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03-26-2013, 02:42 PM   #1
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Swirly watermark pattern on inner element?

I currently have a Tamron 17-50 f2.8 on its way to me, and I suspect that it will supplant any prime lens within its range that is not faster than it (thus my DA 15 and F 50 1.7 are spared).

This puts my Pentax F 28 f2.8 on the chopping block. Not that I haven't been happy with the lens. The F 28 has the best corner to corner sharpness I have seen out of any lens I have tried, and the 28mm length provides such a good normal field of view. I just simply do not like having lots of money tied up in lenses that won't see much use. So the F 28 will most likely end up on the marketplace soon.

Before I list it though, I want to learn more about a certain quirk it has. When I got it from Ebay it had some weird markings on one of the inner elements. The markings look almost like a light swirly watermark. It is not haze or fungus. I took it to my local camera store and had two of the guys look at it, and they both said it wasn't, and I agree with them because it doesn't look like any haze or fungus I've seen in person or on the internet. It's hard to see it in regular light, and even harder to take a picture of it. only with a lamp and at a certain angle can it be seen, but it's definitely there. They both agreed that it was most likely something related to the coating. Maybe a degradation of the coating due to the age of the lens, or something happened in the factory during assembly.

Regardless, it doesn't affect image quality at all. I simply want to know what it is so I can forward that description to the potential buyer so they are aware before they pull the trigger. Has anyone experienced something similar with one of their lenses before?

03-26-2013, 03:08 PM   #2
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I would say element separation, also hard to describe. It isn't that, because the lens has no glued elements:

03-26-2013, 03:30 PM   #3
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You could say it like it is by including the paragraph from your op.
I have bought many used lenses and some had dust specs, slight marks on elements etc. - doesn't seem to cause problems

What puts me off are swirl marks when somebody has rubbed into the coating.
03-26-2013, 07:34 PM   #4
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QuoteOriginally posted by wombat2go Quote
You could say it like it is by including the paragraph from your op.
I have bought many used lenses and some had dust specs, slight marks on elements etc. - doesn't seem to cause problems

What puts me off are swirl marks when somebody has rubbed into the coating.
What he said...

If you have a good macro setup and oblique lighting, you might also be able to provide a photo of the anomaly.


Steve

04-18-2013, 11:07 PM   #5
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A relevant update.

I came across the following through another thread, and I think it's the answer I was looking for.

Eroded Lens Coatings | Tech ARP

Based on this, I would say I have a case of eroded coatings.

I think it's a mild case, since it does not seem to affect IQ at all, but I'm pretty sure this is it.

Just wanted to post it here so I can find it, but also in case someone searches the forums and comes upon this thread, there is an answer now to the question.
04-18-2013, 11:19 PM   #6
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Could just be that someone took it apart and cleaned the elements, and left a little swirl. When you sell it, just say that it is there and has no effect on IQ...
04-19-2013, 01:56 PM   #7
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QuoteOriginally posted by vonBaloney Quote
Could just be that someone took it apart and cleaned the elements, and left a little swirl. When you sell it, just say that it is there and has no effect on IQ...
I don't think it was opened. The original seller said he didn't, and despite him missing the eroded coatings in the first place, I'm going to believe him. I certainly didn't, as I've opened up an F series AF lens before and totally junked it in the process.

It's fine though, it's really not that bad. Even two of the guys at my camera store had a hard time spotting it. If I hadn't been so paranoid about checking my lenses, I probably would have missed it too.
04-20-2013, 04:45 AM   #8
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Does it look like this :



Then it is probably a production fault, already present when it left the factory.

04-20-2013, 04:49 AM   #9
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QuoteOriginally posted by EarlVonTapia Quote
Swirly watermark pattern on inner element?
It sounds to me like some over zealous cleaning at some point in it's history, if it doesn't affect the IQ, mention and say that, job done.
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