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ArcticMyst Security by Avery

Aha! Found how to best focus an IR beam to infinity, sharing the idea.

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Jan 29, 2014
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I've had some suggestions given to me in the past from LPF members regarding how to focus an IR beam you can't see to infinity which I found to be too cumbersome for me, but believe I just stumbled upon a much easier way:

I found when using a 75mm dia. PCX cylinder lens in front of the output of a large 67mm diameter collimating lens, when the laser is focused to produce the thinnest fine line possible without blurred edges on a distant wall the beam is then closely focused to infinity, the further away you are with the setup from the wall, the finer you can adjust the focus to infinity. Of course you don't need to do this to focus a visible laser to infinity because if the beam is visible, you can just look to see when the beam is as narrow as you can adjust it to be without any waist in the beam. However, this method is probably the easiest way to adjust the beam to infinity when using an IR video camera to observe the changes. This method works well with both small laser spots of just a few mm diameter or large spot beams to find infinity focus.

Thought I'd share this in case someone else has been scratching their head on how to adjust an IR laser pointer to infinity for a long time, as I have.
 
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