Can someone identify this lens affliction? Spot with a ring

[justtorchit]

I recently got (what I believe to be) a very reasonable price on a Tokina MF 300mm f/2.8. In my shooting, it is definitely a great lens for the money. Although the exterior shows use, the optics look very good. There is only one ailment that I can see, and since it is so far off the center of the glass, I can't imagine it's affecting image quality. It reminds me of a crumb on a napkin where the moisture or oil creates an outer ring around the crumb. I was wondering if this might be some particulate around which the oil is being drawn out on the optic. If someone could help I would appreciate it!

[luisalegria]

Could be a bit of element separation, also could be an area of damaged coating around a bit of acidic debris maybe. It could be many other things also no doubt. Is it on the surface of the front element or behind it ?

[justtorchit]

best I can see, it is one of the inner elements. Definitely not the front, 2nd or 3rd in perhaps.

[themoleman342]

Might be that the retaining ring was tightened way beyond necessary and a natural weakness in the thinnest part of the glass (edge) cracked in this fashion.

[egidio]

this is probably something that you don't need to worry about

[Bruce]

it looks as a better shot of this is possible, maybe a good macro set-up. From its looks I wouldnt rule out fungus... I see feathering?

[Pancolart]

I think it's fungus too. Put it under UV lamp for 15min few times.

[my_photography]

[martinsmith99]

Not remove but stop the growth.

I don't think it is fungus. It looks like the lens has been exposed to pressure at this point or a flaw in the glass. It may have been dropped or the retaining ring over tightened.

[justtorchit]

I don't think I can obtain a better image because the mark is several elements back and the optics in front of this element, like a fish tank, skew the mark as I move about (also it is so near the edge, the optics are rather distorted here). This is the best angle I was able to find and even still it is slightly out of focus. One more observation, as I rotate the lens in my hand, I can see the coating sort of brandish a distinctly different bluish right on this spot, rather than the green of the rest of the element on which this mark sits. No idea if that means anything but thought it worth noting.

Either way. I wouldn't be surprised if it is a pressure mark. Looking closer in the lens, I see a couple screws on one of the inner tubes which appear to be scuffed indicating someone has opened this lens.





My guess is you all are right who believe the ring may have been tightened too far. The lens hasn't shown any focusing issues or optical degradation so as I said, I am not worried about it so much as curious what this mark is. I have seen it in other lenses as well.

It's a great piece of glass and I am getting some great results! here are just a couple (with the color amped up obviously, I love saturated colors):

[gaeger]

Fantastic images, so maybe the spot is nothing to worry about!

[dnas]