Tales of Experimental Photography
Disclaimer: The author of this guide is not liable nor will he take any responsibility for any direct or indirect accident that might happen as a result of anybody building or operating the installations described. It’s every builders own responsibility to make it safe! Please read my remarks on laser safety before doing anything.
The probably simplest approach to create a light plane is using laser diodes with line generation optics. These can be purchased on the Internet as so called “Line Laser Modules” and are relatively cheap. These modules mainly differ in wave length (color), power output, quality of the optics, fan angle, module size and input voltage requirements. Additionally better modules have an adjustable focus (the focus sets where the line is sharpest, not required for LPP but of advantage). You are looking at something between 20 and 200 US$ each, depending on the color, quality and output power. Google for “Laser Modules” and choose a seller. Line laser modules are also available on eBay. I have never seen this kind of laser modules in any conventional shop. But you probably could disassemble alignment devices sold in hardware stores which use line lasers. This would be a rough hack and I suspect the output power of these diodes won’t be enough for anything but a very simple plane, but it might work.
For a basic setup you need two line laser modules. One works too but you will have very basic results and objects will only be illuminated from one side. I’ve done some pretty impressive pictures with just one module but these were RGB modules with 250mW output power, that’s far beyond a basic installation.You can also start working with three, four or more modules but the setup will be more demanding and you will need to construct some sort of attachment more complex than described here.
The laser modules have to be powered according to specs, usually batteries or simple power adapters, check the specs of your modules or ask the seller. The cheapest option would be red (650nm) modules with 5mW output power, plastic Fresnel lens and 90 degree fan angle. A more expensive option which would result in better optical quality and more detailed pictures: Green (532nm) modules with 5mW output power, spherical glass lens and 120 degree fan angle.
It’s strongly advised not to use laser modules with more than 5mW output power unless you are very sure of what you are doing. I was using four 5mW green laser modules for a long time with fantastic results. If you opt for green DPSS lasers, make sure they have built-in IR-filters, even at 5mW! Read my remarks on laser safety.
You’ll need something to attach the laser modules to, for example two tripods, but two chairs or a door frame can do the job. As the modules need to be aligned, you need some sort of flexible attachment for them. This can be small ball heads as used for lightening equipment or flexible tripods for point and shoot cameras. The laser modules themselves can be attached using cable ties or gaffer tape to the ball head or tripod. In worst case use tape and fantasy.
The installation should be inside a dark environment. Any additional light or stray light from the lasers will result in (mostly) unwanted ghost images of your model on the photos. Stray light from the lasers can be reduced using black cloths to cover reflections from walls, floor and ceiling. You probably won’t have any problems with stray light if using 2 red lasers. Green lasers are more of a problem, four 5mW lasers can create enough stray light to be visible even with shorter exposure times. The less unwanted light you have the better the results will be. It should be sufficient for a first test if you shoot at night and simply switch off all lights, at least as long as there’s not too much light coming from outside. It will also help if you use a black cloth or back-drop as a background.
Alternatively, the whole setup could be installed outside during the night, e.g. using trees as attachments for the lasers. Also, anything visible in the background or foreground of the image might actually be desired, e.g. if you want to take pictures of the green ghosts haunting your house or simply mix traditional photography with LPP.
The laser modules are positioned opposite of each other. The distance depends on the space you have available, anything wider than the object (or body) you want take images of is OK. You don’t want the installation to be too wide though, as the wider the light plane is the less bright it will be at the center. Align the two laser planes so that they overlap as exactly as possible. To test your alignment, put your finger into the laser plane and make sure you see one nice, round ring around your finger. Try at multiple locations in the plane.
You need a camera that supports long time exposure, ideally in bulb mode, and manual focus. That’s the only requirements. Using a digital camera will make things much easier, especially at the beginning before you get the hang of it. But it’s not a requirement, there’s no reason why not to use film. Film would even be an advantage as film is more tolerant if you don’t get the exposure exactly right. Also film is better at long time exposures (no noise, no dead pixels).
Any decent DSLR or EVIL camera will do the job, some advanced point and shoot cameras can also be used. If you have an app that supports long time exposure you could even use your smart phone. But be prepared for the need to use high ISO, especially if you use low power laser modules. Red laser modules also tend to require higher ISO as camera sensors are less sensitive to red light than they are to green. But, an alternative to high ISO is always slow subject movement, there’s no need for high power laser modules.
Put the camera on a tripod or some other sort of support, align it perpendicularly to the light plane. The distance from the camera to the laser plane depends on the focal length used and the desired frame size, choose accordingly.
Switch the camera into manual focus mode and focus on the light plane, you can use an object which is placed so that it just touches the light from behind. Or ask your model to stand in the light. Make sure the camera is as exactly perpendicular as possible to the light plane, otherwise parts of the pictures might be out of focus. Set the aperture to the lowest number you feel comfortable with, depending on your lens and how exactly you were able to adjust the camera orientation.
You will need to experiment with ISO settings. The ISO sensitivity will, together with the speed of your movement through the light plane, determine the brightness of your result. Too low ISO (or too fast movement) and the image is too dark, too high ISO (or too slow movement) and you’ll have a picture of a white blob.
Finally, switch the camera to bulb mode or choose a long exposure time, e.g. 10 seconds. Start the exposure and “draw” the picture with the light from the lasers using your hands, feet, body or any object of your choice – you should have a decent results immediately!
Here’s two examples what moving through a simple red light plane looks like:
If your picture does not show the desired effect try to analyze what went wrong from looking at it. Most probably your exposure is too dark, so increase ISO or move slower. If you can see the background you will need to decrease overall exposure or eliminate ambient and stray light. If your image is out of focus, check the alignment of the camera and the focus, make sure your camera is not auto-focusing.
If you mix traditional photography and LPP you will need to figure out the exposure somehow, that might be tricky. Consider using gray filters or try long exposure time in combination with a manually triggered flash. Which technique exactly to use depends on your specific installation and environment.