EF 24-70mm has distractive halo effect around lights at night photos at F2.8

[Tatarin]

Hi, could you please help with such an issue. I observed a distractive halo effect like bright lights around light sourses/street lamps at night photos when shoot at F2.8 with my old but trusty Canon EF24-70L 2.8 (1st generation), after I close diafragm to 3.5 and higher this strange effect dissapers. Is this my lens copy problem or what could cause this? There are no such halos on Canon 17-40 at F4.0 for instance, just with 24-70 on diafragm F2.8-3.5...  I tried to clean lens carefully and shoot without protective filter and nothing changes unfortunately.

Thanks in advance for any suggestions and ideas

[Tatarin]

Just wanted to add that I shoot with Canon 6D. 

[Tatarin]

[Tatarin · Accepted solution]

It sems like I've found the reason - dirty inner lens right on the outter side and when I close the diafragm this part of the lens is beeing covered and impact the image only on the open F2.8, so the lens needs to be shipped to service for cleaning...  

[jrhoffman75 · Accepted solution]

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@Tatarin wrote:

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That looks like it may be fungus. Could be difficult to clean. May have damaged coating. I suggest you keep this lens separated from others because it could spread.

[ebiggs1]

"That looks like it may be fungus."

I agree with JRH. It looks like and probably is fungus. The lens is probably not repairable and certainly not worth the expense to have it repaired if you find someone, unlikely BTW, to clean it. It might make a nice pencil holder.