Adjustable Beam Divergency - HOW??

As we know increasing the beam divergency will make shows lasers saver to watch.

How can we as laser hobbyists increase the divergence to make the laser more save to watch.

I have also seen laser with adjustable beam divregence between 1 - 10 mRad. this option would be great for savelij watching the laser in smaller area like a living room.

I hope someone comes up with a cheap and simple solution.

Maurice.

The cheapest way is simply to place a negative (-) spherical lens in front of the output aperture of the projector. You could try a -2.00, -4.00 or -6.00 diopter lens depending on how much divergence you require.

Probably the best place to easily lay your hands on these lenses is your local Optometrist/Optician/Eye Doctor. If you have a 1 hour Optical Lab in your area just ask them to sell you an uncut lens. These are usually around 70mm diameter, they may also have lenses that already have a multi anti-reflection coating applied. I doubt you'll easily pick up glass lenses nowdays, but the plastic ones are just as good.

Cheers

Jem

P.S. Why don't you fill in your profile, or at least give an indication as to where in the world you are?, who knows, I may be able to help you with your quest :)

This lens from allelectronics seems to work pretty well. Place it in front of your scanners (so you're scanning through the lens) and after just 20 feet the beam will be around 3 inches in diameter.

Best part is that it only costs $2!

Adam

PS: Note that I'm not advocating this to be used for a commercial audience-scanning projector! Diverging the beam is just 1 small part of the solution. But if you want to increase your safety factor when viewing your laser shows in your home, this is one way to do it.

Adam

That's a conVEX lens. You're really better off using a conCAVE lens.

A concave (or negative/minus) lens will diverge the beam without it being focussed first. With a convex lens the beam will be focussed to a point before it diverges.

I'm not saying it won't work but I don't like anything in front of the aperture that focuses beams ;)

Jem

Quote:

---

Originally Posted by Jem

That's a conVEX lens. <snip>With a convex lens the beam will be focussed to a point before it diverges.

---

I know. That's one reason why I said not to use it for audience scanning.

However, in fairness, the focal point is *very* close to the lens - within about 8 inches or or so. So unless you have a habit of looking into your projector from 1 foot away, you should be OK.

The real appeal is that it's so cheap. Double-concave lenses are expensive. (At least, the ones I've seen are.)

Adam

Quote:

---

Originally Posted by buffo

I know. That's one reason why I said not to use it for audience scanning.

However, in fairness, the focal point is *very* close to the lens - within about 8 inches or or so. So unless you have a habit of looking into your projector from 1 foot away, you should be OK.

---

Fair point, but some people do silly things :rolleyes:

Quote:

---

The real appeal is that it's so cheap. Double-concave lenses are expensive. (At least, the ones I've seen are.)

Adam

---

They don't really need to be Bi-Convex, however, if you need anything like this just PM me ;)

Jem

I think its also Possible to place a small piece of lens just in front of you scanners. or not?
Maybe even remote controlled so you can have a swith on your projector:
For example:
Big projection room Off - 1,5mRad
Small projection room On - 10mRad

get two ar coated convex lenses either a pair of 15 mm FL or a 15 mm FL and a 30 mm FL, and adjust the distance between them. You should find what you want :-)

cheap lenses

www.surplusshed.com

use the lensfinder java

Steve

To be honest, I'm really surprised that no-one has come up with a lens that automatically moves in front of the beam via a DMX or ILDA control command.

After all, graphics demand tight beams, beam shows are best with fat beams, and many projectors are used for both even within the same show.

Surely it would make sense to have a lens inside the projector that could move into the path of the final beam within a fraction of a second (or retreat) to turn the laser instantly from fat beam to narrow beam or back. When you look at modern opticians equipment these days, the optician presses a button and lens of a pre-selected power zips into place (I'm presuming there's some kind of wheel system bit like for diffraction gratings allied to a precision stepper motor). Would it really be so hard to have a plain lens for graphics and a convex lens for beam shows on a small wheel and have it turn one way or the other quickly via a precision stepper in a projector?

While there are couple of ways to do this automatically. General scanning made a scanner based focuser that you could adjust with each dot position. And people have also made deformable mirrors that would do the same thing.

but mixedgas has the right idea.

chad