I absolutely agree with the moderator... You must ensure that your source of air is clean. This doesn't mean that you replace the compressor, but you do need to clean the air. I know that the lenses are expensive. It would be a great investment to add an oil/water mist seperator and maybe a hepa filter. Make sure to use a spin type seperator (not a desicant type). I also recommend that you use an auto drip style also. Also make sure to match the volume of air flow to the size of the spin seperator.... Too much or too little air flow can stop the seperator from working efficiently. After the spin filter.. use a small micron filter.. check it often and replace it when it gets clogged.
This might sound somewhat complicated, but it will save you lots of time, money, and headache with the laser lens.
Ray Scott
www.scottware.net
3503 Carol Ann Lane
Middletown,OH 45044
laser machine sales in the USA