Mounting lasers on stage

[Jem]

Your actual answer was pretty much "it just was, ok?".

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

You are obviously quite a sensitive person who has simply misinterpreted what I was saying and misconstrued it as me being offhand. Nothing could be further from the truth, i'm quite a nice guy, honest

As for name dropping... Never even crossed my mind. I guess you must be easily impressed

[smokeAndMirrors]

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

You are obviously quite a sensitive person who has simply misinterpreted what I was saying and misconstrued it as me being offhand. Nothing could be further from the truth, i'm quite a nice guy, honest

As for name dropping... Never even crossed my mind. I guess you must be easily impressed

Och, sometimes I don't so much get the wrong end of the stick as the wrong stick Sorry if I was snippy.

And yes, I am easily impressed by people who know what they're talking about.

[Jem]

And yes, I am easily impressed by people who know what they're talking about.

Oh Damn, that counts me out then, I guess i'd better shut up

[buffo]

a fan has higher energy density than any other scan pattern (all other things being equal).

Not quite. A fan has higher energy density AT THE VERY ENDS OF THE FAN when compared to all other scanned patterns, since at the ends of the fan the mirror has to make a 180 degree turn, which is (obviously) the largest turn it can make, thus you have the highest "dwell" time on a single point while the mirror reverses it's velocity. But the center of the fan has the same energy density as any other scanned image. (You'll also notice that the performer is not standing at the edge of the fan in that picture.)

But really, all this is irrelevant when you're talking about *skin* exposure (which has a much higher threshold for damage). Even at the ends of the fan, the power density is nowhere near as high as you would have with a static beam. So long as the beam is scanning at a reasonably fast rate (30Kpps, let's assume), the fan is many orders of magnitude safer than the static beam - even at the ends of the fan.

Adam

[allthatwhichis]

Ahhh... I feel that the lack of emotion in the written word is coming into play here. This is one of the problems with forums, it's not always easy to express feelings and emotions in simple text.

That's what the smileys are for...

[danielbriggs]

Hi Dan, the first of those two looks incredibly flimsy. You need something much more substantial.

I have two truss clamp positions on my RGB that I use where possible, but also use a tripod when it's the best option (bearing in mind what Steve said about vibration and movement; I would only use the tripod on a solid concrete stage).

I think Carl B uses the mounting method that you described but I have installed the top hat mount in to the chassis of the projector, and from memory your toblerone has an extremely solid frame so maybe that's an option?

Cheers Ian,
I know you're fairly knowledgeable in that sort of area, so could you suggest a decent tripod if the ones I suggested are naff...?

You're right, I could mount a top hat to the base of it.
If I did, I'd probably make it removable, or use some sort of quick release with it, as I know I wouldn't want it on all the time.
I'd also have to find the centre of gravity of the thing first though

Ta,
Dan

[smokeAndMirrors]

Not quite. A fan has higher energy density AT THE VERY ENDS OF THE FAN when compared to all other scanned patterns, since at the ends of the fan the mirror has to make a 180 degree turn, which is (obviously) the largest turn it can make, thus you have the highest "dwell" time on a single point while the mirror reverses it's velocity. But the center of the fan has the same energy density as any other scanned image. (You'll also notice that the performer is not standing at the edge of the fan in that picture.)

But really, all this is irrelevant. Even at the ends of the fan, the power density is nowhere near as high as you would have with a static beam. So long as the beam is scanning at a reasonably fast rate (30Kpps, let's assume), the fan is many orders of magnitude safer than the static beam - even at the ends of the fan.

Adam

Gotcha. Though my point was that the average energy density over a fan of length L would be notionally E/L whereas for a tunnel of diameter L would be E/(pi*L) where E is proportional to the energy in a static beam. And whilst these are crude calculations, LaserSafe shows a safer rating for a tunnel or triangle than a fan, all other parameters equal.

[smokeAndMirrors]

Meanwhile, back on the OP, I have seen this:

http://www.htfr.com/more-info/MR264746

which would fit nicely onto a tripod and hold the laser from the top.

[buffo]

It depends on what you mean by "all things equal"... If you're saying that the width of the two patterns is the variable that is held equal, then yes, the tunnel is safer, but that's only because the linear distance around a tunnel is a lot longer than the diameter of the tunnel. The laser is tracing over a longer "line", thus the average power along that line is lower.

However, if you instead compare the circumference of the tunnel with the width of the fan, your calculation yields the same energy density. (Which, as we've already discussed, ignores the fact that there will be slight "hot spots" at the ends of the fan, which you obviously won't have with a continuously-scanned tunnel.)

The difficulty in calculating the MPE for a scanned effect like this is the main reason why ILDA is suggesting a simpler approach, detailed here. It requires only a single measurement of a static beam at the closest point of audience approach.

Adam

[smokeAndMirrors]

The difficulty in calculating the MPE for a scanned effect like this is the main reason why ILDA is suggesting a simpler approach, detailed here. It requires only a single measurement of a static beam at the closest point of audience approach.

Cheers buffo, that's an interesting read. Can't find the details about the Laser MPE meters easily, though. Hitchin is just down the road, too. I bet they cost scary amounts.