Hello everyone! I'm new to this forum, although I've been reading it for a couple of days now. I recently received a 125 mW green pointer from dragonlasers.com, and I was wondering if anyone knew the true range of the beam. I saw a chart that said 50 miles, but I highly doubt that. Has anyone ever done some extensive testing? I do admit that the beam does seem to go on endlessly when I point it into the night time sky. Thanks for your help guys.

P.S. The specs are as follows.

Beam Diameter : 1.2mm @ aperture
Beam Divergence : <1.2mRad

Use math, it can help you

Then what's the formula to calculate it?

Is this out of curiosity, or do you need to know for something?

It doesn't really matter, because of the beam you wouldn't be able to distinguish the dot from 500 yards away. There really isn't a math equation that will be exact; there's a lot of different factors that will change it (altitude, fog, etc.).

And when they say 50 miles, they mean if you look into the laser from that far away, you'll see the tiniest bit of green light. That's how rediculous the rating are. =P

id say a good 30km with a telescope.

Well, I must admit that that is ridiculous. It was just out of curiosity. I doubt you'd see anything @ fifty miles due to the curvature of the Earth and what not. But man, that's truly amazing. Thanks for your help.

It can reach 50 miles in absolute darkness with no obstacles.

I also noticed that when I point it into the sky, the beam seems to stop after a certain distance. I'm sure this is some sort of illusion, but would anyone be able to explain the reasoning to this? Or is that distance really far away but just looks closer than what it really is.

Well for my part i notice it stop on the clouds when i see a dot on them.. and thats when i wasn't using beam expander .

Pardon my butting in. I have read that the 'range' is infinity in theory. On Mythbusters they aimed a mega bright green laser at a reflector on the moon and were able to detect(but not by eye) the reflection. Some one should set up some cameras aimed at low clouds ( no curve of earth issue) and do comparison with red-green and blue gas and solid state lasers. ---hak

Well 50 miles is kinda pointless because of the horizon is like 5 miles isnt it?

The horizon is about 3 miles but you have a visual range much greater than that. Depending on the height of the object you can see well past the horizon.

Distance to the Horizon

Jon

I have a church, with the front painted white, distant 1600 meters from where i live, and perfectly visible, cause it's on a mountain ..... i use it all the times, when i have to focus something

Placing the laser on a holder, and using a little telescope, i can see also 5mW of red, on the white front, but only at full night , and perfectly focused ..... my old, abused, 50mW green pointer pen, instead, i can see the spot at cloudy day (but not in full sun) also with bare eyes ..... ok, ok, using a church as a collimation tool, risk to make me discommunicated from vatican for blasphemy ..... but it's all that what i have at hand, for this

we are receiving light that is 14.7 billion light years away from us. and that is because any time before that is registered as the age of darkness and before that the big bang. Theoretically, this light (laser) should travel just as far if it has no matter to absorb it or deflect it

BTW..... to the forum...


Jerry

The range of a common laser pointer was discussed starting here. Short summary: you could easily see them on the ISS 1000km away and possibly up to around geosynchronous orbit. That's pointing more or less straight up in a clear sky, pointing them horizontally you'd get a lot of absorption and scattering in atmosphere that would greatly reduce the range.

When you point the beam at the sky, it actually "stops" at infinity, the point where your eye and the laser beam are aligned in parallel - like the point where the two sides of a railroad track converge. The beam seems to have more or less equal brightness all along because the farther away the beam, the more foreshortened you see it, so the attenuation by distance is compensated.

Laser reflectors have been placed on the moon by the Apollo astronauts 40 years ago; they've been used since then to measure the moons distance with cm accuracy. However, it takes a powerful (pulsed) laser aimed through a telescope (beam expander) at the moon and a 2nd big telescope to see the return pulse; after all, the reflector only has a size of a couple of square feet and intercepts (and reflects) only a tiny amount of the emitted light - and the receiving telescope only gets a tiny part of that. I guess it's only individual photons that get received.

Thanks a lot guys for your help, you all rock! I had a feeling it had to to with being parallel dr-ebert, but I wanted to be sure. I'm just too curious. Anyhow, I'm going to Hawaii in a week from today, and when I get back in three weeks I am going to try to construct a blu-ray pen laser. I bought one in an aixiz module from ebay with a rather big driver, but i fried it like a fool lol. I'll let you all know how I make out with that in about a month or so. Thanks again guys!