ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  
Pages: [1]   Go Down

Author Topic: Laser pointers & Rear Projection  (Read 8749 times)

Don Boone

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 782
Laser pointers & Rear Projection
« on: April 03, 2006, 08:48:21 am »

Since laser pointers not surprisingly just shoot right through a rear projection screen they really don't work that well. I've considered looking for more powerful laser pointers but I'm a little concerned about how dangerous an effective LP would be.

Any bright ideas?

Don Boone
Logged

Michael 'Bink' Knowles

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4279
    • http://www.binkster.net/index.shtml
Re: Laser pointers & Rear Projection
« Reply #1 on: April 03, 2006, 12:16:50 pm »

False. Laser light and projector light both appear at the translucent rear projection screen because the screen surface scatters nearly all of the light that hits it. No difference between them. Have you ever seen the laser dot shine on the wall with the rear screen material between the laser and the wall? Not when the rear screen is positioned out in the room for the gig.

Your problem is probably a small dot coupled with a weak laser. If you get a stronger laser and/or one that puts a spread on the beam to make a larger dot then the visibility goes up. I've never seen a laser meant for pointer duties harm a surface.

Best results I've seen to date involve a green dot instead of red. Green laser is so much easier to see on a rear screen surface.

-Bink

Logged
Michael 'Bink' Knowles
www.binkster.net

Mac Kerr

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 10223
Re: Laser pointers & Rear Projection
« Reply #2 on: April 03, 2006, 12:32:09 pm »

Michael 'Bink' Knowles wrote on Mon, 03 April 2006 12:16

False. Laser light and projector light both appear at the translucent rear projection screen because the screen surface scatters nearly all of the light that hits it. No difference between them. Have you ever seen the laser dot shine on the wall with the rear screen material between the laser and the wall? Not when the rear screen is positioned out in the room for the gig.
Bink, laser pointers are significantly less bright when used on the front side of a rear projection screen. An RP screen is a transmission screen, passing most of the light through it. So called high gain screens transmit more of the light, with a reduction in viewing angle. High diffusion screens are less bright, but have greater viewing angle. A front projection screen is a refllection screen, sending most of the light back out into the room. More of the laser pointer's light passes through the RP transmission screen, and more is reflected back with the FP reflection screen. It is very noticable when you use a laser pointer on an RP screen, and then look at it on the wall.

Mac
Logged

Don Boone

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 782
Re: Laser pointers & Rear Projection
« Reply #3 on: April 03, 2006, 01:37:14 pm »

I tracked down a green laser pointer that I'm going to get the customer to buy direct on a 15 day trial period.

And I wasn't worried about the laser damaging something like the screen (which would be some serious laser) but rather the chance of a careless presenter injuring someone in the audience. BTW this is for a installed system.

Thanks

Don Boone
Logged

Michael 'Bink' Knowles

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 4279
    • http://www.binkster.net/index.shtml
Re: Laser pointers & Rear Projection
« Reply #4 on: April 03, 2006, 02:04:04 pm »

Mac Kerr wrote on Mon, 03 April 2006 09:32

Bink, laser pointers are significantly less bright when used on the front side of a rear projection screen. An RP screen is a transmission screen, passing most of the light through it...


Right. The light passes through but is scattered depending on the nature of the screen material. The solution is still a larger dot (which is hard to find), a more powerful laser and the color green. Green at 532nm is thirty times more visible as deep red diode lasers at 670nm with the same power applied; ~5 times more visible than bright red diode lasers at 635nm. (Diode lasers are the cheapest kind--most likely to be found in a laser pointer.)

The US FDA limits general usage laser pointers to 4.99mw power level. 5mw and up you'll need to apply for a variance. Here's a European model that pushes into that higher range.
15mw, 532nm green, 1.2mRad divergence, 2x AAA batteries.
http://wickedlasers.com/products.php?content=basic

I recommend a 4.9mw green laser pointer for most AV purposes. Applying for a variance is more trouble than most people need.

-Bink
Logged
Michael 'Bink' Knowles
www.binkster.net

Ken Freeman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2119
Re: Laser pointers & Rear Projection
« Reply #5 on: April 03, 2006, 05:11:17 pm »

In the real world, most lasers hit the screen at an angle, especially when using RP as the users is usually off to one side.  If you think about how a screen works and the in phase nature of a laser light....yeah it works just fine if you can find one bright enough.  We too have found the green ones to be more effective than red.  

I still think it's a bad idea and I like the smart screen solution much better.

http://www2.smarttech.com/st/en-us/products/

Very cool as they interact with PPT and others.

Ken
Logged

Mac Kerr

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 10223
Re: Laser pointers & Rear Projection
« Reply #6 on: April 03, 2006, 05:40:19 pm »

My point was not that laser pointers don't work on an RP sheet, only that they are much dimmer than on an FP sheet. If there was no reflection from an RP screen, it would appear black, and you wouldn't be able to see the video on the back of it, which you can. Laser pointers work much better on front projection screens, no matter what the wavelength.

Mac
Logged

Ken Freeman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2119
Re: Laser pointers & Rear Projection
« Reply #7 on: April 04, 2006, 12:20:27 pm »

Its all good....AS I noted before, its not right, but it is what people do...
Logged
Pages: [1]   Go Up
 

Page created in 0.03 seconds with 20 queries.