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10-06-2014, 03:01 AM   #1
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Lens Coating Damage ?

I like fiddling around with things to get them to work.

From time to time lenses appear on the market which otherwise would be fine but either the back element or more usually the front has damage to the coating giving a blotchy appearance, I have always thought that using such a lens would have a similar effect to a bad case of sensor dust, am I correct ?

Given that these lenses are usually fairly old and the maker probably long gone the chance of getting this repaired would be uneconomic so I was thinking that you could get quite a nice uncoated lens if the coating was removed entirely and was wondering had any body done this and if so how was the coating removed.

Kind Regards

CD

10-06-2014, 04:43 AM   #2
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Nono, damage in the lens coatings on the front element usually doesn't even show up. Sometimes it can cause things like odd flares and reflections. Basically, inconsistent image quality throughout the frame and loss of contrast. But it won't show up like dust spots, as dark shapes. Only as odd light reflections. On the other hand, if there are marks added to the from element (dust spots), they might show up, but again, very rarely on the front element. There is a bigger chance they show up if they are on the rear element. But there is a big difference between lens coatings missing in some places, and things like dust and bubbles, haze or fungus on the glass.
Removing coatings probably won't help, as you might just damage the lens even more. Keep in mind that older lenses have more primitive lens coatings to begin with, compared to modern lenses. And coatings are different from brand to brand. Having a hole in the coatings might be bad, but removing them even more is worse.

Anyway, just put a tight lens hood on there and it will negate most lens coating problems. You can add a polarizing filter to improve contrast and saturation (but polarizers have other effects as well, and cheap ones can damage image quality)
10-06-2014, 07:52 AM   #3
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^see last post. Coatings that have rubbed off partially will just not provide as as protection from flare, etc. It is more of a problem with wider lenses that are harder to cover well with a hood. Consider that many fine old lenses are hardly coated at all...
10-06-2014, 08:12 AM   #4
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Effects are variable and more often than not the effect on IQ is not noticeable. I would be pretty blase about small marks, a few little blotches, spotting....same with fungus, little bit of fungus here and there doesn't notice. However I have had a couple of lenses with what looked like extensive/near complete removal/degradation of the front element coating - an old 135/2.8 and a sigma 28-70mm zoom. On both lenses the contrast was not just down, but shot! Both were unusable.

10-06-2014, 08:20 AM   #5
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QuoteOriginally posted by vonBaloney Quote
Consider that many fine old lenses are hardly coated at all...
Also consider that many fine old lenses have damaged coatings and they still fetch premium prices.


Steve
10-06-2014, 08:31 AM   #6
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QuoteOriginally posted by Na Horuk Quote
Nono, damage in the lens coatings on the front element usually doesn't even show up. Sometimes it can cause things like odd flares and reflections. Basically, inconsistent image quality throughout the frame and loss of contrast. But it won't show up like dust spots, as dark shapes. Only as odd light reflections. On the other hand, if there are marks added to the from element (dust spots), they might show up, but again, very rarely on the front element. There is a bigger chance they show up if they are on the rear element. But there is a big difference between lens coatings missing in some places, and things like dust and bubbles, haze or fungus on the glass.
Removing coatings probably won't help, as you might just damage the lens even more. Keep in mind that older lenses have more primitive lens coatings to begin with, compared to modern lenses. And coatings are different from brand to brand. Having a hole in the coatings might be bad, but removing them even more is worse.

Anyway, just put a tight lens hood on there and it will negate most lens coating problems. You can add a polarizing filter to improve contrast and saturation (but polarizers have other effects as well, and cheap ones can damage image quality)
Thanks very much for that advice.

If you look in the Lens Discussion Forum in a thread entitled "How much of an issue is fungus" towards the bottom of page 1 is an illustration of a fungal attack on a mirror lens but the spots in the illustration look similar to the ones I was thinking about though of course not on a mirror lens and I don't think they are fungus.

Do they resemble the ones you are referring to ?

CD
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