- Jul 24, 2007
Thanks Pseudo, that makes things much clearer
Its possible, but can get expensive. I'm guessing that's somewhere in the range of a ~20-50x beam expander? You could buy one from a real optics joint, but it would be expensive as hell. One problem is that means you need at least a 50mm lens, and it would be wise to use a lens larger than the beam passing through it. If you wanted to go the DIY route though, you'd need a strong diverging or converging lens, and a large, weak, converging lens for the job. Check out the pictures above, one of them demonstrates the setup, and the formula that: |focal length of the second lens| / |focal length of the first lens| = how many times the beam will be expanded.Stone said:Since this topic is explaining basically what I would like to know, i'm going to ask in here...
I'm looking at expanding a beam as well, but from a basic laser pointer size beam (a Aixiz 650nm 10mw 12mm X 30mm case with a DVD burner diode) up to 40-50mm in diam. if that is possible. Is there expanders that would expand that much or is there some other way of doing it?
Stone said:I have been using the formula above in the picture to estimate the lens I require... Since I can estimate the input beam diam, output beam diam, and the secondary lens I can rearrange the formula to work out the FL primary lens I need.
Since the output is d and the input is (f2 / f1) * d, I can call the input "y"... So I need to know f2.
y = (f2 / f1) * d
y / d = f2 / f1
(y / d) * f1 = f2
f2 = (2mm / 40mm) * 35mm
f2 = 0.05 * 35
f2 = 1.75mm
That seems like an unrealistic focal length for an aspherical or concave lens like in the above diagrams... Or is it possible?
Your not going to find any off the shelf lenses that will do that. It is highly unlikely you'll find a lens with a focal length < -6mm. It seems worldwide that -6mm negative focal length lens are the most common. And I must add to have a 4-5cm beam spread within 3.5cm would require multiple negative lenses.I was looking at this (I can't posts links - But it's a 50mm diam/35mm FL aspheric lens) to converge the beam after it had been spread, I just couldn't find anything that seemed suitable to diverge it though. The diverging lens needs to be able to spread the beam from it's original diam. to 40-50mm within the 35mm focal distance of the 2nd lens.
In the two top boxes input 0.14Stone said:Thanks for the replies... It looks like I might have to resort to making my project a bit longer to keep the cost and availability of the lens easier to work with.
If we disregard my length limitations, is there any common and cheap lenses that would work for me? The only store i've looked at is Surplus Shed as their lenses seem quite cheap.
If I was to use the common -6mm FL lens mentioned, i'd need a 120mm FL secondary lens, that's 126mm between 2 aspheric or 114mm between a concave and aspheric. My secondary lens MUST be 50-52mm in diam.
Steve... I don't understand that beam program, just due to not knowing the terms "separation length" and "Rayleigh range", but I can do a search
I've been Googling lens suppliers and i've found many small 2-3mm FL lenses from various suppliers but the prices seem rather expensive. As this is just project has no real use other than me wanting to make a wide beam, I don't really want to spend a fortune on it.