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08-10-2016, 02:21 AM #33
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steve001
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

Quote:
 Originally Posted by Alaskan I've wondered how far I can converge a beam to a small point using a 12 inch diameter lens, but haven't dived deep enough into the formulas to find out. I was able to get through an intense electronics degree program using math approximations, but since then, haven't had to use much of it again.
In the manner you've asked the question the diameter isn't important. The focal length is.

08-10-2016, 03:14 AM #34
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

I should have wrote PCX lens if the flat side faces the outside, same issue, FL? What is the best lens for a beam exander, a aspherical lens? I've read a post where the lenses in order of best are: 1. Aspherical 2. PCX 3. Bi-convex. True?
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08-12-2016, 02:37 PM #35
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steve001
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

Quote:
 Originally Posted by Alaskan I should have wrote PCX lens if the flat side faces the outside, same issue, FL? What is the best lens for a beam exander, a aspherical lens? I've read a post where the lenses in order of best are: 1. Aspherical 2. PCX 3. Bi-convex. True?
Link to that post please. I been looking into your question it's one that i have asked myself. I've not found an answer. I suspect it may not matter at all. I think for our purpose of creating a low diverging beam using lens that are easily mountable would be pcx and double concave or PCB lenses. The important thing to keep in mind is one lens should have as short a negative focal length as practical and the positive should have an appreciably greater focal length. For example : use a -6mm and 30mm would give a 5x expansion.

08-12-2016, 03:20 PM #36
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

I found the original post, did a cut and paste:

Quote:
 Krazer: It of course depends on your application, but for an application where you are taking a collimated beam and focusing it to a spot (as would be used for a telescope or diode collimator), a bestform will outperform a plano-convex which will outperform a bi-convex. You can do better with a doublet (such as an achromatic lens), and for monochromatic light you can always do the best with an aspheric lens. The difference between a bestform or achromat or ashpere has to do with the level of optimization applied to the lens design. When designing a plano-convex lens your only degree of freedom (for a given focal length and optical material) is the lens thickness, and for almost all applications it works out that the thinnest possible lens will perform best. When designing a bestform lens the lens maker has 3 main degrees of freedom, the curvature of input/output faces and the lens thickness. When designing an achromat you have even more degrees of freedom, there are the input/output curvatures of each optical element, the thickness of each optical element, the spacing between them, and the material they are each made of, which allows the lens maker even more freedom. With an ashpere the lensmaker is no longer constrained to using spherical surfaces, so there is a virtually infinite number of degrees of freedom (a typical asphere will have about 10 coefficients that determine the shape of the surfaces). You can try playing with OSLO (a limited edition is free for students) http://www.lambdares.com/oslo-university-program which will directly give you plots of the lens performance for different optical designs.
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To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

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08-12-2016, 04:59 PM #37
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steve001
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

Quote:
 Originally Posted by Alaskan I found the original post, did a cut and paste:
Ok. So it would appear that a pcx lens would be the first choice for use in a beam expander, since the goal is to produce a beam of lower divergence and it's easier to mount.

08-13-2016, 02:25 AM #38
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Re: Question for the optics savvy in regard to beam expansion to reduce divergence.

If you want a very large fairly inexpensive collimator for a beam expander a PCX lens is the way to go, but I'd prefer an aspheric lens if I could find a large three inch diameter one with 1/4 wavelength accuracy to its curve, not finding them.

I like my beam expanders to have a collimator lens with several inches diameter.
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RHD's Relative Perceived Brightness Calculator. Compare brightness @nm: http://lsrtools.1apps.com/relativebrightness

To shorten my signature I have moved most of my laser related web links to this forum page, the second post in that thread shows most of my builds... Alaskan's Laser Links: http://laserpointerforums.com/f44/al...ml#post1449395

Sincerely investigate any of these three short quotes as new concepts and you've taken your first step into a larger world:

"I regard consciousness as fundamental. I regard matter as derivative from consciousness..." - Max Planck. "Everything we call real is made of things that cannot be regarded as real" - Neils Bohr. "What we call physical things and events do not exist independently of subjective experience..." - Deepak Chopra.

Each of these three rabbit holes go deep, ending up in the same place.

Useless troll fighting.
.........................
http://imgbb.com

High resolution of my avatar: https://ibb.co/fWOhXF

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