Custom glass gobo installation which side to lamp?

JChenault

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Jan 5, 2009
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seattle, wa USA
i have a custom glass gobo I am reusing from a prior production. One side is the glass, and the custom part appears to be deposited ( painted or printed) on the other side. The two sides are clearly different ( I think this was a Rosco gobo, but I am not at all sure)

Which side wants go towards the lamp? The clear glass side or the printed on side?

Thanks in advance
 
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derekleffew

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Does "upside down and backwards" not apply?
"So the lamp can read it?"
Is it going into a "moving light," SourceFour, or 360Q?


I do hope @GreyWyvern is within earshot.
 
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GreyWyvern

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Fort Wayne, IN
Not really being a lightning person and having only used metal when I have been coerced into it, I don't know much about gobos. I do know "upsidedown and backwards" when it matters. On some glass gobos, side matters, but others don't. Hopefully @Kelite is within earshot to help out.
 

RonaldBeal

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TN
The irony is that while that link says "Multi Layer glass gobos should always have the dichroic layers of glass installed away from the lamp" when I worked for Vari-Lite, they said the exact opposite for their gobos in VL-2s and VL6s (gobos manufactured in house). Certainly, I am sure there are differences in manufacturing between the different gobos, but goes down to "what does the manufacturer recommend?"

The reason I was given for coated side towards lamp, is that the coating reflected not just visible light but IR and UV, and having that on the lamp side reduced the thermal heating of the glass, where as having it reversed meant that a lot of that energy passed through the glass twice, (once on the way in, and again being reflected out) so impurities in the glass absorbed more heat.

Just my recollections.
RB
 
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JChenault

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seattle, wa USA
Upside down and backewards does not help in this case ( it is semetrical right to left ). It goes into a moving light ( revolution )

For now I am putting the “ printed” side away from the lamp

As the gag is only up for work 20 seconds or so it is probably not a big deal
 

Kelite

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Fort Wayne IN, USA
Hi guys!
Depending upon the manufacturer of the glass pattern as well as the age, processes have stayed fairly consistent over the years. As Ronald Beal pointed out:

"The reason I was given for coated side towards lamp, is that the coating reflected not just visible light but IR and UV, and having that on the lamp side reduced the thermal heating of the glass"

Reflecting heat energy is a plus for any medium in a lighting fixture, whether that be a glass gobo or a gelstring in a color scroller. The rule of thumb with b/w and colored glass is placing the most reflective surface toward the light source, darker away. Being able to redirect IR and UV back at the reflector (glass reflector, hopefully) to keep the gobo cooler is the plan. Placing the darker side towards the lens also minimizes reflection ands halo.

JC, is there a shinier side to your glass gobo?
 

SS Minnow

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Jul 8, 2016
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USA
I was once taught that a gobo image flips every time it passes through a lens, which technically means that you would have to know how many lenses you are passing the image through, depending on the fixture, to know which side needs to be toward the lamp which would also determine which side of the gobo gets coated. This of course would really only be crucial for gobos with text and branding, not so much for a breakup pattern... Just sayin'...
 

JChenault

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Jan 5, 2009
Location
seattle, wa USA
Hi guys!
Depending upon the manufacturer of the glass pattern as well as the age, processes have stayed fairly consistent over the years. As Ronald Beal pointed out:

"The reason I was given for coated side towards lamp, is that the coating reflected not just visible light but IR and UV, and having that on the lamp side reduced the thermal heating of the glass"

Reflecting heat energy is a plus for any medium in a lighting fixture, whether that be a glass gobo or a gelstring in a color scroller. The rule of thumb with b/w and colored glass is placing the most reflective surface toward the light source, darker away. Being able to redirect IR and UV back at the reflector (glass reflector, hopefully) to keep the gobo cooler is the plan. Placing the darker side towards the lens also minimizes reflection ands halo.

JC, is there a shinier side to your glass gobo?
The shinier side / more reflective side is the one which has no pigment/dye on the surface. It is facing the lamp / reflector at this time
 
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derekleffew

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I was once taught that a gobo image flips every time it passes through a lens, which technically means that you would have to know how many lenses you are passing the image through, depending on the fixture, ...
SourceFour 19°, 26°, & 50° have one lenses. SourceFour 36° has two. Gobo with text goes the same way in all.
Myth busted.
 
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