A Guide To Buying Your First Green Laser

[JaiNobeZ]

Haha... you have a point there.

In that case I'd better make a thread about buying some other wavelength of laser and then we can have a gang-war between our noobs! Then you'll be sorry that you took the opposite side to me in one of those forum conflicts!

 

[randomlugia]

Good luck with that. They wouldn't stand a chance - green pwns all!

 

[JBTexas]

"Focusing tio infinity, and evaluating divergence".

I didn't want to waste a thread for this ... this seems like a good spot for a simple question.

Yesterday morning, at about *4:00 A.M.*, I took out my new 200mw Green Gatlin, and my binoculars (10x50), both mounted to a heavy duty camera tripod with something I rigged.

My apartment complex is divided into 2 "phases" separated by an open field (don't ask me why, I don't know, it's weird).

My apartment is at the southern edge of the complex. I targeted the Gatlin on a building WAY across the complex near the northern edge; spot was towards the TOP of the building, AWAY from windows. Then I worked the focus knob for the SMALLEST spot possible.

I have some maps of my apartment complex / area, that I printed off of TerraServer some time ago; accurate scales, grids (this was for certain amateur radio uses).

The beam path was almost exactly *250 meters* in length.

After that, I CAREFULLY moved the laser around a bit to compare the size of the spot to some objects.

The now-focused spot, at that distance, SEEMS to be *slightly* larger than the width of an automobile license plate; say, about a > foot/30cm or so. It's possible that is under-estimated, because even the TEM00 spot isn't perfectly/sharply defined, but it looks pretty good with this laser.

I marked the Gatlin with "index" marks, on the case / focus knob for this point (permanent marker covered with small squares of transparent cellophane tape).

I realize that quality varies from laser to laser, and probably even among instances of the same model... but GENERALLY, is that pretty good? Or can I / "should I be able to" do better?

Thanks.

EDIT:
Actually I just found this:

mRad:
http://www.pseudonomen.com/lasers/calculators/mRadCalculator.html

diam:
http://www.pseudonomen.com/lasers/calculators/diameterCalculator.html

... and I plugged some numbers into it. I had to guess on some things, the O-Like website doesn't provide many tech details for this laser, but I used some typical values for other green lasers.

The results seem to imply that my divergence / focus is pretty good/average for a "typical" green DPSS.

 

[randomlugia]

Was the laser shining through the binoculars? That part confused me.

 

[JBTexas]

Oops... sorry about the confusion... no, it was not shining through the binoculars.

Someday, maybe, I will learn not to ramble, and to be more succinct (doubtful, I am too old to change).

The binoculars and the laser were mounted side-by-side on the tripod, more or less parallel. I used "scrap struts" with holes in them; velcro straps, Nutz and Boltz.

I needed to look at the SPOT *through* the binoculars to better judge the size of the spot.

 

[JaiNobeZ]

That's what i thought to be the case. I know little about optics, so i'm not going to be able to answer this one. Over to you, RandomLugia.

 

[JBTexas]

JaiNobez / RandomLugia...

I think I consider the question answered; see the EDIT section of the first post; I didn't delete the post / left it up because someone may find it useful. I found those two links AFTER I put up my post.

Those laser divergence / diameter apps seem to imply that my infinity-focus is good, and that the divergence is good. The spot is about 30cm / ~ 1 foot at 250 meters. It's pretty dramatic to look at.

Only "problem" is how best to mark the infinity-focus mark. I used a permanent marker on the focus knob, and on the case, to line up the knob with the infinity-focus point. I cut little squares of cellophane tape to cover/protect the marks.

I knew the tape would probably come off, and it did. The perm marker ink will not stay on metal for very long.

So now I'm thinking to carefully etch/scratch where I want to mark the metal with a "scrap" knife, THEN fill in the scratches with perm marker.

 

[randomlugia]

The thing is, I'm pretty sure what you did was totally unnecessary. You could easily calculate the divergence with 10 feet of space, and probably even get a better measurement because you can measure the beam with a ruler or something like that.

Pseudonomen137's mRad calculator is really nice. What did you get for the divergence when you put the numbers in?

Whether divergence is "good" or not is kind of subjective. If you're happy with the way the beam stays together, great! Just because some numbers say so doesn't mean you should be unhappy with the laser. Know what I mean? Honestly if it's reasonably low, I couldn't care less what my laser's divergence is, and I really can't even tell. If you want to pop balloons at 200 feet however, that's different.

 

[JBTexas]

I don't remember exactly what I got, but the calculated beam diameter was 38.xxx centimeters at 250 meters, using generic 532nm values. Again, the 250 meters is a (good) approximation from a map, the ~ 30 centimeters was a visual approximation (through binoculars), and I used *generic* values for 532nm; there do not seem to be any exact values published for the (2) Gatlin models (100mw / 200mw).

Sorry... my post(s) were probably more complicated than they should have been. Basically, the spot was ~ 30 centimeters @ ~ 250 meters, I wanted to know if that was "approximately the best" for a 532nm DPSS laser. Apparantly, it is or is very close to it.

 

[randomlugia]

I don't remember exactly what I got, but the calculated beam diameter was 38.xxx centimeters at 250 meters, using generic 532nm values. Again, the 250 meters is a (good) approximation from a map, the ~ 30 centimeters was a visual approximation (through binoculars), and I used *generic* values for 532nm; there do not seem to be any exact values published for the (2) Gatlin models (100mw / 200mw).

Sorry... my post(s) were probably more complicated than they should have been. Basically, the spot was ~ 30 centimeters @ ~ 250 meters, I wanted to know if that was "approximately the best" for a 532nm DPSS laser. Apparantly, it is or is very close to it.

Good for you then! That does sound like really good divergence, without knowing what the measurement at the laser aperture was.

 

[JBTexas]

Just posted a couple of map images, gives an idea of what I did:
http://laserpointerforums.com/f44/list-laser-functions-65050.html#post934166

 

[randomlugia]

Wow, you're lucky to have that much space to work with! I can see why you needed binoculars haha.

 

[phoa]

great guide very useful:thanks:

 

[Amazool]

Great guide! I should have read this when I bought my first laser!
Hope it will use my next one.thanks.

 

[australialaser]

nice i love this information

 

[webvan]

Thanks for the guide. I wanted to get a green laser after going to an star watching event and I'd been trying to find solid info on whether an IR Filter was needed and now I understand better.

Might go with Ledshoppe, one 50mW and a couple of 5mW to play with ;-)

wsdeal have a ton of lasers too, didn't see them on the list. I'm planning on getting the LP734S (a red laser with a switch that I'd found at a Toyota dealer and unfortunately lost since).