Glass gobos and 360Q not friends?

[CrazyTechie]

So for our production of Equus at my college I was given the task of ME. Well the light plot called for some glass gobos to be used in some 360Q 6x9's. It wasn't too long into rehearsals we started having some problems with the gobos falling apart like so:


So my question is, why does this happen in a 360Q but not in a S4? All the ones in the S4s were still in perfect condition when I took them out to put away today.

[derekleffew]

Rosco Gobos - Fixture Size Chart

[CrazyTechie]

Thanks for that information, I'm sure it will come in handy.
Here is the link for the same chart but with ETC's lights Rosco Gobos - Fixture Size Chart.

I'd still like to know what causes the gobo to break apart in the fixture if anyone knows.

Thanks.

[Les]

It's because the 360Q has an Alzak aluminum reflector which transmits a lot more heat through the beam than the glass Dichroic reflector found in a Source Four. The Dichroic reflector passes heat through the rear of the fixture, while the aluminum reflector throws it forward and through the gate. This causes the 360Q gate to get way hotter than the glass gobo is designed to handle, in turn, breaking it apart. I've also seen the rear lens in a 6x9 crack in a Y formation, and I've even pulled a gobo out of a poorly bench focused 6x12 to find that it is red hot.

It's too bad your professor apparently hasn't covered this in class.

[jglodeklights]

Ditto on what Les said. To expand on what was already said about Dichroic reflectors, how they work is by acting as a cut-off filter. If you've ever done infrared photography, you know that generally you utilize a lens filter that allows only infrared light to pass through it. Unlike that filter which simply absorbs non-IR spectrum light waves, Dichroic reflectors shove it out the front of the lighting unit. Not only are they used in more current fixtures, but every MR-16 lamp is comprised of the lamp and a Dichroic reflector around it.

Also worth mentioning is the transmission efficiency of the lens train in a 360Q. S4 units use thinner, more pure glass and thus; especially those with 19, 26 and 50 degree lens tubes mounted because they only have one lens versus two; allow more light to pass through without it being blocked or reflected back into the unit. Physics dictates that energy has to go somewhere, and if light isn't going out the front of the unit then it is turning into heat within it.

[Lotos]

I'm late to the party, and can't really add much... But, to test this yourself, the following experiment is handy:

Plug in a Source 4 and an Altman 360Q in a convenient to reach location.
Lamp them both roughly the same.
IE: 575w HPL in the S4, and a GLC or and old HP600 in the Altman.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

[jglodeklights]

I'm late to the party, and can't really add much... But, to test this yourself, the following experiment is handy:

Plug in a Source 4 and an Altman 360Q in a convenient to reach location.
Lamp them both roughly the same.
IE: 575w HPL in the S4, and a GLC or and old HP600 in the Altman.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

Maybe getting two thermometers rather than using your hand would be wise.......

[Lotos]

Maybe getting two thermometers rather than using your hand would be wise.......

Oh that's just crazy talk

[CrazyTechie]

It's too bad your professor apparently hasn't covered this in class.

Our TD who is also our LD knew that this might happen but we were out of S4's so he had to go with the 360Q's. Thanks for the explanation it really helps and is something I haven't learned yet in the very few amount of theatre classes I've taken so far.

Turn them on for 15-20 minutes or so, then go up and (gently... You want to keep your skin here) touch the sides of the barrel's on both...

Maybe getting two thermometers rather than using your hand would be wise.......

Not a bad idea to test out, unfortunately I don't think I have a thermometer lying around to use. Good thing I have ten fingers, I think I can sacrifice one or two for the sake of knowledge and still be able to work.

[jglodeklights]

Oh, you won't be sacrificing your fingers.....just your fingerprints!

[Lotos]

Oh, you won't be sacrificing your fingers.....just your fingerprints!

Never trust a lighting technician who still has recognizeable fingerprints...
Or is it the other way around? I can never remember...

[CrazyTechie]

So today the costumes and makeup class came in to see makeup under stage lights and I was able to find a 360Q and a S4 that had been on for a while and I touched both of them. Well the 360Q was much hotter than the S4 so now the reasoning behind all of this is starting to make sense.

[derekleffew]

From KnowledgeBase: Source Four Heat Ratings/ How Much Heat Does the Source 4 Emit? - Electronic Theatre Controls :

What is the Gate Temperature of a Source Four ERS?
In a test condition created by placing one shutter blade into gate covering 1/2 of field, and
placing the thermal probe on the backside (shaded) of the shutter, the maximum S4 gate temps
(A-size) were recorded as follows:

HPL 575w/115v/300hr = 622°F
HPL 750w/115v/300hr = 786°F

Anyone wanna stick a thermal probe in a 360Q and post the results?

[Lotos]

Out of curiosity, now that I think about it...
You didn't do something silly like put FEL's in those Altmam 360Q's as well, did you?

Not that the GLC will be gentle and kind to the Gobo's... But FEL's are notorious heat monsters.

[CrazyTechie]

Out of curiosity, now that I think about it...
You didn't do something silly like put FEL's in those Altmam 360Q's as well, did you?.

Heavens no. I've never heard anything but bad about FEL's. All the 360Q had some variant of HX60n (n is any number in that series).

Anyone wanna stick a thermal probe in a 360Q and post the results?

If only I had or knew where to get one of those...I shall do a quick Google search.

[derekleffew]

I was going to do it, but my infrared thermometer only goes to 250°C, so that's pointless.

I wonder if Kelite would have this information handy? One would think Apollo has done lots of testing of gobos in various instruments.

[CrazyTechie]

I was going to do it, but my infrared thermometer only goes to 250°C, so that's pointless.

Sad day. I have some potential good news. My dad has a multimeter that also has a temperature probe that will go up to 1,832˚F. Its this one in particular Amazon.com: Digital Multimeter 7 Function (623-GDT-200A) Category: Clamp Meters and Multimeters: Home Improvement

So next question, how long should I leave the light on before I touch the probe to the shutter?

[gafftapegreenia]

I've gotta tell ya, the lamp/reflector housing of a Source 4 still gets pretty freakin' expletive hot. Thank ETC they put the plastic handles on the 750 caps.

[CrazyTechie]

I've gotta tell ya, the lamp/reflector housing a a Source 4 still gets pretty freakin' expletive hot. Thank ETC they put the plastic handles on the 750 caps.

For sure I will second that as I found out today. And I've still got my fingerprints which is always good!

[derekleffew]

...So next question, how long should I leave the light on before I touch the probe to the shutter?

With the lamp at 100%, do a test at 5, 10, and 15 minutes. I doubt there will be much if any difference. Let us know. Also make sure to tell us the lamp type and wattage, and the voltage applied. Use applicable PPE, and be sure to read, understand, and follow all safety instructions that came with your meter.

I've gotta tell ya, the lamp/reflector housing of a Source 4 still gets pretty freakin' expletive hot. ...

Not as hot as the heat sink on a freakin' expletive Selecon Pacific!

[CrazyTechie]

Okay thanks, so my game plan will be to test a 360Q 6x9 with 575W and 750W, assuming I can find one of each, and to do the same test on a 575W S4 and 750W S4 for comparison using the same probe. I was already planning on doing tests at five minute intervals. I'll try to get it done sometime tomorrow but I don't know If I can get all of the tests done as I still have work to do.

I'll be sure to keep everyone updated though.

[derekleffew]

We'll give you five days to complete your experiments. Wait until the poll closes to post your results.

[CrazyTechie]

Sounds like a good plan to me.

[jglodeklights]

Woo. Yay experiments!

[LXPlot]

If you could, try cooking an egg on the two fixtures. Because if I could eat in the theatre I could spend a lot more time there.

[xander]

If you could, try cooking an egg on the two fixtures. Because if I could eat in the theatre I could spend a lot more time there.

It's been done.

[jhdesynz]

It's been done.

Yup. We used to use a 360Q 6x9 to keep our lunch hot while working tech when the theatre was dark.

There is also a certain vendor who will go unnamed who his famous for his Source Four PAR-b-Que at LDI.

[CrazyTechie]

If you could, try cooking an egg on the two fixtures. Because if I could eat in the theatre I could spend a lot more time there.

You've no idea how badly I want to go into work with pancake batter and a frying pan and just rig up a 360Q and cook pancakes right now.

[chausman]

We show people how hot they get by burning pieces of paper!

[CrazyTechie]

So the time has finally come to post the results of the tests I’ve done. In order to verify that my probe was accurate and working I decided to boil some water on the stove and check the reading on the probe against another thermometer I had lying around. Both of them came in around 200-202°F which told me that my probe was fairly accurate when I did the tests.

When I conducted the tests I placed each of the lights, one at a time, onto one of our trees and then turned it sideways so that the accessory slot was now on the side instead of on the top. I did this to keep excess heat from ruining my equipment. I then built a jig that would hold my probe for me that I would just have to position right before I turned the instrument on. When I positioned the probe I tried to get it as close to touching the backside of one of the shutters that I had shuttered in half way.

Alright the results:

S4 575W Power:120.7v Lamp: HPL/120v/575W
05 min: 261°F
10 min: 290°F
15 min: 308°F

S4 750W Power:121.2v Lamp: HPL/120v/750W
05 min: 330°F
10 min: 361°F
15 min: 386°F

360Q 575W Power:120.5v Lamp: HX600
05 min: 579°F
10 min: 682°F
15 min: 745°F

Now you’re all probably wondering where the 750W measurements are for the 360Q. I was unfortunately unable to obtain a 750W lamp for the days that I would have been able to do the testing. So here is what I did: I decided to divide the S4 575W measurement by the S4 750W measurement in order to get a ratio for the difference between the two. The average ratio I got for all three measurements is 0.797 rounding to the first three decimal places. (i.e. [308/386] = 0.797)

Once I had this ratio I was able to project what the results would be for a 360Q with a 750W lamp. The results are as follows:

360Q 750W
05 min: 726°F
10 min: 856°F
15 min: 935°F

Now I’m sure some of you have been wondering why my results were so much lower than what ETC has stated to be what the gate temperature of a S4 is. Don’t worry I wondered this as well. Without knowing the specific details of how they conducted their tests, I can’t replicate them exactly. When I asked my TD about it he said it could be due to the way our instruments were manufactured. My solution was to take the numbers I’ve got and readjust them for if I had gotten the same measurements as ETC at my highest temperature.

To do this I took my measurement and divided it by ETC’s measurement and got another ratio. For the 575W lamp I got 0.495 (308/622) and for the 750W lamp I got 0.491 (386/786). Once I had this ratio I applied it to the numbers I have for the 360Q and got the following:

360Q 575W 1505°F (745/0.495)
360Q 750W 1904°F (935/0.491)

It is important to note that these are adjusted numbers assuming ETC’s numbers are correct. (I’m not saying that they are incorrect, just that I have different data then they did).

So the official number I have for the gate temperature of the 360Q with a 750W lamp…well that’s the thing, seeing as how my numbers are projected for the 750W to begin with and I also readjusted the numbers for if I got the same results as ETC it’s hard to say. So take which one you like best and call that the gate temperature of the 360Q with a 750W lamp.

If anyone wants to confirm or deny any of my data and back it up with their own testing it may help us to zero in on what the gate temperatures of these instruments really are.

Photo Documentation:
Top row S4, bottom row 360Q

[derekleffew]

Fascinating, even if possibly flawed, results, CrazyTechie. I wonder if the tip of the probe should be touching the center of the leading edge of the shutter? Perhaps the best conclusion (and answer to your original question) is that the 360Q's gate is over twice the temperature of the S4's.

I found the following on the interwebs, from Help my Gobo is burning! « Goboman’s Blog :

The typical gate temperature of an older 1k unit, was over 1700 degrees at the gate, newer cool beam units, have dropped the gate temperature to less than 500 degrees.

However, since the "less than 500 degrees" is refuted by ETC's data, I'm not sure I trust the "over 1700 degrees" part either. But then again, with the FEL...

I guess our next step is for STEVETERRY to track down who at ETC did the tests resulting in the KnowledgeBase article, and for that person to further detail the methodology. Here is an article that conflicts the other report: KnowledgeBase: What is the Gate Temperature of a Source Four? - Electronic Theatre Controls

Flat field - 313 degrees C / 595 degrees F
Peak field - 485 degrees C / 905 degrees F

(So don't touch!)

The original cited above:
KnowledgeBase: Source Four Heat Ratings/ How Much Heat Does the Source 4 Emit? - Electronic Theatre Controls

I'm surprised you did not reach thermal velocity after fifteen minutes. Now I wonder how long that actually takes?

[MNicolai]

I think the answer may lie in the article you linked to, Derek:

Gate temperature of a Source Four ERS:
In a test condition created by placing one shutter blade into gate covering 1/2 of field, and placing the thermal probe on the backside (shaded) of the shutter, the maximum S4 gate temps (A-size) were recorded as follows: HPL 750w/115v/300hr=786°F

The purpose of the test appears to be not to measure what the free-air gate temp is, but instead what the surface temp would be of a shutter blade or steel gobo placed into the gate.

Between the two articles there is some amount of discrepancy, but that's likely attributed to how the bench focus is set.

[church]

looking at the three data points for each fixture they have not yet reached maximum temperature. Repeat with measurements at 20, 25 and 30 minutes to see if the temperatures have preached a plateau.

[Kelite]

I was going to do it, but my infrared thermometer only goes to 250°C, so that's pointless.

I wonder if Kelite would have this information handy? One would think Apollo has done lots of testing of gobos in various instruments.

Good day Derek and friends, sorry to be absent from a very relevant thread. Just returned home from the ProLight+Sound tradeshow in Frankfurt Germany and am catching up today.

IIRC we measured over 1,000 degrees F with a 750W lamp back in the days prior to 575W availability for this unit. Crystal will withstand these high temps, but most gobo buyers cannot withstand the price associated with actual crystal, as it is an organic substance grown in the lab, sliced and ground to optical quality. Joel (Apollo's owner) offered crystal to several large companies when asked for a product able to handle the high temps associated with the aluminum reflector and 750W lamp combination.
Borosilicate (think Pyrex) is much less expensive than crystal for manufacturing gobos, but has a tendency to 'slump' while under intense heat. I remember inspecting a b/w glass gobo in the late 1990's returned from CBS news agency that had heated to such an extent that it began to sag in the gobo holder. Unreal.

Great thread gang! There are many wise replies and CrazyTechie has gone the extra mile with his testing of these fixtures-

Bravo!

[xander]

S4 575W Power:120.7v Lamp: HPL/120v/575W
05 min: 261°F
10 min: 290°F
15 min: 308°F

S4 750W Power:121.2v Lamp: HPL/120v/750W
05 min: 330°F
10 min: 361°F
15 min: 386°F

360Q 575W Power:120.5v Lamp: HX600
05 min: 579°F
10 min: 682°F
15 min: 745°F

Are you sure your measurements were not in Celsius? That would put them in the same ballpark.

[icewolf08]

Ok, so I dug up the thermal probe that came with my DMM and decided to set up my own test bench on this. Seems that the more results the merrier, and I had the time to run the experiment, though I have one more unit to test (I am waiting for my units to cool down).

This is what I have tested so far: ETC Source Four 26˚ with Ushio HPL575/115 and a Strand Axial Leko 6x9 with Thorn HX-755. Measurements taken with an Extech EX830 thermal probe.

Here is a photo of the basic rig:
|
The blacktack to hold the probe in place was not the best solution, but it was the only high heat solution I have right now. Needs improvement.

Here are the results so far, I will list for both fixtures at the same time with the source four photos on the left and the Strand on the right.

Ambient Temp at start of testing (with probe on shutter):
Source 4 - 69˚F
Strand Axial - 72˚F
|

Less than 30 seconds after lamp on (forgot to hold the timer in the frame for the source 4):
Source 4 - 540˚F
Strand - 337˚F
|

Five minutes of burn time:
Source 4 - 593˚F
Strand - 883˚F
|

After 10 minutes of burn time:
Source 4 - 605˚F
Strand - 885˚F
|

After 15 minutes of burn time:
Source 4 - 611˚F
Strand - 885˚F
|

I will get to testing an HPL 750 and list the results later and compile a table. So far these results seem to be in line with ETC's results.

[icewolf08]

Ok, so I now have complete results with the HPL750 test. Here is a PDF with the data:

I have time and temp photos if people want, but they seemed superfluous to add a new set.

I don't lamp my strand units lower than 750W, but I have a couple SPH 575 lamps that I was sent for demo. If someone wants me to do that test I will.

[CrazyTechie]

Are you sure your measurements were not in Celsius? That would put them in the same ballpark.

Yes I just checked and it was reading in Fahrenheit, however it is an older multimeter which could explain why I have different results.

[icewolf08]

Yes I just checked and it was reading in Fahrenheit, however it is an older multimeter which could explain why I have different results.

In looking at your photos, it is probably not a function of age, but technique. The probe that I used is like a tiny bead which I put directly on the shutter. From your photos it looks like the probe you have is more like a meat thermometer, so it was probably measuring more of the ambient air temp inside the fixture. This probably gave you a lower reading as the air doesn't heat quite as much as the metal. Something else I noted from your photos is that in the source four tests, you had to leave the accessory slot open for the probe, this allows some venting. I did my testing with the lens tubes in place, I can't tell from your photos if you did the same.

[CrazyTechie]

In looking at your photos, it is probably not a function of age, but technique. The probe that I used is like a tiny bead which I put directly on the shutter. From your photos it looks like the probe you have is more like a meat thermometer, so it was probably measuring more of the ambient air temp inside the fixture. This probably gave you a lower reading as the air doesn't heat quite as much as the metal. Something else I noted from your photos is that in the source four tests, you had to leave the accessory slot open for the probe, this allows some venting. I did my testing with the lens tubes in place, I can't tell from your photos if you did the same.

Ah yes that makes perfect sense as to why I have different numbers. Yes I did have the lens tubes in for both instruments.