I was out an about taking photos today and had a couple of lens swaps. When I got back, I gave my kit a check over, blowing most of the dust etc off with a rocket blower.
Now the painful part. On the rear element of my 24-105 there was a spot that would not go away, a bit like a water mark or something. I got out my brand new (unused) microfibre cloth and rubbed it fairly hard from one side to the other... only to notice a large streak across the lens. A bit more gentle rubbing with clean faces of the cloth has got rid of said mark and streak but it has resulted in what looks me rubbing off a film/ coating off the lens! This is only visible in direct sunlight though and not under a normal desktop light.
So, the questions:
1) Has anybody done this before?
2) Is there some sort of film on the rear element of a lens?
2) How do I fix it?
3) Does it matter anyway if I cannot see any trace of it on my photos?
Thanks for any input. I am hoping to hear that I am not as much of a cretin as I now feel.