Lamp Train Traveling as Iris Opens and Closes

[Footer]

I spent today maintencing two spotlights in Mrs.Footer's mainstage venue. The spotlights are 1970's vintage. I opened up the fixture and saw one of the weirdest things I have ever encountered in a fixture. As you close the iris, the lamp train runs towards the front of the fixture. As you open the iris, the lamp travels towards the back of the unit. The iris does not travel nor do any of the lenses of the unit.

The hotspot of the unit does change as you run the iris. When the iris is completely open, there is a very noticeable dark spot in the center of the beam. When the iris is closed, there is a very strong hot spot.

So, the question to CB land...

Why does this unit do this? What optically is happening with the hot spot?

 

[SteveB]

Obviously designed to intensify the light output as the iris/beam gets smaller. Is there possibly no adjustment to zoom in using lenses ?, which is the "normal" method for using spots at varying throws and is how it's done on the follow spots I use/have used, Strongs and Lycian carbon and xenons. Without a lens zoom function the lamp moves to compensate.

Never seen this. Sounds like an wonky Altman invention.

 

[Footer]

Obviously designed to intensify the light output as the iris/beam gets smaller. Is there possibly no adjustment to zoom in using lenses ?, which is the "normal" method for using spots at varying throws and is how it's done on the follow spots I use/have used, Strongs and Lycian carbon and xenons. Without a lens zoom function the lamp moves to compensate.

Never seen this. Sounds like an wonky Altman invention.

Nope, no "trombone" on this unit.

 

[LightStud]

Had you ever operated one of these fixtures before maintaining it, you'd know what was happening.

Why does this unit do this? What optically is happening with the hot spot?

This was widely touted as a "feature" of many early Lycian followspots (1980s, not 70s). In particular, the SuperArc350 and SuperArc400 series. The advertising for these fixtures stated "Intensity increases as spot diameter decreases." The specs for Lycian #1266 state "Units that iris down without increase of light output shall not be acceptable." It was an innovative feature, but one perhaps too radical or too far ahead of its time. Most lighting designers didn't like the idea of intensity changing based on spot diameter.

One instance where this feature is truly desirable is on an ice show, since the throw distances can vary greatly. Running a Trouper or Super Trouper, the operator will run the trombone rather than the iris for spot size control. (In fact, according to the Instruction Manual, "Spot Size Control Handle" is the trombone's proper name, look it up!) The bone is pulled back when the skaters are near, and pushed forward when the skaters are far away, thus maintaining a constant intensity over the travel (at least in theory). Following a skater from one end of the ice to the other and back can wear out an operator almost as much as skating himself.

Lycian was trying to improve upon the Strong units by combining two movements into one automatic operation. It failed because designers and operators preferred to have the two features separate.

 

[SteveB]

Thanks LightStud

I wasn't sure if it might be an early Lycian. Only once ran a truss version and as I was hanging 25ft on a truss chair, didn't take the unit apart to examine how that worked.

 

[WooferHound]

We have 2 Lycians at the Von Braun Center where I work. The iris is controlled by a huge lever on the back of the light and it also controls the lamp position to keep the hot spot within the iris area. There is a small wing nut on the iris lever that can be loosened to prevent the lamp from traveling which disables that feature.

 

[derekleffew]

Footer, are they the Lycian SuperArc350? With the iris controlled by a submarine wheel on the side? While I was never very fond of them, please post pictures, as I can't seem to find a single one on the 'net.

EDIT: Or, I suppose I could just put that pile of dusty magazines to use and scan in an ad.


Lycian SuperArc 350. Theatre Design & Technology, Summer 1984 issue.

If I'm not mistaken, this was the only model Lycian offered when they first started out, around 1981. A short-throw model came next. When the GE Marc350 lamp was replaced by the HTI400, new models were released and this line scrapped.

 

[derekleffew]

Wow, and only $340 for the 50-hour (Consider yourself really lucky if you get 35 hours before the output goes yellow, brown, or dim) EZT, GE MARC 350/16T, lamp!

https://www.interlight.biz/light-bulb/EZT

While it's often difficult to believe marketing ads and hype, in this case, a competitor's ad is even more true now than it was then.

From the same periodical as cited above.