DIY Beam Expander

Just wanted to know, has anyone made a DIY Beam Expander or does anyone on LPF build and sell one. I would like one for my BRD using the Galilean principle in stead of the Keplerian.

Galilean, to me would be easier for me to build and the lens are a little cheaper from some sources I have found. Plano-Concave and Achromatic lens are used for the Galilean BE. Beam Expanders are available on the web but are very expensive. I figured that Jayrob may have tried this, but I could not find a thread for beam expanders. Any help would be great.

:thanks:

Tymtravler;

I have assembled a "Galilean type" on the bench.

I used some Minolta 25mm diameter plano-convex lenses for the expanded beam.

The mounting for the lenses is the difficult part.

LarryDFW

Well don't keep me in limbo, how did it work, got any pictures. What was the diameter of the Achromatic len, inquiring minds want to know. What type of diode did you use??:thinking:
Tymtravler

You don't need an achromatic lens for a (monochromatic) laser. You may need an aspheric one.

Interesting, most documentation and the diagram of the thumb nail on my first post on this thread shows a Plano-Concave and Achromatic lens. If you know of a better way using a Aspheric one please let me know:thanks:
Tymtravler

The diagram must have been created in the close proximity of a black hole, the way those light paths bend

An achromatic lens (partially) compensates the fact that the diffraction index is wavelength-dependent, so beams with different colors have different focal points (chromatic aberration); this is always done by combining concave and convex lenses made of different materials. With a laser, you only have one wavelength, so this is not an issue.

An aspheric lens compensates for the fact that with a normal spheric lens, light beams travelling close to the center will have a different focal point from beams hitting the lens nearer the rim (spherical aberration). The effect becomes significant with lenses that have a high numerical aperture (NA), i.e. when their f/ratio becomes small; that's why the collimating lenses are "aspheric".

If you don't use short f/l lenses, you can forget about that as well. Start simple and see how it goes.

EDIT: Ignoring those really weird light paths in the top diagram, it would be correct if you wanted to build a telescope.

EDIT2: And this should have gone into the Optics or Experiments section, not B/S/T...

Hey thanks for the great info, it helped alot. However I put this in B/S/T if you read my first post, I wanted to know if someone had built one or had one for sale that they built. So many optic items are built by forum members and sell them here I figured this would be the best place ask. Forgive me for my stupidity.:undecided: