About a month after I got my first DSLR, I left a screw-in filter type "macro" magnifier attached to the front of my lens. The next time I came to use it, I couldn't for the life of me, work out why my pictures were coming out all blurred and the lens wasn't focusing properly. "Typical" I thought, having only bought the lens off eBay a few weeks prior.
Cursing my luck, I decided to contact the vendor. While the computer was booting up, I sat at my desk and began to inspect the lens, looking for anything out of the obvious. It was then that I spotted the magnifying filter stacked on top of the UV filter