I'm going to take a guess here. Did you put a filter on the lens?

Every dealer tells that lah. Cheap filter degrades sharpness. Actual good clear ones actually cost quite a bit though very subjective so don't go buy any expensive filters just cause you're rich.

Besides, dust doesn't get in through the front lens lah where the filter attach. It gets through the holes on the lens body which you cannot avoid so don't bother. You WILL see dust after some use but it won't degrade image quality.

Take off the filter and shoot again and see if any difference.

This post has been edited by DaddyO: Apr 8 2016, 10:51 PM

"Weather proof" not "dust proof". Dust mostly get into the lens due to the vacuum in the lens when you zoom in or out. Primes too cause they still need to move the lens for focusing but less prone.

This post has been edited by DaddyO: Apr 8 2016, 11:07 PM

There are bunch of internet articles on that already with test and everything. If you want to find out, you can introduce some particles like a strand of hair on your filter and take a shot at wide aperture. Then slowly narrow down the aperture and re-shoot.

After some reading, you are right. It's a rather odd definition considering I still see people having all sorts of foreign stuff inside their lens despite "weather seal". Well, I'm not familiar with construction of weather sealed lens anyway.