Question about focusable lasers?

[rpaloalto]

I was wondering, if in general. Are focusable lasers. More prone, to having poor divergence?
I just got my second rayfoss 532nm laser. When shining on a wall close by. The dot size looks great. When you try and shining it in other rooms the dot size becomes very large and oval. Shining on the house, across the street. The dot size. Becomes very large. Looks like a flashlight.
The last 532nm laser from rayfoss was no were as bad. However it was allot worse than my cheap 532nm 15mw non focusable laser.


If any body has been following my posts about rayfoss. You will know I have had some trouble with their quality but not their service.

The first laser died on me.

The second laser was mod hoping. So I decide to take it apart and see if I
could adjust the pot. To decrease the power. I scratched the lens when putting it back together. I ruined it. So I bought another one.

This is the third laser. The divergence sucks. I'm so pissed right now. I don't want to send this one back. I don't even want to tell faona from rayfoss. She has been very nice to me.

 

[nikokapo]

I don't really use the "divergence" term when using a focusable laser. Only when focusing it to infinity you can measure its divergence.

Take it like a full cone (not the half cone, full cone. i.e. x^2 + y^2 - z^2 = 0). It starts fat and starts getting narrower and narrower until it reaches a "waist" where it starts to get fatter and fatter again.



If you're having problems with a company contact them right away. This is a great opportunity for Faona to show LPF her customer service quality.
If you can verify the divergence is higher than stated then send it back.

 

[daguin]

All light diverges. You can imagine the light coming out of your laser as a two-dimensional "X" lieing horizontally. When a laser is "focused to infinity" (like most green pointers) it is focused so that the focal point (the "center" of the "X") is a far away as possible. That way the beam appears to not get any thiner or fatter. It does, but it is a long skinny "X". The beam converges toward the focal point at a shallow angle and so leaves the focal point at that same shallow angle. The beam gets fatter, but does so at the same rate as it got skinnier.

When you "focus" a laser up close, you creat a short fat "X". The beam 'converges" at a steep angle toward the focal point and so leaves the focal point at that same steep angle. It gets "biggger" much faster because of the angle.

Of course the light from the laser is a "cone" (like an hour glass), but you can visualize the process with the two dimensional "X"

Peace,
dave

 

[nikokapo]

Daguin's explanation is a better approach. The hour glass example was great I'm too math/tech for this stuff

If you still have the focusable laser you can see it for yourself. During night take your laser out and start playing with the focus and you'll see the cone we're talking about.


More info here:

Geometrical optics - Wikipedia, the free encyclopedia






Damn this gif is cool:

 

[rpaloalto]

I do understand that the light emitted. Is not just one continues focused beam. It has to expand. In order to compensate for this expansion. The beam is slightly focused inwards upon it's self. This allows the beam to reach great distances.
But this one shining across the street is a huge dot. Shining down and across the street it is a big, 8 to 12 inch scattered blob of light.
This is just like the first one. Using the focus ring. Would give me a dot from big to bigger. No mater how far or close I was to a particular object.

 

[nikokapo]

I do understand that the light emitted. Is not just one continues focused beam. It has to expand. In order to compensate for this expansion. The beam is slightly focused inwards upon it's self. This allows the beam to reach great distances.
But this one shining across the street is a huge dot. Shining down and across the street it is a big, 8 to 12 inch scattered blob of light.
This is just like the first one. Using the focus ring. Would give me a dot from big to bigger. No mater how far or close I was to a particular object.

That's because the lens is too far away from the diode. Are you using an external lens besides the internal one inside the module?

 

[daguin]

If you cannot get it to focus closer then it is broken. Have you tried turning it farther in BOTH directions?

Peace,
dave

 

[rpaloalto]

No I'm just using the laser as is.
I already took the head off. To see if I could bring the second lens closer to the module. It seems it's is as close as it's going to get.

 

[rpaloalto]

If you cannot get oit to focus closer then it is broken. Have you tried turning it farther in BOTH directions?

Peace,
dave

Yes I have tried turning the ring back and forth at different distances. Anything
over 40ft is just a big dot or even bigger dot

 

[nikokapo]

Could you take some pics of the assembly + other stuff you're using? We might see the problem with them..

 

[rpaloalto]

Here is the rayfoss laser
Rayfoss

This is about 6 ft

These are about 20 ft
Smallest and biggest focal point

You can see from this distance. That anything beyond 50 ft or more. Is going to look pretty bad.

 

[nikokapo]

Are you sure that lens doesn't go in anymore?

 

[dr-ebert]

As a rule-of-thumb, with a 1mrad divergence, you'll get a dot size of x mm at x m distance - of course this is only the case for distances >> 10 m or so, since at lower distances, the initial beam diameter and focusing will play a major role. (Determining the dot diameter is also not trivial, as it's not sharply bounded.)

Without a beam expander, you won't be able to get below ~0.5mrad. Greens are usually sold with a spec of "divergence<1.5mrad" or so. So, 1mrad is a very good ballpark figure of what you should get - at that divergence, the beam reflection from >10m away should look like a "fat" point (i.e. just barely not a starlike point).

IF you've focused your laser properly to infinity (i.e. point at something a few dozen meters distant and turn the focusing ring until the dot is as small as possible - use glasses to watch the dot and make very minute, careful adjustments), then there clearly is something wrong.

 

[rpaloalto]

Their is something wrong with this laser. With my o-like dilda, and my blue ray, from RA_pierce. I can achieve much better focusing. Their is a middle point when focusing. With these, other lasers.
Their is a middle point were the beam will begin to go in the opposite direction. Big to little. Then back to big.
With this laser it just goes from small to big. With the smallest not being very small especially at distances.

I will contact faona. and see what she says.
I know rayfoss has excellence customer service. I just think that I might be expecting to much. $150 for a 200mW 532nm laser. In a big heavy host is not allot of money. Sure it's a few dollars more than kidomain or focalprice.com But, you do get very dependable care and service.

 

[nikokapo]

I don't know what is happening, I can't tell you anything else than to play with the focusing ring but it seems you've already done so. Contact Faona, please.

 

[LarryDFW]

rpaloalto;

I have the same laser in a 50 mw power.

The factory focus point is not always optimum.

Look at my post:

http://laserpointerforums.com/f45/greens-can-indeed-burn-41833.html

The final focus lens is factory set for a parallel beam.

In my post I talk about changing the factory focus point.

Are you checking the focus thru goggles ?

That is the only way to see the actual beam width.

LarryDFW