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An optical accessory option question.


Well-known member
Jun 3, 2007
How so? Can you make just one of the lenses do the same job as a pair? It seems the first lens expands the one axis and the other collimates it. Unless you are talking about a totally different lens.
The intent in pairs is to circularize a beam (collimation can be done too). My intent is to tame the fast axis to achieve a square or square(ish) beam vs the rectangle normally seen. I do think it would work. I've looked for experimental grade C lenses but not found any to test the idea.

If you're taking part in that C lens group buy test out the idea if possible.
Last edited:


Well-known member
Sep 12, 2007
One lens works fine in (at least) two scenarios.

1) provided it has a very long focal length. You see, the axis is already diverging, just not as rapidly as with concave assistance. Say it diverges to a square after 40cm. If a 40cm focal length lens is placed at this location, the beam is re-collimated at this diameter. I've done this myself.

2) provided it has a very short focal length, and is small enough to fit on the die facet. This causes one axis to diverge faster, so the beam is roughly square by the time it hits the main collimating lens. This is what most people mean when they say FAC.