Source 4 36 degree lens tube focus problem

[lightwench]

I've been working on bench focusing my Source 4 inventory and have run into an interesting problem. While trying to sharpen the edge of a 36 degree light, I've noticed that I can see an inner circle no matter where I place the barrel. This circle has 4 spokes on it (like the ones holding onto the smaller lens). I've looked through this board and the ETC site but have yet to find anything that truly explains what's going on so I thought I'd ask here. Is this a problem with the lens or possibly the lamp? I've never noticed it before so I'm rather stumped. Feel free to ask any questions and I'm grateful to anyone who has any ideas.

 

[dramatech]

This is a very common problem on the 36* lenses. There have been many in depth threads on the lightnetwork forum on this subject. The best you can do is to adjust the bench focus knobs on the back. Start with lamp as far back as you can get it and then adjust for flat field watching for the secondary ring. It is a compromise between flat field and seeing the ring. The lenses of 1997 and earlier, exhibit the problem more than the newer lenses. You can identify the early lenses, by the fact that the lens element are held in place with four tabs and the rear 36* lens is inset from the back a bit more than the newer ones that have five tabs to secure the lens elements. Also the lamp holders on the earlier units dont have the securing clip and the lamp can move a bit forward and make the problem worse.
The problem drove me nuts for quite a while until I read up on the many posts. I also swapped lens elements around so that all of my 36* tubes are of the newer type, and eventually upgraded all my lamp caps to the newer style. Even with all that, I have a Lighting Designer that likes hot spots in the center, and then complains about the secondary ring. His solution is to add some R132 frost to the instrument. Luckily I only see him about once a year.

 

[lightwench]

Thanks dramatech. I really should be more active in the lighting community in general but I tend to lurk and then get sucked into real life. Good to know that isn't me going crazy and seeing things. And thank you for the lightnetwork forum. Yet another place for me to go to find answers to things. I just spent probably too long futzing with those lights. They do look better than they use to but they still aren't pretty.

 

[lightsmith]

Hi.
I have seen this a lot in Source Fours, but it is only really noticeable in the 36 degrees. The problem is most likely that you have something out of whack in the lamp cap. Take the cap off. Unscrew the peak/flat knob. Now squeeze together the main parts of the cap. You should see seven threads of the bolt that sticks out. if you see less than that, then one of the wires or sta-cons is out of place. More often than not, it is one of the grounding sta-cons. Take the cap apart. There is a little slot at the base of the bolt that the necks of both sta-cons nestle into. It is surprising how this very small bit can result in just the symptoms you describe. Hope this helps.

 

[church]

I recently noticed a strange behaviour on two of my 36 degree S4s. When i use the bottom shutter it does not produce a hard cut instead it appears to produce a cut that is similar to a reduction in intensity that you would get from a mechanical dimmer and you are left with a double image of the shutter edge. The other three shutters work fine. I could alter the focus to get the lower cut hard and sharp but this put the other three shutters out of focus.

I checked the lens positions in the lens tube, swapped burner assemblies from a 50 degree fixture that did not have this problem, replaced the complete barrel assembly with one from a fifty degree did the same with reflector housing and finally concluded it is probably in the lens tube. I also bench focused this thing more times than I care to think about. The strange thing is nothing fixed the porblem but each of the changes had a small improvement. I talked with ETC three times during this and we eventually concluded that this is a quirk of the 36 dgree fixture and happens on some units - manufacturing tolerance distribution.

Has anybody else seen this and found a fix.

Normally I find the S4 shutters produce hard sharp edge cuts on all four shutters.

To be honest this is the first time I have seen this problem on any fixture from any manufacturer. fixtures

 

[MNicolai]

Maybe the shutter is just slightly bent. It's a stretch of an idea because there isn't much room in the shutter planes for variation, but maybe it is just enough to create an optical difference in the beam.

You could try taking the body apart, removing the shutter in question, and replacing it with a shutter you know works. Then test the fixture. If it works, you might be able to solve the problem just by spending a few dollars on a new shutter.

 

[church]

I should have mentioned when I changed the barrel it included a different set of shutters and it made no difference. I even swopped the original shutters around to no effect. I wondered if it was the plastic tips on the lugs that hold the barrel assembly but they were all in good condition. So I loosened the bolt that allows you to rotate the barrel assembly for Gobo alignment and tried moving the barrel assembly up and down and side to side and it also made no difference.

 

[MNicolai]

So does the problem travel with the lens tube? If you take that lens tube and put it in another fixture, that fixture then experiences these problems?

 

[derekleffew]

Peculiar. Makes no sense really as the bottom shutter (top cut) plane is physically between the top shutter and side shutters. Here's an experiment: try putting the lens tube in upside down, and see if the problem moves to the top shutter.

But I suspect the soft-focus issue will remain on the bottom shutter. I'd guess a degraded reflector, due to the heat the top portion is the first to lose its dichroic coating. You haven't mentioned cleaning or inspecting the reflector, have you?

From page 12 of Source Four Assembly Guide (Pre-2004).pdf or page 10 of Source Four Assembly Guide.pdf.

 

[church]

To answer dereks question first, one of the steps I did was to swap in a different reflector and housing from a 50 degree fixture that does not show tyhe problem. The result was it reduced the problem but did not eliminate it. I also rotated the lens tube through 180 degrees and you are correct Derek it made no difference. I did inspect the original reflector and it does indeed have a greenish tint to the top - this was why I swapped in a reflector assembly from a new 50 degree fixture.

To answer mnicolai's question the first thing I did was to swap in another 36 degree lens tube from a fixture that did not exhibit the problem and the problem was visible but less notceable than with the original lens tube. I then stuck the original lens tube into a fifty degree fixture and I now had the same problem but again only just noticeable. It seems to be a combination of lens tube, reflector assembly, barrel shutter assembly that makes this quite noticeable.

The 36 degree fixture is a 750W fixture I am not sure of its manufacture date but it does have a cUL approval so it is not that old. It is the original reflector in it.


I also tried removing the lamp and replacing it with a new lamp with the same result a slight improvement.

 

[Lightingman48]

Did you swap the lamp holder? I have just encountered this problem and found it to be an issue with the lamp holder.

I originally attempted to simply bench focus some more of my venues S4 36 deg. instruments (manufactured 04/07). I have noticed this condition before and did not have the time to investigate. When the "shadow" persisted in one unit, I swapped lenses, and did the other things you did.

As a "last" resort, I did a visual inspection of the lamp centering in the reflector. It was off to the low side of the instrument and would not move any further up. In messing around with the lamp holder I found that the alignment bolt was not tight and therefore the lamp tended to tilt slightly. After tightening, the lamp still will not move up as much as it will down, but, the shadow is gone for the most part. Seems to be a problem that is more evident with the 36 deg lens.

 

[church]

Yes Lightingman48 the lamp holder is down to the low side, I also checked the the other burner assembly I swapped in and this too was at the low side. It does not seem to affect a 50 degree fixture but does affect the 36 degree. I have not managed to move the lamp to a osition to correct this so I think it is time to strip these two burner assemblies and find out why the lamp is so far off centre.

 

[Scenemaster60]

I have a Source 4 focus issue with a lens tube that we have in inventory at a local theatre where I regularly volunteer. I have posted pictures of the tube at two different focuses below and then I cracked the tube open and took a look...

1. At this focus you can see the sharp focus of a faint inner ring of light, the soft focus line is the bottom shutter which also corresponds to a larger and much brighter outer pool of light at a slightly soft focus.

2. Here is the same shutter cut in sharp focus. Now the "inner ring" of light is in softer focus and there is odd flaring at the bottom.

3. Here is the barrel opened up. I am not all that knowledgeable about the various revisions of the Source 4 lens tubes, but I think that this likely one of the original design 1992-ish tubes. I infer this from the fact that there is absolutely nothing stamped anywhere on the tube that says "Rev. A" or "Rev. G", etc.; there are only 5 lens slots instead of 6; and the fact that the front color frame/accessory slots are both thin. Visually the lens placement looks correct, at least from later 36-degree lens barrels that I have worked with. We have 15 36-degree barrels in the inventory here and they range in age from the mid-1990s all the way up to "Rev. G".

With all of that said, my question is this: were there different lenses used in the 36-degree tubes in earlier iterations of the Sounce 4? Neither of the lenses in this barrel have ANY dots on them. I'm not sure if there never were dots OR if they got washed off inadvertently by a clueless volunteer. Is it possible that one or BOTH of these lenses belong in a Rev. G lens tube and that there is a set of lenses that belong in this tube floating around in another tube? We have not had any serious focusing issues with the 14 other 36-degree tubes.

Can anyone shed some light on this or should I just call ETC and chat with someone there who knows the history of the lens tube revisions?

 

[Scenemaster60]

Thanks to whomever combined my thread with this useful information! (I think it was Derek.)
From this is sounds like the 36-degree in the old tubes was just finicky in this respect.
I pulled the lamp out during intermission earlier and found that it was super far forward in the reflector and also that the lamp filaments were showing considerable "sag" as shown below. After curtain call today I will revamp, bench flat-field with a 50-degree lens and then see how the "naughty" 36-degree tube behaves.

Sagging filament, which would explain the blurry mess at the bottom of the field.

 

[Scenemaster60]

Well, these suggestions largely fixed the issue. I suspect if I tinkered around for a while longer I could get an even more even and flatter field. The lamp is ALL the way in the socket AND the lamp is as far back in the reflector as the burner will allow.

As you can see this is considerably better, very much within the "acceptable" range. As per one of the suggestions above, I may try migrating the 19 degree lenses into these 1st generation barrels and the 36 degree lenses into the Rev. G barrels.

 

[bdkdesigns]

With all of that said, my question is this: were there different lenses used in the 36-degree tubes in earlier iterations of the Sounce 4? Neither of the lenses in this barrel have ANY dots on them. I'm not sure if there never were dots OR if they got washed off inadvertently by a clueless volunteer. Is it possible that one or BOTH of these lenses belong in a Rev. G lens tube and that there is a set of lenses that belong in this tube floating around in another tube? We have not had any serious focusing issues with the 14 other 36-degree tubes.

I have this exact same question. ETC's website has no mention of a smaller front 36 degree lens. However, I just ordered a replacement front 36 degree lens to replace a cracked lens. This does not actually fit inside of the tube and will only fit into the 26 degree slot which is much closer (this gap isn't as great in newer models). As you can see in the image, the slot for the 36 is clearly smaller than the 26 slot. Simply putting it into the 26 degree slot creates slightly wonky optics, but it is the only way that I can get this 36 degree lens to fit. I've looked further into it and I've got 12 of these lens tubes in stock that had the lens replaced at some point and it didn't fit. Does ETC no longer make this smaller front 36 degree lens? My supplier when I ordered the part and posed the question didn't know that the front lens was was ever smaller than it currently is. I've always thought that my wonky focus 36s were part of the well known issues, I never once thought or had the time to check that ETC must have changed the lens size and placement up.