Beam angles, projector placement, modulation control, etc.

[Stuka]

I'm still asking questions without ever even seeing my first set of galvos, so please excuse any questions that might seem "elementary".

Given your normal, everyday home-built projector design, a couple of 200-500mw lasers, DT-40 pro galvos, and appropriate DAC board -

* Does the beam output from the galvos drop any lower than the base of the galvos (which would require an elevated projector mounting of some sort), or does all beam projection occur higher than the galvos?

*For those of you who have used beam effects from your projector, shot SAFELY over your viewing audience -

If you're using your projector primarily for graphics on a screen, would it be best to redirect the beams using a bounce mirror on the screen, or using a bounce mirror inside the projector with a separate output window?

* Modulation - I would like to be able to "manually" vary the laser modulation for testing, experimenting, etc. without requiring computer control through the DAC board. Could anyone recommend a variable 5-volt circuit that would be suitable?

Thanks!

Randy

[wes]

* Does the beam output from the galvos drop any lower than the base of the galvos (which would require an elevated projector mounting of some sort), or does all beam projection occur higher than the galvos?

*For those of you who have used beam effects from your projector, shot SAFELY over your viewing audience -

If you're using your projector primarily for graphics on a screen, would it be best to redirect the beams using a bounce mirror on the screen, or using a bounce mirror inside the projector with a separate output window.

Thanks!

Randy

i don't know much, but i know pangolin w/live pro can take care of both of these issues.

it lets you set zones for beams and you take care of limiting height above audience during set up.
the beams will not occur outside the zone you designate.
same thing for graphics.you designate a graphics zone to fit your screen.
we just hang sheer material from the ceiling and project onto that.
of course you can reverse text and such so it comes out forward reading.
pangolin is expensive though,so i wonder if anyone knows if the lafreak package has these capabilities.

i'm just guessing,but i think using a bounce mirror would likely distort graphic images(i may be wrong on this though.) and if you are talking about projecting graphics out of the back of the projector while it is on stage,that may place you too close to your screen.(in the typical dj style setup i encounter.)

[Stuka]

Wes -

Thanks for the info!

Randy

[wes]

your welcome.
i hope you find all the info you need re:modulation etc...
i've got some experience but certainly not as much as many here.
if i were pressed to say the best way to project graphics to a screen onstage,i would say either back project through the screen or hang the laser up high in front of the stage.
for back projection i guess you want the power high enough for a good image but not too high so it bleeds forward heavily into the audience/performance space.
for both of these suggestions of course,you want to be sure you have clearance above the audience and stage people.
i know little about galvos so hopefully you can find out if there are other saftey procedures regarding downward pointing beams.
peace,
wes

[buffo]

* Does the beam output from the galvos drop any lower than the base of the galvos (which would require an elevated projector mounting of some sort), or does all beam projection occur higher than the galvos?

This really depends on how you design your projector, but in general the output beam can be directed both above and below the plane that the galvos are mounted to.

If you would rather only have beams directed from the mounting plane upwards, you can adjust the center point in your software upwards and then install a mask on your output aperature that would prevent a beam from dipping below a given plane, depending on how high the mask was.

Note that mounting the projector in an elevated position is quite common.

If you're using your projector primarily for graphics on a screen, would it be best to redirect the beams using a bounce mirror on the screen, or using a bounce mirror inside the projector with a separate output window?

I've never seen a projector used for both graphics and beamshows in the same show. (Well, that's not entirely true - I did see one projector that did both, but it had two separate pairs of galvos and a gm-20 actuator that either allowed the beam to pass to the beamshow galvos or redirected it to the graphics show galcos. But normally you either use two separate projectors, or only do one type of show or the other. As for me, when I do shows in my home, I simply move the audience!

If you want to use the same projector for both (and you don't want to install a second set of galvos), you'd need to mount the bounce mirror fairly close to the projector. Even then, you'd need some way to flip it up into the path of the scanned beams. (If you put a bounce mirror far away on the screen you can only send 1 beam back to the audience.) To send beam effects over the audience (sine waves, liquid sky, or fans of beams) you need to capture the full scan angle of the galvos and re-direct it back over the audience... I'm sure you could cobble something together to do this, but it sounds messy and very hard to align. (Not to mention a possible safety issue.)

* Modulation - I would like to be able to "manually" vary the laser modulation for testing, experimenting, etc. without requiring computer control through the DAC board. Could anyone recommend a variable 5-volt circuit that would be suitable?

There's a schematic in this thread.

Adam