Mounting lasers on stage

[smokeAndMirrors]

I'm starting work on a new show with a band, and I want to have my lasers relatively low down (possibly near floor level). My tripod stand are minimum 1m high and because of the spatial constraints of small venues it may be hard to get the larger tripods in. Plus there's no way to mount a single laser on a tripod without it toppling (they're ~600mW RGBs, about 6kg). So I'm looking for a way to mount a laser quite close to the floor. A flight case won't work because I need to tilt the laser up at an angle (I considered putting a laser on top of an amp at one point but I'm guessing this is not so clever?).

So has anyone got some suggestions as to how to mount my fixtures?

[Jem]

Hi

It would be useful if you could give us some idea as to where in the world you are. The reason for this is because there are different laws depending on which country you are in.

For instance, if you are in the UK or the USA there is no way you would be able to use a floor mounted laser for a public show.

It may be useful to have a read at this article...

http://www.hse.gov.uk/pubns/priced/hsg195.pdf

Cheers

Jem

[smokeAndMirrors]

Hi

It would be useful if you could give us some idea as to where in the world you are. The reason for this is because there are different laws depending on which country you are in.

For instance, if you are in the UK or the USA there is no way you would be able to use a floor mounted laser for a public show.

It may be useful to have a read at this article...

http://www.hse.gov.uk/pubns/priced/hsg195.pdf

Cheers

Jem

Hi Jem,

Yeah I'm UK based. The document states

"In circumstances where access restriction is not possible, eg during deliberate audience scanning, safety assurance becomes more an issue of controlling beam hazard so that applicable exposure limits are not exceeded. The height of the scanning beams is particularly important, eg above audiences on a dance platform. A minimum height of 3 m above the highest dance platform is recommended."

As I said, I want to tilt the laser up and this will easily give 3m clearance. Also I've done my MPE calculations using software and I max out at a little less than 0.1*MPE, well within the exposure guidelines.

Unless I've missed something - which I probably have! - that should be sufficient?

[aclasers]

Depending on your projector you can secure it to box truss using doughty clamps,

As jem said, there is H&S issues first,

If the stage is high and projection zone can be in the saftey zone, and no perfomers etc etc.,

[norty303]

You can buy long G clamps, so you could use your tripod with a T bar (and counterweight on the other side if needed to balance) at minimum height and then extend the projector towards the floor on the long clamps.

I find they're useful when you have a truss flown quite high for lighting but you want your laser beams more perpendicular to the floor such as behind the DJ's head. saves on having extra stage clutter from tripods and risk of knocking from passing traffic upsetting carefully set up targets and the like.

[Doc]

Or use a tophat pole mount on your tripod.

http://www.djsupplies.co.uk/speaker-...35mm-463-p.asp

I would be very surprised if you could even see a beam that was 0.1 x MPE and unless your audience is *very* far away; that you would achieve that value with 600mW lasers.

[smokeAndMirrors]

Or use a tophat pole mount on your tripod.

http://www.djsupplies.co.uk/speaker-...35mm-463-p.asp

I can't see how the top hat helps unless I mount the laser upside down?

I would be very surprised if you could even see a beam that was 0.1 x MPE and unless your audience is *very* far away; that you would achieve that value with 600mW lasers.

LaserSafe PC tells me that for a scanning effect

Wavelength = 532nm (green, the most powerful diode in the box)
Exposure = 5s scan time (average)
Power = 0.6W
Beam diameter = 4mm
Divergence = 15mr (estimated)
Target dist = 5m (to audience)
Scan angle - 90 deg
Scan freq = 20kHz (I think it's actually 25)

the emission is 0.142*MPE

In practice, I'd not be getting peak power all the time, and the power of the blue and red are quite a bit lower, so unless I'm mistaken this is an upper bound and quite within the safe zone.

[mixedgas]

WARNING, you have one detail wrong on the maths.

Better divide that scan freq by 10. 20 kpps or 30 k pps is NOT 20 kilohertz, the best galvos can only do about 2500 hz sinusoid, and much less then that square wave. This is why we tell people to use a photodetector and a oscope to measure scan rates.

Steve

[buffo]

20 kpps is NOT 20 kilohertz

Exactly right!

To wit: 30Kpps = ~2500Hz small step bandwidth with *significant* distortion.

Smokeandmirrors:

Remember... The center circle of the ILDA test pattern is actually made up of 12 points which all lie *outside* of the center square. Yet on a properly tuned set of scanners, this appears as a smooth circle that lies *inside* the square. That's some serious position inaccuracy there, and even so the max frequency is only 2.5Khz. (12 points around = 1 cycle = 1 Hz for a small step signal, thus 30Kpps yields 2.5Khz.)

Or: Kpps speed divided by 12 = rough small signal bandwidth limit.

Adam

[smokeAndMirrors]

Ok, that's useful information. Figure is now 1.59*MPE for a line, .564*MPE for a circle. Care to be taken for sure.

But I'm still none the wiser as to how to mount the laser, which is the topic of the OP. And I seriously doubt that lasers can't be mounted on the floor; the Australian Pink Floyd for example:



(in the actual show I saw they were a bit lower).