Is this a fungus spot on my 24-70 2.8?

[hanhasgotqi]

Greetings to all, 

I recently noticed two spots on the inside of the rear element of my 24-70 2.8L. I thought they were dust particles. However, one of them had a halo sort of thing around it. I have never had fungus in any of my lenses before, so I was wondering if anybody could tell if this is the beginning of a fungus growth. If not, what do y'all think it is? Can dusts cause such a thing on the coating? 

Thanks in advance!

[shadowsports]

Hard to say what that is.  Looks like a foreign body that contained moisture of some sort.  What it is doesn't matter.  Clean it

Then you can decide what to do next.  Start with something damp and super soft.  Lens cleaner, and follow up with canned air.  If it hasn't been sitting forever, it should wipe off.

I would suggest getting into the habit of cleaning your lenses and body after returning home from a shoot.  This way you know they are clean and ready to go the next time you need them.   

[ebiggs1]

"... I was wondering if anybody could tell if this is the beginning of a fungus growth."

Yes someone can!   It is Canon service.  Send your lens in for a C&C today.  It looks like the original 24-70mil so, if that is true, it could very well be fungus and needs to be cleaned ASAP.

[TCampbell]

It's hard to say what that is.  Typically fungus will start to grow on the glass and spreads out across the surface with a vine-like growth structure.  That's just a tiny dot and it doesn't appear to be on the glass - but that doesn't mean it isn't fungus either and if it is... you'd want to catch it soon because once fungus starts to grown on the glass it damages the coatings and sort of "etches" the glass.  It's basically permanent.

I own the same lens and I can tell you there's no spot there on my copy (I am looking at my copy as I write this reply).  So whatever it is... it's not meant to be inside the lens.

Any lens that physically extends or retracts has to allow air to get in and out of the lens.  For the 24-70, there's a gasket that tries to maintain a moderately snug fit and catch dust... but it isn't perfect.  Microscopic bits can get inside the lens.

The only way to have it properly cleaned, is to send it in.  

[Waddizzle]

Send it in.  I would include copies of those photos, including the arrows, in the box with the camera.  You should not need photo prints, but you may want to crop the photos some.  Most any laser printer should do a decent job of it.  Inkjet?  Eh.

[hanhasgotqi]

Thank you for everybody who replied. I'll do as you instructed. Send it in. Hopefully opening the lens will not affect the calibration of the lens itself. It functions perfectly at the moment, focuses well. 

[ebiggs1]

Canon service will go through the lens and make it right.   They are very through.