Chosen Solution
I asked this back in 2018, but didn’t have the means to get a proper balanced photo of the defect. I know I could edit the 2018 post, but it’s 5 years old and I had bad photos. I have had this lens for quite a few years, as well as a mint 50mm 1:7, and both are “common” as the 50mm was often a kit lens, or a popular add-on at the time it was new. It has no issues and I got a chance to take it out 5 years later; it is freaking good. However, I took this one out with me as well to better inspect it (as well as a backup Sigma with similar range; 28-200 f1:38-5.6 UC) just in case; glad I did, as it was not pretty.
I’m pretty much just about 100% confident this is a crack, which is why I reverted back to the Sigma but was also prepared with a spare Quantaray* which doesn’t go out as far, but is made by Sigma. Is this look usable, or should I dump it in a parts lens lot? *PLEASE DO NOT GIVE ME ANY CRAP about this based on the name like dedicated forums. I know about how quick some people are to rip on someone for having a Quantaray despite most being made by Sigma and not Tiffen since it’s a Ritz special. Mine look like Sigmas.
@nick looks like a crack but looks can be deceiving. I suggest a crack detection with dye penetrant testing (PT). Get some fluorescein and wipe in on the lend. Let is sit for a short time (15-30sec) then simply wipe it off. Now use a UV light and shine it on your lens. If it’s a scratch you can wipe it off, it its a crack the dye will have penetrated into the crack and continue to shine under the UV light.
