Sigma 35mm Art dust? advice please Photo added

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Grumps1974

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Martin
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I was looking at the front element of a Sigma 35mm Art today and I noticed two semi circles of white spots very close to the edge of the lens. These semi circles were identical in the number and spacing of the spots and if I covered one of the outer spots the corresponding inner one would disappear. The outer semi circle was less than 1cm from the lens frame and the inner ones about 1cm further in. I am pretty confident that the inner semi circle was a reflection of the outer circle reflected by the bulbous shape of the front element.

What is not so certain is what the spots in the outer outer circle are. They could be dust. However they form a perfect arc all equidistant from the very outside edge of the front element. They also only go about 1/3 rd round the circumference of the lens. The other 2/3 are completely clear of any spots. It is also noticeable that there are no visible dust bunnies anywhere else in the lens. These spots were visible in a range of light levels so it is highly unlikely they were reflections from the ambient light.

There is no sign that these spots have any affect on IQ or appear anywhere in images.

I have never seen anything like this before. Can anyone throw any light on this matter?
 
I cannot see how it could be as if you rotated the lens the spots rotated with it so they remained stationary relative to the lens. If it was a reflection then the reflection would remain in the same location as you moved the lens. In addition the lens was viewed in different locations with different light sources and the pattern of the spots remained the same.
 
Grumps1974 said:
I cannot see how it could be as if you rotated the lens the spots rotated with it so they remained stationary relative to the lens. If it was a reflection then the reflection would remain in the same location as you moved the lens. In addition the lens was viewed in different locations with different light sources and the pattern of the spots remained the same.
Click to expand...

Strange, find another I guess.
 
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sk66 said:
Sure looks like dust collected at the edge, or maybe spots left by cleaning solution... If the price was right I wouldn't worry about them at all.
Click to expand...

Could be :thumbs:
 
I was inspecting a Sigma Art lens today (18-35mm f/1.8, I think) and I saw something very similar, except in my case the white spots continued in a complete circle. They certainly weren't marks or foreign objects on the glass. They looked to me as if they were part of one of the mostly-black internal components of the lens. If I get a chance tomorrow I'll pull another one off the shelf and look at it, and photograph it if I can. But I don't think it's anything you should be worried about.
 
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