# This is a short thread of messages about ETC Source Four conventional # units, originally sent to the "stagecraft" list, diving into engineering # and manufacturing changes made over time. ### Msg 1: Date: Fri, 1 May 2020 09:09:20 -0700 Subject: [SML] How to gauge the age of a Source Four? From: Jon Howdy all... are there any cast markings/numbers or other notations to determine an age of an ETC Source Four ellipsoidal body? Lens tubes have "Rev.[letter]" - does anyone know the years different Revs were? Anything like that on the bodies/barrels? How about the S4Par? ### Msg 2: Date: Fri, 1 May 2020 16:47:38 -0400 Subject: Re: [SML] How to gauge the age of a Source Four? From: Dale The source 4 middle bodies are, afaik, unchanged from the early days. Single and double yoke bolt versions were the only distinctions, I can recall. Reflector housings went through a couple of changes early on. Main one was adding baffles to the air vents facing back to reduce light leaks. The lens tube revs only matter when you have a broken one needing to be replaced or your are changing the glass out of an existing lens tube. ETC doesn't keep old revisions in stock, so you have to purchase a matching pair of the newest revision, and the unbroken half of the old lens tube goes into the bin of misfit parts, in hopes that it will be useful for a future broken other half of the same revision lens tube. Trying to mate different revs of the left and right lens tube castings is an exercise in futility. they designed the mating lips of the two castings so they only fit together properly with the same rev. You can force them to go together, but now the lens tube is out of round, leading to glass falling out when it's bumped, and it won't fit into the rest of the fixture easily. The lamp caps are the old 575 watt or below only, 575/750s, and the dimmer doubler ones. There are lots of the old 575 caps around that people drilled out to allow 750 lamps to fit, but they need that extra heat sink and light blocking casting to handle the heat long term. When you don't have that extra heat sink, the heat messes up the dichroic coating on the reflector, giving it a case of dandruff. (flakes falling off) At that point you have to replace the reflector, which is a bit spendy. Dale ### Msg 3: Date: Sat, 2 May 2020 11:03:34 -0700 From: Jon I was able to go into my facilities yesterday to start prepping for a buncha new fixtures, and found some interesting things, and I'm curious about any other "changes" that have come to the Source Four over the years... I have some bodies that are 2015, and others that are 2006. All use 575w HPLs, some long-life, none at 750w. All the 2015s all have cooked-off paint on the lamp housing. The 2006s still look fine. The reflectors are clean on both bodies, but the 2015 reflector has a definite 'cooler' color to it... the older ones have a warmer tone. But they're clean - no haze. So have there been changes in paint? Reflector coatings? - Jon ### Msg 4: Date: Sat, 2 May 2020 20:27:54 -0400 From: Dale Paint flaking off of the lamp cap over time is normal, and the photons don't care about that paint or lack thereof. I'll speculate here, but I think ETC switched to a low or no VOC paint process and the different coatings react differently. Paint adhesion over time is one of those simple sounding things that turn out to be stupendously complicated. formulation of the paint, surface preparation of the painted surface, primer, application conditions, curing conditions, working life conditions. I took a dive into that a few years ago, and quickly bounced. Physics and chemistry and manufacturing and end users all matter. The reflectors, they do take on a yellowish hue on the reflector surface over time. This presumably changes how it reflects or passes the various wavelengths. I believe this is aging of the coating, but that really is just a guess on my part. It does change the light coming out the front, but I never had the means to actually measure it other than using the Mark I eyeball. It seems a bit darker, but won't try to quantify it more than that. I will say that some fixtures that were in night clubs, before they banned smoking, that the yellowish tinting of the coating was stronger, but a vigorous cleaning removed a lot of it. I have no doubt that ETC's local dealership would be more than happy to sell you as many replacement reflectors as you care to buy. Might just be easier to group the older fixtures for specials and the new ones for washes. Dale ### Msg 5: Date: Sun, 03 May 2020 07:33:35 -0500 From: *Hobbit* A vaguely related question, which I don't think I asked before ... I've found that some of the older 36-degree s4 units in particular were really hard to get focused right, like the optics were just screwed up somehow and beam edges always looked ugly no matter what I did ... and that included lamp optimization on the fly, which I got in the habit of doing routinely because I could usually get a lot more brightness out of every unit. But the older 36es, usually units *without* the 750 model caps, were just constantly balky and ugly and dim by comparison. I think I remember seeing yellowed reflectors in some of them, but that wasn't the only problem. The lens train just didn't seem designed right. Later units improved somewhat, and I think the lens elements got moved around in the later barrels but I'm not dead sure about that. If anyone's got lens-tube placement graphics from different eras, that would be an interesting thing to compare. _H* ### Msg 6: Date: Sun, 3 May 2020 08:37:37 -0700 From: Jon For what it's worth, I've never liked the look from a Source Four 36 degree, for exactly what you've described. I also have no EDLT lenses, so I don't know if that would make a difference. But like you said, the edges were terrible, and trying to match fixtures was impossible. ### Msg 7: Date: Sun, 3 May 2020 13:57:43 -0400 From: Sean ~15 years ago Michael Eddy posted this to the list re: 36B0 lens tubes From: "Michael S. Eddy" Sent: Oct 6, 2005 3:49 PM To: Stagecraft Subject: Re: Source 4 lens question Having worked at ETC when the S4 was introduced, I can answer these questions. The lenses for the S4 ERS vary by focal length. The 19, 26, and 50 degree instruments use a single aspheric lens. The front portion is cast and the rear lens is partial cast and ground similar to a camera lens. This allows for the proper focal length in one lens rather than two lenses like a typical ERS. (You lose 4% of light with every air to glass transition, so by taking out one lens, you get back 8% back. This added to the other efficiencies to get more light with a lower wattage lamp.) The direction of the lens placement is important. Getting them reversed is not a major issue, but two fixtures of the same focal length, with mixed up lenses, next to each other will not line up or focus correctly. The problem with a single lens for the 36 degree unit was that the zero-crossing of the beam was right at the color, causing the appropriately named "Bonanza Effect" and the gel would torch itself! To solve this problem the designers came up with a combination of a high-contrast meniscus* front lens and a bi-convex rear lens for the 36 degree units. And in case you care, the 5 and 10 degree fixtures use an acrylic Fresnel lens. This saves on weight. *For the total geek, here is the explanation of a meniscus lens: A lens having two spherically curved faces, one convex and the other concave, so that it has the form of a shell. A positive meniscus lens is thicker in the middle than at the edges and serves as a converging lens; a negative meniscus lens thickens toward the edges and works as a diverging lens. Very large telescopes may use meniscus mirrors, which are lightweight and require an active control system to retain their shape against gravity. Michael S. Eddy Eddy Marketing & Consulting ###