A few months ago I bought a Sigma 18-200mm OS lens from a store in Taiwan, and things have been going great. However, I noticed that there are some spots when I shoot in smaller apertures. These are not dust spots on the sensor, but I believe spots on the internal lens. You can see them through the viewfinder. Despite having a UV filter to cover the lens cover, I suspect dust to have creeped in from the side. The good news was that in Taiwan you get 3 years of warranty with Sigma lenses, but unfortunately, I'm not in Taiwan anymore.
In Taiwan, there is a street dedicated to just selling cameras and lenses, it's an amazing place.
I also got a Sigma 150-500mm OS HSM lens from another seller. However, I noticed at 500mm it has big sharpness issues, and ghosting around the image. I also noticed some dust getting into the lens, despite using a UV filter, as with my 18-200mm. Is this a defect or is it normal with this lens?
I used to have a non-OS version of the 18-200mm. I used it with my old Rebel XTi/400D, but both fell in the water and it almost got wrecked!
The dust and dried water in the lens was so noticable, there were sploches all over the lens. I was still forced to use it until I could get a new camera and lens. Even though some focus points don't light up anymore, it still worked, but I gave it to my dad along with the lens which was cleaned, as I got an XSi and an OS version of the same lens.
From what I heard, Sigma has good service, but some have complained about their quality control.
What should I do about these problems I'm having, since I'm not in Taiwan anymore?