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12-03-2013, 07:06 PM   #1
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Lens Defects

Would there happen to be an article or page somewhere with pictures of typical lens defects?

Like, some ads say it's "an old lens with light dust inside and light fungus"? What does that look like? And why bother trying to sell it?

Sounds awful! Unless maybe it can be fixed or cleaned or whatever.

12-03-2013, 07:12 PM   #2
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No pictures that I know of. However light dust is common and usually hurts nothing. Fungus is another matter it can be cleaned but unless the lens is rare or valuable is in most cases not worth the effort.
12-03-2013, 07:19 PM   #3
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Well, fungus can usually be killed afaik - but you can't fix the affected portion very easily. So if a lens has very light fungus on the edge, sitting it in the sun for a day straight (or point UV light at it for a few hours) will kill the fungus and prevent it from continuing to spread - and it won't affect image quality at all. On the other hand, it probably looks ugly and no one really would like to have fungus on their lens, so it would command a discount.
12-03-2013, 07:48 PM - 1 Like   #4
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Sometimes fungus can etch the glass and destroy the coatings, so it completely ruins the lens. In a many cases I've been able to successfully clean the fungus from lenses without any damage. I've also had a few that were beyond repair. In one case I have two identical lenses, Pentax M 50mm f2, one I got was in mint condition, one had some pretty serious looking fungus that spread over the entire optical path. After cleaning I tested them and they performed identically and I've long since forgotten which one even had fungus. It wouldn't be worth it to have one of these professionally cleaned, but the whole cleaning process took me about 10 minutes and I wanted to see how well a cleaned one stood up to one that never had fungus.

Another common problem with old stuff is stuck or oily aperture blades, those can be quite tricky to repair. My first experience with that ended up giving me a nice 50mm f1.7 loupe to use when working with small parts. They need to react fast when you flick the lever, if they are sluggish the exposure will be inconsistent.

Stuck or hard to turn focusing rings are common in some lenses, if it is a Russian lens it is almost always just dried out grease, but it can also be a sign the lens has been dropped.

Any of these problems with a zoom you can forget about repairing, they are very complicated and have a lot of parts. Simple prime lenses are easy to work on and can be repaired cheaply by some shops or you can do it yourself if you are brave.

12-04-2013, 05:06 PM   #5
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I'd be more concerned about defects like decentering, or otherwise misalinged elements, which you can't see just by looking at the lens, and may only be visible with careful testing. I did buy a lens once with infinity focus issues, again not something you can see by looking at the lens, but it was trivial to adjust (it was the SMCT 200/4.)

A tiny amount of dust shouldn't hurt anything and would be expected, but other than that, if a lens doesn't look clear when I look through it, I'd pass on it instead of trying to determine the degree of damage. If I was reading an ad and it mentioned fungus, I'd move on, unless it was a very special model that wasn't otherwise available.
12-04-2013, 05:52 PM   #6
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QuoteOriginally posted by tibbitts Quote
I did buy a lens once with infinity focus issues, again not something you can see by looking at the lens, but it was trivial to adjust (it was the SMCT 200/4.)
Many of the longer lenses focus beyond infinity on purpose, as it can change with temperature. Going beyond infinity is better than not reaching it. As long as it reaches infinity and is fairly close to the mark then I leave them alone.

Some are easier than others to adjust. The hardest thing about doing the Pentax M lenses is removing the name ring. Most old third party lenses have the adjustment screws either visible or just under the rubber focus ring.
12-04-2013, 08:32 PM   #7
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QuoteOriginally posted by davids8560 Quote
Would there happen to be an article or page somewhere with pictures of typical lens defects?

Like, some ads say it's "an old lens with light dust inside and light fungus"? What does that look like? And why bother trying to sell it?

Sounds awful! Unless maybe it can be fixed or cleaned or whatever.
It often looks like cobwebs, sometimes like a frosted window. It varies because it's growing like a plant. I thought I had a photo somewhere but can't find it.

An eBay seller might have acquired the lens for almost no cost and is just looking to move it. The bidders will be people already expecting to repair the lens, and they won't return it. I would only bid on something like that if I knew how to take it apart.
12-04-2013, 09:00 PM   #8
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QuoteOriginally posted by elliott Quote
Many of the longer lenses focus beyond infinity on purpose, as it can change with temperature. Going beyond infinity is better than not reaching it. As long as it reaches infinity and is fairly close to the mark then I leave them alone.

Some are easier than others to adjust. The hardest thing about doing the Pentax M lenses is removing the name ring. Most old third party lenses have the adjustment screws either visible or just under the rubber focus ring.
That's a good point, but this one was not even close to infiniity. I suspect the adjustment had slipped over the years.

12-05-2013, 09:43 PM   #9
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You can also have problems with hazing. In my case I believe that it was caused by the evaporation of the blade oils. When I tried taking pictures it was hard to focus. I know my eyesight isn't great but not THAT bad. The quickest way to check is to shine a light through the lens and you'll know right away.
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