by Erich Friend on February 24, 2014 at 10:08am

For rear projection, the screen surface is very critical. It must be very diffuse or you will see an image hotspot on-axis of the projector. Wide angle lenses tend to exacerbate this problem.

For front projection, the surface of the screen must match the location of the projector - off-axis light rejecting screens must have the projector on-axis, which is not always practical. If you are projecting from a steep angle (i.e. using significant lens shift), then a screen surface that is more omni-directional may be needed.

Figure-out the screen size, know the screen gain, determine where the projector should be to not interfere with the operations or audience, then select the lens you need to do this. Longer throw lenses loose more light, so you have to account for that when calculating the amount of lumens needed from the projector. Projector manufacturers only tell you how bright their projectors are with the most efficient lens, so you have to add the long-throw lens loss to the equation (this requires an understanding of f-stops). From this , you can figure-out how bright of a projector to rent / buy.

Know if you are trying to make one big image from a single projector, or from multiple stacked projectors, or are you tiling together several images and doing edge-blending. All of these have cost, space, and hassle-factor implications. In spaces where there is limited space from the screen to the rear wall, you may need to fold the image with mirrors. More expense, hassle, and knowledge required.

Also in the calculation you should consider the contrast ratio goals you are trying to achieve. How much wash-out is acceptable for your application?

Don't get the horse before the cart and expect a low brightness projector to provide a large vibrant image. Once you think you have it figured-out, get a demo before you buy to determine if your proposed solution will really get the job done. This applies to screens as well as projectors.

Contact me directly if there is something specific we can help with. I'll be coming your way in June.

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Permalink Reply by Ed Gilmartin on February 24, 2014 at 4:59pm

Erich,

Thanks very much for the comprehensive reply. We are doing a showroom visit to see some projectors this week.

It's clear that there is a lot of knowledge to be acquired in making these decisions. I'll drop you a line as things progress.

What's bringing you to Tokyo in June? (egilmartin@asij.ac.jp)

All the best,

Ed

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Permalink Reply by Nathan Kelley on February 24, 2014 at 8:40pm

If you happen to be referring to projecting images onto a cyc at the back of the stage (instead of using backdrops) here is my advice. There are pictures on my profile of some musicals where we do this.

There are a lot of variables here (projectors, lenses, bouncing off a mirror, amount of space behind the cyc...) If you are doing rear projection you'll need quite at bit of space behind the cyc unless you can afford some high powered projectors and bounce it (them) off of mirrors.

I use a pair of Benq MX620ST XGA projectors mounted in front of the cyc roughly 13 feet away. Using a Matrox dual head-2-go video interface to span the image across the projectors this gets me a 35' x 12' image on the cyc. This fits our cyc perfectly. This is the most cost effective way to do this. We use ProPresenter v5 to deliver the images/video.

If I had money I would buy one WXGA or 1080p 10000 lumen large venue projector with the appropriate short-throw lens and still project from the front.

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Permalink Reply by Ed Gilmartin on February 25, 2014 at 1:12am

Nathan,

Excelling information, going to look into all you have given me. Thanks a ton!

Ed

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