Design Issues and Solutions Help with aiming lights from a fly up/down truss(no catwalk)

Goldartfrog

Member
Joined
Oct 22, 2019
Location
Urbana, Illinois
Hello everyone, thanks in advance for any help.

I'm in charge of lighting for my high school theater, and we're putting on a show that would ideally have 12 specials.

This shouldn't be a problem, as they are marked out on the stage, except that our theater has a large truss that most lights are hung from. The only way to access the lights on the truss is to lower it, move each light with no reference as to where it will end up, and then raise it back up and hope you got them right. There have also been problems with the truss cables getting caught in the winches (things that have been fixed), however I would like to minimize the amount of raising/lowering we do with the truss.

My question is: Does anyone have any formulas, tricks, tools, measuring devices, or just general advice on how to aim lights when you can't see where they are going to throw?
 

theatricalmatt

Well-Known Member
Joined
May 25, 2013
Location
New England
You've discovered the joys of bounce focusing lights.

A few notes from my own experience --
1) It gets much easier with practice, especially if you deal with a rep plot and similar focus points.
2) Having an accurate * 3-D * draft of the lighting plot and facility can help tremendously, though it's no substitute for experience.
3) Some people have invested in inclinometers (to measure and mark exactly how units were focused). You'll want to mark all of your fixtures with identical index lines, to provide a baseline for measurement.
4) Moving lights solve nearly all these problems for you (but introduce a few of their own).
 

DrewE

Well-Known Member
Joined
Mar 18, 2019
Location
Vermont
Being that this is a high school, maybe you could team up with a math class studying trig and have them determine the proper angles for the lights to hit the desired locations on the stage. In theory it's a pretty straightforward problem in trigonometry and three dimensional geometry, albeit not one I care to figure for pure fun in my copious free time.

(Is it truly impossible to safely access the truss with scaffolding or even ladders or other equipment? In my high school, some years ago, the house electric was accessed using a Genie hoist equipped with a "super straddle" gizmo that enabled it to be lifted up above the house seating. It was somewhat of a pain to set up and use, but it got the job done.)
 

derekleffew

Resident Curmudgeon
Senior Team
Premium Member
Joined
Aug 21, 2007
Location
Las Vegas, NV, USA
One needn't know nor understand maths (high-school geometry), other than "angle of elevation = angle of depression." One can use a real inclinometer, a level and protractor, or a smart phone's "level" app.


https://www.harborfreight.com/dial-gauge-angle-finder-34214.html

1. With the batten at trim, stand on stage in the desired location. Sight or point up at a fixture's lens and measure the angle, up from horizontal (angle of elevation).
2. Lower the batten to working height. Tilt the fixture down from horizontal (angle of depression) until it matches the same angle when you were on stage.
3. The pan will be the same regardless of the height.
4. Take the batten back to trim and check your work. Rinse and repeat as necessary.
 

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
One needn't know nor understand maths (high-school geometry), other than "angle of elevation = angle of depression." One can use a real inclinometer, a level and protractor, or a smart phone's "level" app.


https://www.harborfreight.com/dial-gauge-angle-finder-34214.html

1. With the batten at trim, stand on stage in the desired location. Sight or point up at a fixture's lens and measure the angle, up from horizontal (angle of elevation).
2. Lower the batten to working height. Tilt the fixture down from horizontal (angle of depression) until it matches the same angle when you were on stage.
3. The pan will be the same regardless of the height.
4. Take the batten back to trim and check your work. Rinse and repeat as necessary.
@Goldartfrog In addition to all of the above; there are also focusing trusses and bosun's chairs, although I doubt either of these would 'fly' past your school's administration and / or insurers. At least one theatre in my neighborhood has (or had) two FOH pipes approximately 40' wider than their prosc' flown on synchronized chain hoists with separately flown focusing tracks. I've toured a production from Toronto, to Calgary, to SanFranCisco and into Broadway's Shubert carrying our own FOH focusing track with us all the way.
As previously stated: I suspect this wouldn't 'fly' in any sense of the word in your situation.
Toodleoo!
Ron Hebbard
 

cbrandt

Well-Known Member
Joined
Dec 7, 2011
Location
Michigan
You might consider a focus tape on the floor. They're more often used for loading in large productions to new venues, or re-setting a rep plot, but I think you could play around with a bit and make it useful for your space. As all have said, bounce focusing is an art, and it takes a lot of time to get good at it.

A question no one has asked, how high is your up trim height? Could the school provide a single person or scissor lift of some sort, with a qualified operator?
 

Buttmonkey

Member
Joined
Oct 29, 2019
Location
IL
Hello everyone, thanks in advance for any help.

I'm in charge of lighting for my high school theater, and we're putting on a show that would ideally have 12 specials.

This shouldn't be a problem, as they are marked out on the stage, except that our theater has a large truss that most lights are hung from. The only way to access the lights on the truss is to lower it, move each light with no reference as to where it will end up, and then raise it back up and hope you got them right. There have also been problems with the truss cables getting caught in the winches (things that have been fixed), however I would like to minimize the amount of raising/lowering we do with the truss.

My question is: Does anyone have any formulas, tricks, tools, measuring devices, or just general advice on how to aim lights when you can't see where they are going to throw?
It's called a blind focus, the only way ik to completely get rid of your problem is to get a harness and a hand of god installed on your truss so you can raise up your truss while someone rides up and put the lights where you want them before you lower the truss to let them off.
 

JonCarter

Well-Known Member
Joined
Apr 18, 2011
Location
Meridian, Idaho, US
I've held my piece on this one, waiting for some newbie to arrive at what worked 60 yrs ago. We used to put the smallest kid on the crew on the light bridge with a Crescent wrench (didn't have things like "safety harnesses" back then; just told her/him to be careful & hang on), ran it up to trim and focussed away.

Yes, we let the kid down before we went home for the day.
 

FMEng

Well-Known Member
Fight Leukemia
Joined
Mar 31, 2008
Location
Tacoma, WA
Regarding inclinometers, the Android app called "Tool Box" has a good one. I have found it to be very accurate, at least on my Samsung S9. I recently used it to adjust the elevation of a 3.8 meter satellite antenna and had signal on the first try. Considering the path length is 22,500 miles, a few tenths of a degree is a big error.
 

jonliles

Well-Known Member
Fight Leukemia
Joined
Sep 8, 2008
Location
Marietta, Georgia, United States
You can make a DIY Inclinometer with a Speed Square and a short length of string with a weight (make-do plumb-bob) hung from the pivot point. Stand in the spot where you want the focuse/hotspot to be, site along the speed square up to the center of theluminarie's lens, pinch the string to capture the angle, mark it with a pencil. bring down the the trust, hold "inclinometer" along the long axis Center line, and adjust the angle of the instrumet. Rotation of the instrument you'll have to figure out on your own.

Great teaching moment for a teacher and students.
 

bmiller025

Member
Joined
Jul 12, 2006
Location
Colorado
Bounce focusing is the simplest and cheapest approach, but it might be worth looking into whether your school district or even your school has a Genie Lift that can be arranged for. I have designed shows in a school that has a very strange auditorium, with front lights mounted on a truss 32 feet off the floor. They have hired me to come in and use a rented full size “cherry picker” to change out all lamps in the incandescent fixtures (mostly PAR64s), and focus a few specials for the shows. This was only feasible once per year, due to the cost of renting the cherry picker.

If a lift and an operator is available, you will have to get good at describing exactly what you need regarding focus!
 

gafftaper

Senior Team
Senior Team
Fight Leukemia
Joined
Jan 2, 2006
Location
Seattle, WA
There have been a few really bad ideas suggested in this thread. The right way to do this is to bounce focus, use a scaffold, or a genie lift. That's it. People should NEVER ride a truss without a lot of very specialized equipment and training. The idea that a teen or the smallest kid on the crew is riding truss without any proper training or equipment is absolutely unacceptable today. Here on Controlbooth we firmly believe that this job is never worth risking your life over. The show must go on SAFELY or not at all. Do it right or don't do it at all. If a show looks bad because you didn't get the light focus right, too bad for the show, at least you didn't die before the show closed.

It's called a blind focus, the only way ik to completely get rid of your problem is to get a harness and a hand of god installed on your truss so you can raise up your truss while someone rides up and put the lights where you want them before you lower the truss to let them off.
No, this not acceptable unless you are using truss and rigging specifically rated for this use (most is not), a harness designed for this purpose (not just one you buy a Home Depot or one your uncle the rock climber gave you), a connection to the truss designed by a professional who has years of training (preferably they have certification by SPRAT and ETCP), and the person going up needs to have proper training... which probably also includes SPRAT certification.

We used to put the smallest kid on the crew on the light bridge with a Crescent wrench (didn't have things like "safety harnesses" back then; just told her/him to be careful & hang on), ran it up to trim and focussed away.
Yes, we all did dumb things back in the day and people died.
 

What Rigger?

I'm so fly....I Neverland.
Joined
Aug 24, 2006
Location
PPT.
It's called a blind focus, the only way ik to completely get rid of your problem is to get a harness and a hand of god installed on your truss so you can raise up your truss while someone rides up and put the lights where you want them before you lower the truss to let them off.
Well, hopefully after seeing all this, you've learned more than a single way to, and to not, do this. As for it being called a "blind focus", why not make a contribution and put it in the Wiki? Or realize there's a lot of different terms for a lot of different things, and that learning is a lifelong thing. There's tons of people here on the Booth smarter than your or me, with mileage to spare on the career path. It's unreal.