Laser with the longest throw for $300

[Solomon MK2]

Hi,

Don't know much about lasers. Just got my first (luckyduck, from dr_lava) last week, and now I'm thoroughly addicted.

I was just wondering... what is the longest throwing laser out there & for around the $300 mark. Also, how far will the laser throw?

Thanks all.

Solomon

 

[ACMarina]

If I'm not mistaken, even a 5mW laser can throw farther than you can see..

 

[Solomon MK2]

I'm not sure I agree with that...

You see, I was out tonight, just shining it out at the sky, and I could definately see the end of the beam. Also, I drove out to a lake (where there are trees and wilderness on the other end, about 3.5km away) and I couldn't even see end of the beam). It just dissapears.

I tried shining it on a lighthouse about 10 - 12 km away (the beam is quite visible where I was), and I couldn't even light up the lighthouse, even though it's white.

I was both exhilirated and slightly dissapointed.

Does anything have mega range for the price I'm looking at???

Solomon

 

[bg2vo]

1km if we are talking about seeing the bounced light. May be more if you have more power. May be less if its not very dark.
All laser disperse. At 1km the light will be scattered into a 1.5m circle.

 

[comozo]

I'm not sure I agree with that...

You see, I was out tonight, just shining it out at the sky, and I could definately see the end of the beam. Also, I drove out to a lake (where there are trees and wilderness on the other end, about 3.5km away) and I couldn't even see end of the beam). It just dissapears.

I tried shining it on a lighthouse about 10 - 12 km away (the beam is quite visible where I was), and I couldn't even light up the lighthouse, even though it's white.

I was both exhilirated and slightly dissapointed.

Does anything have mega range for the price I'm looking at???

Solomon

You see, I was out tonight, just shining it out at the sky, and I could definately see the end of the beam.

Wow you are a novice by not knowing light continues to travel unless stopped by something. They all have mega-range What you saw is an optical illusion.
The beam of a 5mw pointer outputs too little light to have enough light to reflect back from a matt surface that reflects little. Shining your laser onto a mirror or reflective white street sign will produce results. There's atmospheric scattering to consider also. Beam Divergence also matters.
Throw can be increased by lowering the beam divergence. I lowered the beam divergence on my 26.3mw pointer to around 0.19mrd and increased the throw to about 8665.464m, but I have to use a 30x by 50mm spotting scope as the spot at that distance on a matt white surface is to small to see using eyesight alone. I can't answer your original question I can only say this, buy a green pointer of the highest output available at that price.Here are some links you'll find interesting.
http://www.g0mrf.freeserve.co.uk/laser5.htm
http://www.earthsignals.com/Collins/0036/

 

[Solomon MK2]

Wow you are a novice by not knowing light continues to travel unless stopped by something. They all have mega-range What you saw is an optical illusion.

You are right, light continues to travel. But to be totally honest, it's not very useful if the light in question is of the "invisible" type.

 

[dr_lava]

Hi there solomon, also, he's right about spot size being too small to see and the amount of light being reflected back to little due to atmospherics to pick up with your eyes. If you have someone else standing that far away, they will be able to see the dot on the white surface next to them if you put the laser on a still tripod or similar. Also remember that in order for you see a dot at the end of the beam, the surface has to reflect enough light back to you to be brighter than the beam itself that you see! Otherwise no terminating dot will be visible. This is best observed with low lying clouds on a clear night sky.

 

[Solomon MK2]

Hi dr lava,

Thanks for the nice laser!

Admittedly, I guess this is just an excuse for me to purchase a more powerful laser. Yours was my first laser, and I was amazed and overjoyed with the thing. I've had tons of fun with it.

Then it occurred to me. Imagine what a $300 laser would be able to do??! You see, (indirectly) my girlfriend got me involved in this. She's an astronomy buff and I read about green lasers in a magazine she subscribes to. I was a little sceptical at the time, but now that her birthday's coming up, I decided to buy one.

I'm sure she'll be thrilled with whatever I get her (she hasn't seen a green laser up close, either!) However, I would like to get a laser for myself as well, that way, I have an excuse to spend more time with her.

Solomon

 

[dr_lava]

Here's something I've been meaning to do.. Answer the question "how far can we see the beam extend?"

Let's say that you're looking to see the beam on your new laser, and hold it out 1/2 meter from your eye and look down the beam 2km away. The last 50 meters (1950 to 2000) appear to your eye as a 12.5mm bar almost 2km away! I.E. you can't see it.

So, how far CAN we see the beam? The eye can resolve, in a relatively low-contrast situation as this, about 2 arc-minutes. (2/60 degrees)

In our mentioned situation, this works out to be the last 1400 meters of beam. Thus, When we point the beam out, we are really only seeing 600m of throw without a scope, no matter how bright the laser is!

Note that this does not take into account beam divergence, which really wouldn't help see the beam much farther.

I hope this helps you understand what is going on.

the math: (feel free to check it)
deg=tan-1(0.5/2000) = 0.0143 degrees at the acute angle at 2000m away

height = 50 sin deg = 12.5mm = how long the last 50m looks at 1950 m out

ac = sin-1 (height/1950) = 3.67e-4 degrees (0.02202 arc minutes resolution we would need to see the last 50m at 2km)

solve for x:
(tan-1 2/60) = (x sin deg)/(2000-x)

x = 1400m

distance visible: 2000-x = 600m