Don't worry, I'm not trying to sell a half finished project or one of those evil plastic TV enlarging lenses!!

I work in a small theatre as a technician operating sound and lighting equipment, and also a 35mm cinema projector. One effect common in TV and theatrical lighting is to use what is known as a 'profile spot' to project a gobo ( a metal or glass disc with a pattern or picture on it ) onto the stage. I think a profile could be used to make a simple, cheap projector.

Starting from the rear of a typical profile, we have the reflector and lamp. It is usually possible to move the lamp in relation to the reflector so that the beam from the lamp is as even as possible. Many profiles also have a condensor lens just in front of the lamp to increase light output. Lamps (DON'T CALL THEM BULBS!!! BULBS ARE WHAT YOU PLANT IN YOUR GARDEN!!!!!) range from 200 watt tungsten halogen upto 1200 watt HMI and beyond.

In front of the lamp assembly is where the gobo sits, along with shutters which can be used to control the shape of the beam. More on this later..

Next we have the lens tube, which consists of two large glass convex lenses which can be moved backwards and forwards to adjust the size and focus of the beam. Beam angles can range from 5 degrees upto 45 degrees, though each lens tube will only cover about 10-15 degrees of adjustment.

Now for the intersting bit! Rather than build a video projector entirely from scratch, if we take out the gobo and shutters and replace them with a small LCD screen, we would have a very easy to build projector. All of the hard work has already been done. The lamp, reflector and lenses are already mounted in an enclosure. The ability to zoom in and out is built in. The lenses are solid glass and not Fresnel lenses, so we wont get any artifacts from the rings associated with a Fresnel lens. If we use an ETC Source 4 Zoom, its reflector is designed to reduce transmitted infra red (i.e heat) by about 90%. Result!!

Obviously there are going to be one or two problems with this approach. The first and most important is the screen size. The biggest gobos in general use are 75mm in diameter so we could realistically only use a 75mm (3 inch) screen. We could go bigger by using a followspot which is basically an overgrown profile, but they can easily be 4 feet long or more. We could get around this by standing it on end and having a mirror at 45 degrees on top, but its still going to be quite big.

Despite these problems, I think building a projector using a profile would be an excellent introduction to DIY projectors. The cost of the parts isn't going to be astronomical if you buy them secondhand. I am in the process of getting all the parts together to build my own projector. I've found a portable LCD tv on ebay, and I know some places where I can get profiles from quite cheaply. Altogether I think this project will cost me no more than £100 or so, probably less. I'll let you all know how I get on but don't expect any major developments soon as I am currently moving house :-)

If you want to build your own, look for a profile of around 1000-1200 watts as these have bigger lenses and can take the largest gobos. You could always fit a lower wattage lamp if you need to. Names to look out for are ADB, ETC Source 4 Zoom, Strand Cantata, Robert Juliat ( if you want to use a folowspot ), CCT Freedom.

For who has not the same technical knowledge you do in the theatrical lighting field I think is a little tough to understand what you are talking about... so we'll probably stick with this project although it requires to do all the hard work to start from scratch

What you say sounds interesting indeed and if you could post more details about it it may also help us getting more ideas to develop further the lumenlab projector. If you have any images of the equipment you are talking about please post them here so we can get an idea of what the hardware looks like.

thanks

Not going to get a small LCD (<7") with decent specs for anything less than $1000.

This guy made the exact same post at DIYaudio.Why is he doing this here too?

Hummmm, I to know about theater fixtures and what he is saying is right. But like Brainchild said it could cost so much more for a 3" LCD why not DLP?

But I wonder about the lens and the zoom. Humm will have to hunt down a zoom fixture. I only have the standard kind. Be fun to test.

well I cant see how it can be consifered ready made when you still need to construct the hard 90%.

as for why he posted on both forum's.... he either thinks he has a good idea and is being nice.... or has an excess of the brand names he lists he needs to ofload