| Author | Message | ||
     Rick_oleson Tinkerer Username: Rick_oleson Post Number: 912 Registered: 07-2006 Rating: N/A |
The pattern is caused simply by the distance between the 2 layers of glass where the cement has separated. The reason it kind of resembles the effect of coating is because coating works in exactly the same way, using the thickness of the coating to establish the distance between 2 reflecting surfaces. Where this thickness is about 1/4 wavelength of light, reflections are suppressed, where it is about 1/2 wavelength they are amplified, and as Glenn explained, a varying distance of separation in this very close range creates a pattern of alternating light and dark bands. Rainbow colors appear because different colors have different wavelengths and so are affected this way at different distances of separation. If you have this effect on the OUTER surface of an element, rather than in the space between 2 of them, it has to be a foreign substance coated onto the lens either intentionally or otherwise. I have a simplified discussion of lens coating on my website: it applies equally here if you substitute air space for the coating thickness, and a body of glass where I show the air in front of the lens: http://rick_oleson.tripod.com/index-166.html |