Just how fast should a gobo burn out?

[EdSavoie]

Hi all!

Been awhile since I've been around on here, wasn't really working in the industry for over two years (I suppose the same as most of you....) But by the time I was working again, it didn't stop long enough for me get back on here!

While there's a general understanding that gobos are a consumable, which, you know, is to be expected unless you're lucky enough to be entirely moved to LED (Or, frankly, entirely Source Fours. Believe me, I'd love to be rid of these very well worn Colortran Lekos)

I'm reasonably sure steel gobos aren't supposed to be blackened and have parts burnt / melted away within thirty seconds.
I mean, really fine foliage breakups I expect to get rather crispy after a few rounds with a 1000W FEL in a Colortran leko, but this is a bit more extreme than that.

I'd upload a photo, but this is for a production of The Sound Of Music, and you can probably guess why I might hesitate to upload an image involving a certain symbol. (And also why someone would order these custom.)

The major clue I have is that these are custom ordered gobos, and appear to have what i can only describe as an anodized orange coating. I should be able to grab another example of a custom gobo from the same supplier.
These are untorched, which doesn't surprise me given that these ones are on our balcony rail, which is one of the few positions that is entirely populated with Source Fours. (With 575W lamps to boot.)

Am I barking up the wrong tree?
Adjusting the position of the lamp within the reflector didn't appear to have much effect...

PS: We're actively trying to justify getting the budget to be rid of these colortrans and their even older Strand counterparts we still have in our FOH and cove positions, we inherited enough S4 Juniors to be rid of all the onstage colortrans, so we're hoping to either directly acquire new LED lekos from ETC, or potentially buying a few more used full size S4 bodies and some lens swap kits with them newfangled Source 4WRD II retrofits... But we're not quite there yet.

 

[egilson1]

I would check to make sure that the fixtures are tuned properly. This will make sure that the focal point isn’t at the same location as the Gobo, which if it is, concentrates the heat at that one point and would shorten the life of the Gobo.

 

[almorton]

Yes, something's amiss - we've got steel foliage gobos that have done many years in 1kW fixtures without damage. Discolouration, sure. Damage, no.

 

[derekleffew]

From a ride in a theme park. I believe just over two years of 16/7 operation.

Strand LEKO with 1000w FEL lamp.

Use a gobo or shutters?

I need to get a very narrow beam out of a S4 ellipsoidal. Focus isn't the issue, just need a very narrow box. Do I shutter it in, or use a variation of Apollo Design | Rectangle (even that one might be too wide). It'll be gelled to a very dark color, like a primary red, blue, etc.

www.controlbooth.com

 

[EdSavoie]

As an update, I've heard back down the chain the following that apparently came from the manufacturer.

"Special Note: We do not produce metal or glass gobos for older fixtures, such as the Altman 360Q, Altman 3.5, and Colortran 5-50, or other fixture equipped with over 800W halogen lamp."

Womp womp. I guess that might explain part of it.

Yes, something's amiss - we've got steel foliage gobos that have done many years in 1kW fixtures without damage. Discolouration, sure. Damage, no.

For sure. We have loads of gobo inventory from apollo and rosco that have been through many cycles in Colortran 5-50s. Until *very* recently, they were the only Ellipsoidal we had in any major capacity since the last major theatre overhaul in 1991.

Poor lekos have taken their fair share of thermal cycles, lamp detonations, god knows how many lineset bumps (The tips anyway, courtesy of 9" centered fly pipe spacing). The usual cause of death for "normal" gobos in those tend to be warping, and then catching another part of the fixture on the way out.

After a bit more digging in the control booth archives:

I have used the 5/50s many times for Gobos and I can confirm what Derek has said the use of a Donut will improve the sharpness. Another trick to improve the sharpness is to use a GLC lamp instead of the FEL and make sure the fixture is correctly bench focussed. You will also find you need to keep the dimmer in the 50% to 70% range otherwise the gobo will become so hot it becomes cherry red and acts as a second light source which is a common reason the image becomes fuzzy.

Well I didn't think they got that hot



Didn't get a chance to grab a photo of what these custom gobos look like for reference, I'll try and get one tomorrow.
Pretty sure they're being bought through Sunhope out of toronto, who runs the website that has that warning plastered repeatedly throughout. Can't say for certain, I'm just the guy who got handed the gobos, lol.

 

[Kelite]

Stainless steel alloy and thickness is key here. Most catalog gobos from the 'other guys' are .005 inches thick and made of 400 series stainless steel. Apollo uses .008 inch thick 300 series stainless steel with higher nickel and chromium content. No rusting or burning since 1992.

You get what you pay for...