Marks on internal glass of Canon 200-400mm f4L?

[dmaukbobcat]

**EDIT: the last 2 photos are the lens under less harsh light, for context, of how it normally appears**

**2ND EDIT: Added a couple sample shots of its performance in the field**

Recently I purchased a used Canon 200-400mm and it appears in good condition, except for something odd i noticed. This is my first big glass I have owned, so I am not sure if this is just an artifact of manufacturing. 

While cleaning the lens, I noticed that there is a mark inside one of the internal elements that is only visible when a very bright light is shown at an angle almost parallel to the front element. The mark appears circular and like a smudge from polishing, but it is invisible under any other lighting conditions (angle or intensity). Is this just a faint polishing mark from manufacturing, or is this something I should not be seeing? Note that the internal parts of the lens are so free from dust (outside of what is to be expected from manufacturing; dust in the photos is on the surface outside) that I doubt anyone has opened it up to attempt to clean the lens and has, as far as I know, never been serviced by anyone outside of Canon personnel. 

Sample photos; the close in shot of the tern is with the 1.4x teleconverter engaged as the tern flew overhead

 

[jrhoffman75]

Support generally means answering questions and the like. The repair facilities are different. The only absolute answer to your question will only come from calling a repair center.

[shadowsports]

Nice John!  Looking better and better then.  TBD.  There is hope.

[ebiggs1]

 I doubt seriously any of that will harm your photos. And I doubt, seriously, sending it in will give you back a lens that is significantly better. However, I too, like some of the others would want a C&C done as simple maintenance.

My original 600mm L lens, bought some 35 years ago, has never been "cleaned" beyond blowing it off with a Rocket blower.

[Tintype_18]

I have a lens that has what looks like water spots or bubbles. Doesn't affect the photos, though.

Those are great photos! Remember, one good tern deserves another.😏

[ebiggs1]

John

What you are seeing is most likely the lens coating coming off. The lens would work and be just as sharp if the coating was not there at all. It is mostly for lens reflections and aberration.

[dmaukbobcat]

that makes sense, given it is potentially a 10 year old lens (I bought it used, for all I know its one of the first 2013 batch). Thank you! 

[jaewoosong]

one possibility for the "rings" on the inside of the lens element is condensation ring forming on inside of the lens.  as a telephoto lens possibly used in cold weather repeatedly, the temp difference between inside of lens and outside can cause the warm humid air inside the lens to form condensation on the inside lens element when the outer lens element is exposed to cold air.  If the lens was stored vertically, those water droplets could have pooled towards the center of the lens and dried out, leaving some circular mineral stains.  That said, it won't affect the performance of the lense.

[dmaukbobcat]

I apologize for the late reply! The previous owner did shoot with this lens in the arctic....