Max 2.8 said:
Recently I saw some misty thing inside one of my lens, so I sent it in for cleaning. Turn out, the technician told me its fogged and he will need to replace 2 of the elements.
Forgot to ask him, so post the question here, What actually happen when a lens fogged up?
A lens technician (from Yashica) told me that fogging is caused by heat.
Other sources (in other forums) also say that it's caused by heat, and they go further to say that it's due to inferior quality elements (very possibly some kind of plastics used to make the elements, and not glass). Some third party lens makers use plastics to make their elements. They boast of lightness, but not so much of durability or quality. If you think about it, it quite makes sense because plastics degrade over time, especially with heat.
Others, but fewer, say it's inferior quality coating but I doubt this theory. They are also few others who say that it's the lubrication inside the lens barrel which evaporates in the heat, forming a vapour which stains or affects the coating.
MDZ2 is quite correct to say that Sigma tends to have this problem. In other forums, other Sigma owners have also mentioned it.
I have a Yashica lens which fogged up badly but it's cheap and I'm not hurt.
Also, I have a Sigma 400mm APO lens which has fogged up badly. It appears that 1 element inside fogged. The rubbery exterior has also become sticky due to S'pore's heat. It's a useless paperweight in my dry cabinet. It was NEVER used at all because I didn't take it with me to Australia where I now live and work. Needless to say, you can understand how sore I'm with Sigma.
Just out of curiousity, which lens of yours fogged? How much is it costing you to repair?
