lens for red collimation

hi all
what options are there for collimating red 640nm diodes
dont want aixiz , i am after tightest lowest divergence possible
i would have gone with roithner lens27 but thats no longer available
so i am looking for a suitable replacment
thanks in advance.

You can't have both a low divergence and a small diameter of the beam. The lens27 was a short FL lens which gave a small initial beam, but with a large divergence. Other lenses such as rothiner's 7020-H lens have a high FL which produces a larger initial beam, but with a low divergence.

laser_freak said:

You can't have both a low divergence and a small diameter of the beam. The lens27 was a short FL lens which gave a small initial beam, but with a large divergence. Other lenses such as rothiner's 7020-H lens have a high FL which produces a larger initial beam, but with a low divergence.

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hi i know i cant have both, i am looking for the best of inbetween
lens 27 did the job for me giving just under 2.5x3mm@ <.8mrad
looking to find the best replacement for lens27 that gives simalar beam specs

Well, you could try the 650-G-1. http://laserpointerforums.com/f64/f...fication-fit-aixiz-25-increase-red-46332.html

I believe it has a FL of 4.02 mm vs. lens27's FL of 3.3mm. The 650-G-1 has a NA of 0.6 where as the lens27 has a NA of 0.45.

However, I don't have any experience with the 650-G-1, so someone else would have to say whether you'd get similar beam specs to the ones you stated (although the math says you should).