Goboes or Gobos: the facts
A gobo is a thin circular plate with holes cut in it to create patterns of projected light. Opinions vary as to the derivation of the name. It may be derived from a contraction of "go between", or from "Goes Before Optics". "Go Between" means between the lamp and the lens. If you are extremely posh, or very old, or merely in the film industry, you might call it a cookie, flag or cucoloris.
There are lots of things you can do with a gobo. For some hits and tricks see my Profiles page.
The effects and that you can get from your goboes depends on a few things:
1) Quality of the lens
A good quality lens will render your image more accurately than a bad one, which can suffer from chromatic abberation and / or spherical abberation
||Chromatic aberration or "color fringing" is caused by the lens/reflector combination not focusing different wavelengths of light onto the exact same focal plane The amount of chromatic aberration depends on the quality and finish of the glass used..
2) The size of your gobo
This is quite important to get the best projection effect. see this site at LXstore for a current list.
3) The Resolution available and the maximum wattage recommended to prevent buckling and burning
a) Laser Cut goboes
Resolution: 1000 Dots per inch
Wattage: 1000 watts halogen or MSR, 400 watts discharge
Standard stainless steel
Resolution: No DPI available
Wattage: 2500 watts practical maximum:
Mesh etched goboes
Resoloution restricted to mesh size: perhaps 150 DPI
Wattage: 1200W max:
3) Silk Screened Glass:
Resolution: very high, no figures available Colour applied by hand:
no information on the life of the colour
Wattage: 600 Watts max.
A further important precaution with all glass or dichroic gobos is the insertion of a glass UV filter between the lamp and the gobo As it is UV bleaching of the pigments that causes image fading - not heat damage - this filter can extend the life of the gobo by up to 400 percent.
4) Photo Gobo
Resolution: 2500 Dots per Inch /12000-24000 DPI Hi Resolution.
Wattage 600 max.
5) Dichroic Goboes
One Colour (22 Std Colours) with clear image or 1 colour with black and white Image. Half tone is available. Wattage:600 Watts
Wattage:1500 watts maximum depending on area:
4) Life expectancy
Depending on the light source and the density of the image, the operational life of a gobo can vary between a couple of hours and indefinitely in the case of a classic metal gobo. The optimum balance between gobo life and light output is obtained by using the 575 W long-life GLA or high-output GLC lamps, checked back to 80-percent output. This is important in a architectural situation where long lamp life and gobo life are important maintenance cost considerations.
MAKING YOUR OWN GOBOS AT HOME
This is really simple, but you will never get it really looking nice by this method, it really is only suitable for very simple shapes and rough old breakups. Basically, you need a little litho plate ( ask a friendly printer for a few bits), A gobo holder of the right size to use as a template and a craft knife. You might like to pre-distort the image a bit if you are projecting it from an angle.
Cut out a piece the same size as the complete gobo holder, dont attempt to make a round one to fit in a commercial holder its more fiddly than its worth. mark the hole in the middle and draw your pattern. Dont forget that the pattern has to be UPSIDE DOWN!. Now cut it out. Thats all.'
Needs a bit of skill and chemicals, resist etc.You can buy a kit with all this stuff in it from electronics suppliers. Do your design on a transparent sheet with very black blacks. Dont leave any islands ( i.e. the middles of "o"s for example) without tagging them to a piece of land. Draw it as big as you like and then reduce it to actual size. Get some very thin stainless steel sheet, give it a good clean and spray one side with photo resist and pint the other side. Tape your artwork on and expose it to UV, develop it and etch it in Ferric Chloride. Clean it all opf properly afterwards.
Buy a £42,000 laser and some other stuff.
Now try using any bits of perforated metal, expanded metal etc that you can find.
Gobos (cookies) in the Film Industry
Cookies in the film industy create a similar effect to the theatrical gobo. They are large pieces of
board with patterns cut in them which are used to create shadowgraph effects also see Linnebach
To build your own cookie, start with a piece of 1/4-inch plywood, rigid posterboard etc. draw your pattern ( clouds, leaves, branches, window shapes etc) and cut it out with the appropriate tools. If you want to project leaves, cut a pattern with a number of small irregular shapes making sure you leave about six inches on the sides to provide support. To create clouds, cut out a number of irregular oblong shapes, leaving at least two inches of material between them. When making a leaf or cloud cookie, make sure the holes you cut out are smooth and form no noticeable pattern. You can cut out many other shapes the same way, making sure they are smooth and supported by the material left behind. You will be creating the pattern by what you don't cut out, so be careful when designing your pattern.
When the pattern is complete, you'll need to mount it to a stand and position it between your light source and your set. Now you're ready to go. Make sure you have sandbags or some other heavy object on the bottom of the stand so that it doesn't fall over. Place the cookie as close as possible to the surface you are projecting onto. The closer it is to the surface, the more defined the shadows will be. If you position the cookie close to the light source, the edges of the shadows will be very soft and washed out. If you are projecting leaves on someone's face and the background, you can have a helper move the cookie slowly back and forth to create the feeling of wind. Also known as cucoloris, cucolorus, cucaloris, kukaloris, kookaloris, cuke, coo-koo, kook, dapple sheet, ulcer, gobo.
(freely adapted from an article in http://www.videomaker.com/article/8250/
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