I think that it was a fog layer due to temperature change, so i leave my lens case opened to reduce the fog, but it fail( I did this for a whole day). Then i try to clean the oil layer with the Tiffen lens tissue, chamois cloth, micro-fibre lens cloth, it fail again, when ever i clean the oil layer, it disappear for about 3-5seconds, and it come back again.
Finally, I try to clean it with kodak lens cleaner, it seems to works better, but after half a day, the oil layer come back again.
The oil layer is not visible without a flashlight, i tried to look through the lens with a light bulb, it's not visible too. When to flashlight is lighting the lens with a back side light, the oil layer become extremely visible, and the circular pattern will change if i clean it with a cloth.
Does anyone encounter such kind of problem before? I've no more idea on how to clean this strange oil layer anymore! (I don't want to clean it with 99% alcohol)
*some additional detail, there is one lens without oil layer and it's a new Canon Zoom lens(EF mount), and all the lens suffering now are Nikon AI old mf lens
Edited by Hercules Fu, 16 November 2009 - 02:08 PM.