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Archive 2013 · What is this lens defect?

  
 
thormx538
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p.1 #1 · p.1 #1 · What is this lens defect?


Hi all. I purchased a 20mm AI-s from KEH in UG condition, so I knew I would potentially get a lens with some issues. Aside from a well used cosmetic appearance, this is the only defect I noticed on the lens. What is this? It becomes more or less visible depending on the light angle when looking at the lens.This is what it looks like when most visible. It doesn't seem to affect the image quality at all. I don't think it's fungus. Is it the lens coating peeling, or maybe an adhesive between lens groups starting to seperate? My main concern is whether or not this will continue to spread and affect the image quality later on. Any guesses?









Jun 01, 2013 at 12:52 PM
corndog
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p.1 #2 · p.1 #2 · What is this lens defect?


It looks like a coating coming off, but that would be a really dark looking coating...perhaps it was damaged with some gnarly solvent and it now flaking away. It could also be two elements separating, but I'd think you could check that really quick with a finger nail. If it's on the exterior, I'd try to get it all off and see how it shoots.


Jun 01, 2013 at 01:09 PM
Zebrabot
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p.1 #3 · p.1 #3 · What is this lens defect?


Looks like a worn off AR coating on the rear element.

It's not always a big deal, but it is a UG grade lense, so it's not like they lied to you.

It's pretty easy to test if that coating matters all that much, so shoot into some bright lights and see if you get weird reflections, halos or loss of contrast. If not, big deal.




Jun 01, 2013 at 04:11 PM
thormx538
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p.1 #4 · p.1 #4 · What is this lens defect?


Thanks for the replies. It seems like it's on the inside of the rear element. The test pictures I have taken don't indicate any weird reflections/flares, and the images seem the same as my 18-35mm color and contrast wise (20mm seems sharper though)


Jun 01, 2013 at 04:45 PM
mfletch
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p.1 #5 · p.1 #5 · What is this lens defect?


I would venture to rate that UG-

Does it seem to affect images? Usually rear element defects have little impact, but then again I've never seen one look like that.



Jun 01, 2013 at 09:50 PM
M635_Guy
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p.1 #6 · p.1 #6 · What is this lens defect?


Have you shot it on a gray background just to see what shows up?


Jun 01, 2013 at 10:40 PM
ReyGay
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p.1 #7 · p.1 #7 · What is this lens defect?


It looks like someone painted the metal edge of the rear lens elements and somehow a cleaning process smeared the paint all over the lens? Try cleaning the rear lens with pure acetone+pure organic cotton buds and only the glass, not including the metal edges, that might remove that black smear.


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Jun 01, 2013 at 10:46 PM
jlawrence
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p.1 #8 · p.1 #8 · What is this lens defect?


looks like someone sharpie'd it.

vignette was always harder in the prephotoshop days.



Jun 02, 2013 at 11:47 AM
Scott Grant
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p.1 #9 · p.1 #9 · What is this lens defect?


i have a sigma 28-200 that came bundled with a D700 i bought a year or two ago with the same issue. i have no idea of what it is and neither does anyone who has looked at it. It's internal in mine also.

I'm really curious to find out!



Jun 02, 2013 at 11:55 AM
thormx538
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p.1 #10 · p.1 #10 · What is this lens defect?


It's weird, because it disappears depending on the angle of light hitting it. If you hold it right, you don't see it at all. It doesn't seem to be on the outside. The lens is currently with a friend who works at a lens rental company to see if anyone there has seen anything like it before.


Jun 03, 2013 at 07:19 AM
Two23
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p.1 #11 · p.1 #11 · What is this lens defect?


I collect very old lenses (1840s to 1950) and have learned a lot about older lens defects. This could be one of two things I think. It could be the coating beginning to fail, or it could be the cement between two elements beginning to fail. Google "schneideritis" and see what you think. Images should not be affected if you stop down a little.


Kent in SD



Jun 03, 2013 at 08:55 AM
thormx538
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p.1 #12 · p.1 #12 · What is this lens defect?


Got the lens back. General consensus from those at the lens rental company seemed to be that someone used a very harsh cleaner which removed some of the lens coating on the inside face of the rear element. More concerning was a slight but abnormal wobble in the CRC focusing element, so I think I am going to exchange it for a 20mm f3.5 BGN grade lens that KEH has.

Thanks for the opinions and insight!



Jun 04, 2013 at 11:14 AM





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