Or just get diffraction gratings. No need for the silly "glasses" markup, you know the number of lines per millimeter, and you can get 25 of them for around the

Or just get diffraction gratings. No need for the silly "glasses" markup, you know the number of lines per millimeter, and you can get 25 of them for around the same $10 http://www.amazon.com/gp/offer-listing/B00K6K3MCW/ref=sr_1_1_olp?ie=UTF8&qid=1443337421&sr=8-1&keywords=diffraction+grating&condition=new http://www.amazon.com/gp/offer-listing/B00K6K3MCW/ref=sr_1_1...