Hi, I'm a new house tech in an old theatre. All the equipment here has been handed down from other theatres over the past decades so I assume I am working with old S4 fixtures/barrels. In my researching I've heard that the 36 degrees, especially old ones, are particularly troublesome but haven't been able to find any solutions for my problem.
Not all, but some, of our 36 degree barrels have this strange double-image issue. Here's a video of just running the barrel. Note the constant double circle, especially when the barrel is pulled out:
S4 36 running the barrel.mp4
And here is a video of attempting to use a shutter with this issue. Note how it's impossible to properly shutter with the barrel out, and how you can even see the shadows from the lens holders:
S4 36 running the barrel with shutters.mp4
Any advice is appreciated! They're... usable, but not anywhere near ideal.
It's not ideal but on my units like that if you mess with the field knob on the back of the fixture you may get it more usable. I believe I typically tighten it (turn it clockwise), which makes the center of the unit darker, but depending on how I'm using the fixture that is better than a double image.
Youre right that does help a bit, it is a tradeoff though. From the bit of information out there it seems like some 36° barrels are just Like That, have you found the same thing? I've found it's mostly been old barrels but today I found a Rev J barrel that's pretty bad.
Edit: I've been doing more diagnosing and have figured out that the issue is actually more to do with the lamp housing. Still no clue what exactly the problem is but swapping the lamp housing makes the issue a lot less noticeable.