In a previous I made a living working on optics. A little internal dust is not worth worrying about. A small chip or scratch is not worth worrying about (a dab of flat black paint on a chip is an acceptable treatment). A lot of internal dust is not really worth worrying about, you'd be surprised how much dust it takes to have any effect on images. A fingerprint IS worth worrying about, never allow a fingerprint to remain on a lens. I keep a bottle of ROR and some cotton swabs on hand at all times for just that reason. Dust on the sensor IS worth worrying about - have it cleaned, better yet, get comfortable doing it yourself. Internal fungus is worth worrying about - have it cleaned. Go out and use your lens.
Dear sir (emag)
Thank you so very much for your given facts to me!
I would be quite sure that it is NOT fungus - and there are kind of dust yes but this is like a scratch on the surface more or less what I first tried to gently swab away with a new and clean LensPen and also tried a brand new and clear lenspaper from Kodak but it clearly was INSIDE the and between the two most rear lens-elements.
The good news is that it does not affect the picture as far as I have seen - and also - the fact that I seldom or never use this Canon EF 135mm f/2L stopped down more than about f/5.6 - because one reason to purchase in this type of fast prime is to use it wide open or maybe at f/2.8 - if I need more DOF I usually change to EF 100mm f/2.8L IS USM.
I also checked my EF300mm f/2.8L IS USM that I purchased as brand new and I have been extremely cautious in the process of change of lenses/extenders with this lens and I could not see one single dust particle inside internally in this lens and when I checked my EF 135 f/2L I was quite surprised to find dust in a quality built "L"-lens , that to my understanding maybe should have some kind of dust prevention in the construction/sealings=?
Anyhow I do appreciate your answer as well as all your others answers
to my kind of novice level question - but I am quite relieved by all your answers and no I think I wish not to give my money to Canon for some small fraction of "scratch" on the surface of the coating and some additional dust particles inside this fast lens!
Thank you so very much for your contributions to my first question here on this knowledge-treasure-forum - because of ALL of YOU!
Wishing you all excellent shoots with your also excellent lenses and DSLRs and much fun and joy when enjoying the IQ and results of your photographing!
//All the Best!