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02-02-2011, 02:48 AM   #16
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my take on the marks as they appear to go left to right in uniform makes it look like someone has been in there already and used a cotton bud to clean something in there, possible the start of fungus and they haven't used the correct cleaner so its marked the element. It doesn't look like lens coating seperation due to that zig zaggy pattern (technical eh zig zaggy!) I doubt it'll effect the lens as its too close so will blow out in focusing but I'd keep an eye on it in case it did originally have fungus in as you don't want it coming back and saying hello to your other lenses

02-02-2011, 11:36 AM   #17
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QuoteOriginally posted by GregK8 Quote
BTW, were these marks disclosed to you when you bought the lens? I hope it was discounted appropriately given the damage.

No the lens was sold as clean. The buyer is offering to take back though but if the lens is good, i'd rather keep it
02-02-2011, 03:09 PM   #18
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QuoteOriginally posted by jersey_m Quote
No the lens was sold as clean. The buyer is offering to take back though but if the lens is good, i'd rather keep it
Marks like that on the lens are going to cause some sort of problem - whether it's a loss of contrast or flair when in bight sunlight. Since the seller is offering to take back the lens, I'd say go ahead and return it, then put your $$ into a good, clean lens - you should have no problems finding a good one either here in the Marketplace or on the bay.
02-03-2011, 11:49 AM   #19
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Here's a link showing a strip down

Pentax 50mm f/1.4 strip-down instructions

The 50's I've taken apart are similar. If you have a Home Depot near they have rubber plugs that work well for removing the ring.

R.O.R (Residual oil Remover) is great stuff. I got mine from b&h. When I use ROR, I'll clean with it first and then clean the lens with lens cleaning solution. Sparkles

02-03-2011, 12:53 PM   #20
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WHY is the serial number obscured?

Mickey
02-03-2011, 01:10 PM   #21
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I've understood that a chemical burn to the multicoat, if it does not penetrate to the glass surface, is only an erosion of the metal/mineral. It may be causing a chromatic refraction that physically is only microns deep. The efficiency of filtering the light waves caused by reflections may be less efficient, but the overall lens element is still unchanged.
02-05-2011, 07:52 AM   #22
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QuoteOriginally posted by mickeyobe Quote
WHY is the serial number obscured?

Mickey
I was not sure if would be keeping the lens and it wouldn't have been fair at that point
02-05-2011, 08:26 AM   #23
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I ended up taking the lens to a local camera store and the gentleman there was more than helpful. The lens was taken apart quite easily, The ring with the Pentax 50mm marking was loose and it came out without trouble. The three screws came off next and the front element was off. the marks were not on the front element but between the next group of glass. That needed some effort to twist off but once off the three pieces of glass were easy to remove. A wipe with a new microfiber cloth cleaned whatever the brown marks were. The guy also used a little bit of some mild soap to clean it and the rest of the glasses were cleaned by simply blowing on to it. Eventually the all the pieces looked clean though after assembling we noticed a slight smudge on inside (only visible in bright light). Anyway that was left to me as a take home task ...

The lens looks clean and I think I am keeping it..

Here are some pictures taken in sunlight after cleaning..

Thanks for all your help and suggestions.

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