hi my dad has this 10 yr old canon ef 300mm 1:4 L IS lens. im noob and dunno what is means but it is huge. i noticed when i took inside thru the side where it goes in the cam i can see some marks but its on a layer of glass behind another layer so i cant get to it. is there a way for me to clean it? i cant seem to notice the mark on the pic maybe i didnt know where to look. the cam is a 10 yr old canon eos-1. thanks for the help. and i love this forum already.