This is basic instructions on how to build a portable image projector that uses a green laser instead of normal light. The laser permits images to be cast great distances, and doesn't require focusing - it's always in focus.

This particular design is simple in order, more for the sake of keeping my short attention span on track for long enough to actually get this finished!

Let me know if I've missed some detail and I'll correct it.

For more photos see flickr page

Warning: Even a low power laser can cause permanent eye damage. Always wear safety glasses and never point at people, animals, or police helicopters!

Step 1: Materials and Tools

This method describes absolute basics using lesser quality optics and low power green laser.

This guide shows the set-up for slides made from overhead transparencies.

I will use the Dinkle rails and polymorph pellets.

Materials Required:

Green laser module 10mW+
1 solid length of wood (~90cm)
polymorph pellets (or a willingness to create lens holders from wood, plastic, etc)
concave and convex lens. You can get these from old disposable cameras which camera shops will throw out by the dozens.
Hardware for attaching rail to wood (bolts or screws, depending on method).

Optional Materials:

Dinkle rails, with 72mm rail modules (x4), and the mounting feet (x8), available from http://www.altronics.com.au/ (note, you may find a better way of mounting the parts, but this one works for me).
perspex or pcb 72mm with for Dinkle mounts.

Tools required:

Drill
Jigsaw or handsaw
Hole making bits for drill (if using wood to create lens holders)

NOTE:

I will use the Dinkle rails for this instruction simply because they make alignment so much easier. They also allow a great degree of modularity - being able to swap different lasers, lens, etc in and out quickly.

Step 2: Create the Base

In this method, I'm using a long plank of wood about 90cm long, 15cm wide, and 1cm thick. You pretty much mount it on any long piece of stiff material.

Note: the length will determine how much you can distance the first lens from the slide to allow the 'dot' to expand enough to cover the slide area.

Stiffness is essential. For alignment of the laser is often difficult - unnecessary flex will throw the alignment out too easily.

If using rail, rule a straight line up the centre of the plank, and mount the rail dead centre. You may need to cut the rail in order to fit it on the plank.

If not using a rail, create a centre line very accurately! Any holes drilled must also be very much in line.

Step 3: Laser and Lens

Mounting the Laser

Assuming we using a pen type laser pointer we need to mount the laser into a holder which securely hold the laser in position with no movement at all.

Since laser pointers often have a press switch, I will pull them apart and bridge a wire across the switch so that when-ever a battery is attached, it will stay on. Be careful soldering this while - you can easily dislodge other components and destroy the laser module.

Heat is often the death of lasers! Assuming it'll be on for longer than a few minutes, you may need a form of heat sink to dissipate the heat.

Find an aluminium heat sink from an old computer, and drill a hole big enough to fit the pointer into. Use thermal paste around it.

In this quick and dirty example, I'm merely pressing the laser into the centre groove with a polymorph blob.

To mount using the rail, use two 72mm perpex/pcbs'.

The bottom piece slots into the mounting block, and the other squarely above it, with bolts in each 4 corners.

This allows the vertical level to be raised up and down accurately.

Best to create this 'scaffold' before attaching any of the components to the top perspex/pcb.

Position the laser (in heat-sink) loosely on the top.

Turn the laser on and use a set square aligned along the centre line. Ensure the laser is aligned along the line, and is also exactly parallel with the plank/rail.

Once you are happy with the alignment, mark the position with a pencil.

I'll leave the method of attaching laser to you, but remember you may need to reposition it slightly later, so gluing it down now may cause regret. Some form of bolting may be better.

Step 4: The Other End

Once the laser is loosely in place, I like to position the focusing lens that sits at the other end of the rail/plank.

Use the same method of mounting the laser, to mount the focusing lens.

Use the polymorph to seat the lens - keep it centred and horizontal!

Now line up the laser so it passes dead centre through the lens, adjusting both laser and focusing lens until the beam goes through the lens and does not diverge in any other direction horizontally or vertically.

Once these two are in line, we're almost there! Just two more modules to install.

Step 5: Slide Holder

Obviously you need an image to project.

I suggest using a 35mm slide mount with either a colour slide, or an overhead transparency made to size.

Why? the denser the film, the less light can pass through. If you want to project a maximum distance, an OH image on clear transparency is the best for guerrilla art projections that require maximum illumination.

Of course, just experiment with different type of film!

As for the laser and lens, make the scaffold for the slide holder.

Using the polymorph create a slide holder simply by placing a blob, and sticking an empty mount in there. Let it set, remove mount, and instant slide holder!

Next, some tweaking of horizontal and vertical positioning of the slide and scaffold is required so that the dot of the laser is precisely centred. Don't move the laser to centre the dot!

Step 6: Spread the Dot

Using a concave lens, we expand the beam enough to cover all or most of the 35x24mm area of the slide. You can use 2 lens to expand the dot in a shorter distance, but brightness does suffer a little bit for each filter the laser has to pass through.

You can find these lens in old disposable cameras. The basic shape extrudes inwards and expands the beam.

If you want to buy some quality glass lens, then a number of reputable laser shops online can supply these.

As before set the lens within a 'holder' - using the polymorph or other materials. Set up another 'scaffold' and position the lens so that the beam of the laser passes directly through the centre.

Adjust the size of the expanded dot by moving the slide holder up and down until you're happy. This of course means moving the focusing lens too.

Once all modules are in alignment - you should see some sort of projection - if out of focus, then move the focusing lens back and forth relative to the slide to get the optimum sharpness.

A useful tool for alignment is lining up the main 'reflected' dot that will invariably occur to the centre of the preceding module element.

Step 7: Expanding the Concept

I'm sure I've omitted some important detail, but I hope its relatively clear.

There are so many ways to expand this I'm only going to suggest a few:

Use glass lens for a brighter image (pull apart old cameras for these)
Once confident, try a more powerful laser (100mW+). Remember lasers = dangerous!
Instead of slides, use small TFT screens (such as those 'digital photo-keychains'). You will need a more powerful laser though to get a brighter image. Or rip apart a digital photo frame. Caution: mobile phone screens (or any screen designed to work in sunlight) will not work nearly as well.
Use spinning/vibrating mirrors (with small motors) to create a form of scanning that potentially give the illusion of a much brighter image via persistence of vision (quite complex). This link to Starcross42's example demonstrates a technique for creating spiral effects. Check out his other videos as well!.
use biological matter between two glass slide and project the microscopic onto hospital buildings.