two questions

Two questions regarding lasers that I'd like your opinions on:

first:
1) shining two different lasers (both in wattage and color) from the same handheld position into the heavens at night, why is it that I see them both "ending" at more ore less the exact same position? Why is this? Does it stem from the fact that I just haven't compared enough different lasers? Or is this caused by the fact that one doesn't observed the "beams" from a remote enough distance (handholding them both)? That the angle from which you see the beams somehow diguises the difference in reach of them?

second question:
2) How far do handheld laser reach? I figure it it has a lot to do with colour, power and beamspread and all, but do any of you know of any thread that discusses the matter at all (I coudn't find it...)?

Lasers don't "end" abruptly. They have just reached the point where your POV and the angle you are viewing the beams at can no longer. Think of it as a triangle, something like this:

* - the beam continues on...
*
*
*
*
* - What you perceive as the "end"
**
**
*-*
*-*
*--*
*--*
*---* ------> this line is your "line-of-sight"
*---*
*----*
*----*
*-----*
*-----*
*------*
*------* - These are your eyeballs
|
This is the laser's beam

See, once you get to this "end point" the laser beam angle is so close to the angle of your vision that they are virtually the same line, so there fore, you can not see it continue to go up.

Try this, take a chopstick, and hold it perpendicular to your line of sight. You can see the whole thing right?

Now slowly rotate it until it is exactly your line of site. (you are looking at the bottom but you cant see the top.

Now, the chopstick, according to your eye, is just a dot and, if it were to continue forward infinitely, it would remain a dot because to your eyes, the rest of the beam is hidden behind the part you CAN see.

I hope that helps...

As for #2, IT DEPENDS. Many of today's lasers can reach outer space!

It all depends on conditions... If there is very little moisture in the air, your laser will go VERY far regardless. If there is, say, heavy fog, your laser will be WELL visible, but i will not travel nearly as far as the water droplets in the air will disperse the beam into incoherent light.

Hope this made sense and helped

:beer:
-Matt

janjansen said:

Two questions regarding lasers that I'd like your opinions on:

first:
1) shining two different lasers (both in wattage and color) from the same handheld position into the heavens at night, why is it that I see them both "ending" at more ore less the exact same position? Why is this? Does it stem from the fact that I just haven't compared enough different lasers? Or is this caused by the fact that one doesn't observed the "beams" from a remote enough distance (handholding them both)? That the angle from which you see the beams somehow diguises the difference in reach of them?

second question:
2) How far do handheld laser reach? I figure it it has a lot to do with colour, power and beamspread and all, but do any of you know of any thread that discusses the matter at all (I coudn't find it...)?

Click to expand...

I had a little difficulty understanding (1) but I assume you were talking about the same effect that causes very tall buildings to appear to converge more or less into a single "point" at the top. The reason is simply a matter of perspective, commonly called converging verticals.

How to Overcome the Problem of Converging Verticals - Digital Photography School

The second paragraph of the above link explains in brief what it means.

I can't honestly answer (2) as I don't know enough to say.

Thanks Matt,

your reply does make a lot of sense indeed.
Can I take it then that I would see a more distinct difference in beamreach were I to look at these beams from a distance?

Regarding the distance laserbeams reach (under variety of conditions): do you know of any graphs/tabellen (can't come up with the proper english word) that illustrate this?
Say: a 300 mW 532 laser with beamangle/lense such-and-so will leave a visible dot of such-and-such size on a white wall, 1 mile away, as seen from 1 metre from the wall?

Just curious.

Yes Trencheel,

Guess you're right, it's a matter of perspective.
I've got some lasers coming in over the next couple of months.

So what I'll do is turn 'm all on, pinpointed at the nightsky, walk away from them and then take a look at them from a distance. That'll teach them "converging verticals" to mess up my readings, right? Thing is, I live in an urban area and I don't want to draw attention too much...

I would be wary of doing that for a few reasons - attracting attention and duty cycles being the two most pressing.

I have two questions for you-- why did you NOT put your location in your profile??
see==under my name-- Im in Texas
2) why are you triple posting??- a bad habit you should break- USE THE EDIT button- add to the last post IF it is yours-

plz go back and combine those three into one- -it wil save you the embarassment from seeing later that a mod did this for you..

When needed it IS ok to 'bump' but in this thread don't do that.

BTW
NASA Left a mirror on the moon and a green laser was bounced off it and was 'seen' back to earth(not by human eye tho) in 'Theory' the beam goes on forever.

Hello there Hawzak,

having a nice evening are you?

didn't put in my location cause I didn't feel the need to. But if it satisfies your curiosity, my location is the Netherlands. You might wanna look that up. Secondly, about the triple posting, sorry if it offended you. I wouldn't want to offend someone deep in the heart of Texas now, would I? Triple posting and all.

Your answer by the way is of not much help. Merry Christmas!

I was saving my helpful answers until I saw if you took my suggestions seriously.

not offended ---
just attempting to show you how its done here. I have a laser expert friend living over there btw- how can we help you if you dont want to help yourself ??

AND why would I want to look up the Netherlands?


IF I were trying to be a dick I would say perhaps you need to look up Belguim to see how far overseas it is from the Netherlands--lol J/K

so since you also don't seem know much forum ettiquitte -- The best first post in this forum is made in the WELCOME section-as an introduction of yourself before asking for help-

& thanks for asking --yes I am having a great day.

Belgum.
Hmm, nope.
doesn't ring a bell.

But you're setting a fine example here.

Posting a lot and contributing little as far as I can tell.
Thanks for setting an example. I'll try my best.

cheers!

janjansen said:

Thanks Matt,

your reply does make a lot of sense indeed.
Can I take it then that I would see a more distinct difference in beamreach were I to look at these beams from a distance?

Regarding the distance laserbeams reach (under variety of conditions): do you know of any graphs/tabellen (can't come up with the proper english word) that illustrate this?
Say: a 300 mW 532 laser with beamangle/lense such-and-so will leave a visible dot of such-and-such size on a white wall, 1 mile away, as seen from 1 metre from the wall?

Just curious.

Click to expand...

Aaaanyway triple posting and forum etiquette aside, I will attempt to answer this question.

Graphs or tables would be redundant. Laser divergence is measured normally in the mRad (milliradians) and it would not be too difficult to calculate spot size given the initial beam diameter, divergence and distance. I think simple trigonometry would let you calculate this.

janjansen said:

Thanks Matt,

your reply does make a lot of sense indeed.
Can I take it then that I would see a more distinct difference in beamreach were I to look at these beams from a distance?

Regarding the distance laserbeams reach (under variety of conditions): do you know of any graphs/tabellen (can't come up with the proper english word) that illustrate this?
Say: a 300 mW 532 laser with beamangle/lense such-and-so will leave a visible dot of such-and-such size on a white wall, 1 mile away, as seen from 1 metre from the wall?

Just curious.

Click to expand...

The only problem is that laser beams are relatively thin so by the time you got far enough back to see the beam extend all the way up, you would have a hard time seeing the beam at all, let alone in the sky and above

Dot size depends on the collamation lens, but when a laser is focused to true infinity, the dot size is exactly the same as when it left the aperature. This is, of course, assuming your lens does not modify the beam (i.e. the G-2 lens)

Hope that helps!
:beer:
-Matt

janjansen said:

Thing is, I live in an urban area and I don't want to draw attention too much...

Click to expand...

Good Lord, that's a selfie! Btw you should touch base with your fellow Flying Dutchman and LPF member Offroadfreak8582! Vrolijk kerstfeest!:san: