I've encountered few issues over these few days. First of all, dusty lens! Just found out that the Voigtlander I just bought have dust on the inside. But actually this is normal for any lenses. I thought it was the dust which caused spots on my shots, but turns out that it is the sensor itself caught dust. Now I must clean the sensor myself.
Then there's the autofocus problem on my Tamron. I suspect it was the PDAF algorithm since CDAF is perfectly fine.
Given the experiences, I come to a conclusion that, like life, there is no perfect lens (and photographic forums around the internet confirm this. Amen) But there's always a good news at the end of it, right ? Right ?! Yep! I just bought the carbon fiber tripod that I need (not want.. I swear :P), and the second GM firmware for my iPad runs without getting a WiFi problem anymore.