Laser project (prop) - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: October 27, 2018, 08:12:06 am
content: I have no experience with lasers...My sister is in the movie set construction business and asked me if I could make an ac powered laser prop that would shine an array of 5 visible red lasers. They want two arrays of 5 beams, and they need to project 5' minimum.They were planning to use off the shelf laser pointers however holding the buttons and batteries are proving problematic.If I orders these:https://www.ebay.com/itm/10Pcs-5V-650nm-5mW-Red-Dot-Laser-Module-Laser-Diodes-Sights-Laser-Pointers/192103230336?hash=item2cba3eab80:g:qsMAAOSwJ7RYUPzb:rk:2:pf:0do I need a lens or should I expect these to work if I simply connect them with a 5Vdc wall wort?

author: abraxa
author_rank: Frequent Contributor
timestamp: October 27, 2018, 08:55:24 am
content: They'll create a dot on whatever surface the beam hits but don't expect the beams themselves to be visible.In order for the beams to be visible, you'll need either smoke/fog or powerful lasers that are EXTREMELY dangerous.5mW is as high as I would go - some would argue that anything more than even 1mW is too much if you can't make sure that no one looks into the beams with their eyes. In my opinion, anything more than 5mW is asking for ruined lives, trouble and lawsuits.Safety dictates a low power output, so you'll want to make sure that the beam is as visible as possible. The human eye perceives a wave length of 635nm as significantly brighter than 650nm, so I'd definitely use 635nm modules. Green at 532nm (540nm) is even more visible but red is less dangerous to use (no infrared emission of unknown power) and... well... they asked for redSome visuals if you care for them:[635 vs 650nm comparison][Green Lasers: What Can Certain mW Do?]

author: PointyOintment
author_rank: Frequent Contributor
timestamp: October 29, 2018, 07:28:50 am
content: Quote from: abraxa on October 27, 2018, 08:55:24 amBut does the camera? This is for a movie prop.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 29, 2018, 10:41:03 am
content: Quote from: PointyOintment on October 29, 2018, 07:28:50 amIf the camera-display system has a reasonable white-balance, then by definition colors in the reproduced image will have similar relative brightness to reality.

author: dmills
author_rank: Super Contributor
timestamp: October 29, 2018, 12:21:32 pm
content: Be careful with laser display stuff around video cameras, the sensors really do not like being hit with the small spot size that results from a reasonable correlated laser source hitting the lens.... Film cameras are actually significantly better in this respect (You don't usually ruin the camera), but exposure can be tricky.You will find that the lasers look significantly brighter if filmed from almost on axis as the dust in the atmosphere preferentially scatters the light at small angles, push comes to shove a 'hazer' (Something like a DF-50 diffusion machine) will make the beams FAR more visible (But talk to your lighting cameraman about that).You really want to be posting this over on Photonlexicon where the laser geeks hang out.Regards, Dan.

author: ajb
author_rank: Super Contributor
timestamp: October 29, 2018, 03:35:41 pm
content: For something that looks nice to the eye, you probably want something at least 50mW, assuming relatively ideal conditions (otherwise dark environment, a good amount of particulate in the air, favorable viewing angle). Since cameras tend to be less sensitive than the human eye, and presumably you'll want other things in the scene lit for visibility, something closer to 500mW or even 1W with the ability to control the power would give you a lot more flexibility. Of course a lot of this depends on the type of effect you're after. You can probably make 5mW work, but it's going to be tough and you'll need to really plan the scene around the effect.Now I hate to bethatguy, but . . .Note that 5mW is the legal limit for laser products in the US without an FDA variance. Technically the equipment must be manufactured and certified under a manufacturer's variance, and would need to be operated by someone varianced to do so. Many enthusiasts avoid these requirements by not doing anything commercial, but putting laser equipment into a presumably commercial film shoot would definitely count as 'introducing into commerce', so you lose that loophole. Your chances of getting caught are probably quite low as long as nothing goes wrong, but if you want to keep things on the up and up it's probably a better use of everyone's time and money to hire someone in to do the work. In addition to the legal risk, using uncertified laser equipment can aggravate insurance policies, and especially in an environment like a film/tv shoot you really want someone who knows how to manage and operate the laser equipment safely. I know plenty of people who have the equipment and qualifications to help you out, so if you shoot me a PM I'll be happy to help you find someone and provide my bona fides.Quote from: abraxa on October 27, 2018, 08:55:24 amLOL "5mW". Nobody actually makes 5mW (or 4.95mW, as many like to claim) green pointers. Those specs are totally made up to get them imported into the US because nobody can be bothered to catch any but the most egregious importers. It's hard to tell from video, but I bet that thing is closer to 30mW, and because it's a shitty DPSS laser it's going to have a bunch of IR on top of that. 1064nm doesn't trigger your blink reflex, but will destroy your retina all the same!

author: PointyOintment
author_rank: Frequent Contributor
timestamp: October 29, 2018, 06:25:41 pm
content: Quote from: Wolfram on October 29, 2018, 10:41:03 amWhite balance is irrelevant. I'm talking about spectral sensitivity (and maybe also dynamic range).If you want to achieve maximum perceived brightness by the human eye, physically viewing the actual laser beam in person (not a video of it, because that's mediated by the camera and display device), then 635 nm is best, because that's the peak of the human eye's spectral sensitivity in that range. But the red filter on the camera's CCD (irrelevant whether it's 3CCD or a patterned filter) might have a peak at 650 nm instead. So you need to know that and optimize for that, not for the human eye, which will be viewing something else entirely and which you have no control over (the "red" light, whatever wavelength(s) that happens to be, emitted by the TV or projector).The goal here is to maximize the values of the data in the "red" channel in the video file,notto maximize the perceived brightness by the film cast & crew. A more practical way to do that might be to just accept that it will be seen dimly by the camera, try to ensure no other red things (including gray/white) are in the scene, and boost the red channel in post. Or, if your video editor is good enough, selectively boost red in areas that are only red (not gray/white).(Dynamic range may also play a role. Most cameras have a much smaller dynamic range than human eyes, too. But they can easily shift that smaller dynamic range over a large range of brightnesses. It's just that if the scene is bright, and the camera is adapted to see that well (small aperture, fast shutter speed), then it won't see dim things as well as a human eye (physically there, viewing them in person) would. Similarly, if the scene is dark, and the camera is adapted for that, it will be overloaded by bright light, while a human eye wouldn't be overloaded as much. But I'm envisioning this as being a dim scene with not-very-bright laser beams, so it might be okay.)

author: james_s
author_rank: Super Contributor
timestamp: October 30, 2018, 02:26:46 am
content: Even a hugely powerful beam won't be visible unless there are particles of something in the air for it to illuminate. Once you get up to several tens mW normal room dust is enough to make a beam visible but for a really good effect you'll probably want a very light haze from a fogger or hazer in the room.