What he said. Get a long lens.
Originally Posted by Lee L
Most modern outdoor projection equipment is, of course, digital. This would be a rather pricey rental item, try A/V rental firms.
You might be able to get by with an auditorium projector: if you only need it for a short time, and can put an educational/arty-farty slant to your usage, you may be able to borrow a few from a local university. Also try A/V firms, a big one might have some available for not that much money. These things normally take 3x4" (whatever the standard size) glass mounted slides. Using these with color transparency materials may be problematic as the light intensity in these things is fierce. Color ink-jet on mylar film might work.
Your second problem is 'the side of a concrete building'. You will need an outdoor projection screen, trying to project on concrete isn't going to work very well. Outdoor screens can be rented. You can make one from Tyvek and screen paint, or you can paint the side of the building with either screen paint or the best white titanium paint you can find.
Thanks Nicholas but unfortunately, a screen is not an option as i'm projecting onto the walls of a high building.
Your note about protecting the slide is also a main concern - I plan to leave the projectors on all night (or at least for 4-5 hours straight). Do you think ink-jet on mylar film will be able to cut it?
You could get an extra bright lamp modual for an Ektagraphic or even one of those very, very high power xenon units put out by NOVA as far as I know. Plus the proper lens. You'd be all set.
I have a Beseler Slide King, and they do project a beautiful image, though I haven't tried projecting on a surface as large as the side of the building. The one I have was used in an auditorium. There are wider lenses, but they're hard to find. I've picked up a lens or two and some slide carriers from a place that specialized in them. The projectors are usually fairly cheap on eBay, but the accessories can be a little pricey in comparison.
Bear in mind that you may have to make custom mounts for your slides with a Slide King, since carriers for standard sized mounts can be hard to find, but once you've narrowed down the images in your show, it's not so hard. You can cut them from mat board like little window mattes.
It is also a totally manual projector like in old movies--insert slide, move carrier, remove old slide, insert new slide, and then move the carrier back to the previous position.
There are many specialty projectors made for exactly these types of applications, but even they are only so bright. Typically, when very high brightness is required, multiple projectors are stacked, each projecting the exact same image on to the same screen, with the optics adjusted to bring the images into register. I'm not sure if this is possible with ordinary slide projectors, as you need to be able to shift the lenses.
If the Slide King cant do it I dont know what can. They dont call it the Slide King for nothing. That thing comes in a metal box that looks like a rocket launcher case.
For your interest, the throw in my little venue at work here is 15.5 metres from projection room to screen, and our fancy new HD projector needed a lens upgrade for that. At 6000 lumens, and with the longer focal length, it projects a 2.5m x 4.44m (16:9) picture really brightly. The 16mm Kinoton here has a 45mm f/2 lens for the same throw with a 1.2kW lamp, and is also very bright.
It has been interesting looking at some of the fancy new projector installations in lecture theatres here - one I looked at yesterday had a 4 lamp DLP projector installed (ceiling mounted, really close to the screen), just to compete with the GIANT west-facing window running the length of one side of the space. Technology battles architecture...
Distance is irrelevant, it's magnification that matters for power/brightness, i.e. image size. For the side of a building and decent brightness, you need a thousand watts or three. You get the same effect from a short lens up close as a long lens further away as long as their relative aperture is the same.
As choosing the focal length, it's a function of your slide size and how far away you want the projector. Same geometry as with a camera.
There are occasional events where people project patterns on whole buildings and that particular one is done 5kW lamps shining through 5" mylar rolls that advance every two minutes; I think the image is around the 5x7" size. They're 4-story-high images though and projected onto dull sandstone - if your building is white or concrete, you will get better brightness.
I would suggest you look at getting something at least as grunty as a Goetschmann G67 (it's like a Slide King but more modern; takes the 85mm mounts). 35mm WILL NOT cut it because the optical flux through the slide required to light up a building will melt it. If you wanted to hack a Slide King or similar for wide angle, you could start by mounting shorter RB or RZ lenses to the front.
Of course you can get a digital projector to do it, but you're talking about a cinema-class Barco for many tens of $k, not a powerpoint-thrower designed for office use.