Lighting Gobo(s)


#1

In theatrical lighting, a gobo is a thin metal, plastic, or glass template that blocks light, allowing a pattern or image through. Like a slide in an old slide projector.

The issue is heat, which is usually too much for straight-up plastic.
Classic gobo’s are cut out of quite thin steel or other metal. Newer ones are cut onto glass. I’ve heard of acrylic being used with LED spots, but not sure if it’s a special type of plastic.

What materials could the GF cut that could be used as Gobos? I’ve heard how bad aluminum is, so aluminum foil’s out? Metal HVAC Tape? Really thin steel? Could it etch away a paint coating, but leave a clean surface below? Is there a cuttable acrylic that can handle high(er) temps?


#2

It can burn paint off a metal surface, but burning through metal is out of reach.


#3

Find a paint that you can burn off and use acid to etch the bare metal.

Or maybe cinefoil?

http://us.rosco.com/en/product/cinefoil


#4

Black Delrin maybe? Thinner of course.


#5

Hi,

I have worked in the theatres in the UK and we used to make some gobos from aluminium drink cans. We drew the design on with a sharpie and then cut them with a craft knife.

It occurred to me that you might be able to cut a different material and then use that as a template to help you cut the thin metal.

Not sure if that is helpful but hopefully it is.


#6

Would thin Corian or Delrin take the heat anyone?


#7

Perhaps acid etching or electroetchjng thin aluminum or brass.

I’m firing up my electroetching stuff today to print some Makers Mark tags.


#8

I found this page had some info about the heat in the gate are where gobos are installed: https://www.etcconnect.com/Support/Articles/Source-Four-Heat-Ratings--How-Much-Heat-Does-The-Source-Four-Emit-.aspx?LangType=1033

Looks like a range of 320-420 C

None of the plastics mentioned here would stand up to that.

Looks like etching a coating off of glass is one preferred way.


#9

I’ve worked with lighting too but very little so for the amateur dabbled that I am…what are gels made from and do they come in opaque that could be cut?


#10

Gels are by nature translucent (purpose=coloring light)
In ye olden times they were made of gelatin, hence the name.

Nowadays gel manufacturers use a variety of plastics including polyester, mylar and polycarbonate.
(Source-MFA Theatre Design)


#11

What about mylar? Reflects heat, relatively opaque, and I saw references to cutting it with GF.

Can I get reasonably thick/stiff sheets of it? What are the limits that GF can cut? I guess just try by experiment?

More general question: what is the risk of cutting something shiny, like mylar? Does putting tape on it mitigate that risk?


#12

Mylar melts at 260C, we’ll below temp of the gate location where gobos are placed for best focus. IIRC, Gels are placed outside the lamp after all the optics and are thus not subjected to as much heat.


#13

Of course, for non LED bulbs, that’s still a ton of heat at 700-1100 watts a bulb(I think that’s the range I worked with). Even if the gels don’t melt/ignite over time, they can burn off the coloring and thusly are still damaged.


#14

As an ex-“squint” I will note that even the steel gobos we used to use eventually warped and oxidized under the heat. It is seriously hot in the focal range of the gobo. I can’t think of plastics other than PTFE that could even come close to that heat. I am betting that even PEEK would sustain damage there. I mean steel has a very, very high melting point and given the amount of warping, plastic will never sustain that.


#15

A material that could be CUT by a 45W laser is unlikely to survive the heat produced in a Gobo. Even the Gels go bad over time, and they are outside the light.

I’m intrigued by the substitution of engraved glass though.


#16

Second that. I once spent much of a summer with a 1000-watt instrument that thought it was a follow spot, and when you cranked the iris down you could see the leaves glowing red.

LEDs are a huge improvement on that, but still serious heat. Maybe a mirror coating on borosilicate glass?


#17

So I’m working with 60W LED Spots. They don’t make nearly the heat of incandescent lamps. It’s the only reason I’m considering DIY gobos like this.

But apparently 60W of LED is still way too much for transparency film - it warped after only a few seconds at full brightness. Looked GREAT for a few seconds though. Wikipedia puts Polyethylene melting at 120 to 180 °C.

I don’t have a clue what sort of temps are reached in there, but I sincerely doubt it gets >250C. There’s no heat dissipation other than a fan in back, and it’s in a really tight space with rotation gears around it.

So I’m trying to find something cuttable that can handle some, but not unreasonable heat. Maybe 200C?


#18

Update, I spoke to a tech at Chauvet, and while he couldn’t find any tech specs on it, his best guess was 200-210C. So maybe mylar? Now where to source some reasonably rigid mylar…
Or is there something else that might work at those temps?


#19

Well…wood is roughly 230C for ignition so it might be workable.


#20

FWIW, McMaster has mylar in various thicknesses. But you’d really like something reflective rather than absorbing.