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01-25-2010, 09:27 PM   #1
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Strange blotch on lens

I may have asked about this before, but only now do I have good photos of it. I have an M50/1.7 that has a strange blotch inside the optics and what appears to be a fair amount of dust. Can anyone identify what the blotch would be? It's not spidery like the mold I've heard of, and it doesn't seem to affect photos at all. How much do you think this impacts the value of the lens (I'm looking to sell it)?

Edit: the blotch is only this visible at an angle, though slightly visible straight on (it is very faintly visible if I look straight through the lens at a bright white).


Last edited by jzietman; 12-16-2010 at 09:02 PM.
01-26-2010, 05:10 AM   #2
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To my opinion this can be caused by one of two things . 1) Calcium and other salts after being immerged in water and dried afterwards . In this case I suppose it can be easily cleaned by a qualified repair workshop , but I don't know if selling it you'll get back the money spent .
2)A pair of elements that originally were cemented togeather are now separated . This needs
a much more costing repair and I think you'd better buy another one .
01-26-2010, 06:03 AM   #3
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I don't think this shows separation. Separation is usually not accompanied by this many single small spots. I guess, the first guess by pniauris is going in the right direction. It could also just be cleaning marks, left over by too violent rubbing (damaging the coating) or an inappropriate cleaning agent.

You could give it a try with wiping with a good lens cleaning fluid. I always prefer the Hama ProPhoto cleaning tissues, but simply pure isopropyl alcohol should also do the job. Use Pec Pads or similar high quality single use pads for the cleaning to avoid spreading even more residue around.

Ben
01-26-2010, 03:58 PM   #4
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I am certainly no expert, I had a similar looking blotch on my lense, I assumed it was residue from a fingerprint. I could not get it off. Then I used a tiny amount of isopropyl alcohol (rubbing) and with a q-tip I gently wiped it being careful not to let the alcohol run to the sides of the lense. In my case it worked, but mine was certainly on the outside of the lense.

01-26-2010, 07:21 PM   #5
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Hmm, the isopropyl didn't do anything. I think the blotch is inside the glass...
01-26-2010, 08:19 PM   #6
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As noted above...most likely separation or severe water spotting from being immersed.

Steve
01-26-2010, 09:21 PM   #7
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QuoteOriginally posted by jzietman Quote
...How much do you think this impacts the value of the lens (I'm looking to sell it)?
My honest appraisal: This lens is too common. Anyone who sees a photo like that should just move on to the next M50/1.7. Its value now is for parts, with the optimistic possibility that the problem can be fixed by disassembly and cleaning. Someone looking for parts has another lens already, so they aren't going to shell out a lot for this one. An optimistic fixer like myself has to be thinking about the lens's ultimate value, the possibility of a fatal issue like damaged coatings, etc. I'm thinking $5 + $5 shipping. If we were talking about a 400/2.8, there would be a lot of optimistic fixer competition, and an eBay auction might bring in 60% of an unbroken copy.

It won't surprise anyone that my conclusion is to open it up yourself. If it's fixable, it's going to be an easy fix, and as long as you get it back together right, you can sell it for the going price. Right now it's a Schrodinger's lens, an unknown issue.
01-26-2010, 09:27 PM   #8
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QuoteOriginally posted by Just1MoreDave Quote
My honest appraisal: This lens is too common. Anyone who sees a photo like that should just move on to the next M50/1.7. Its value now is for parts, with the optimistic possibility that the problem can be fixed by disassembly and cleaning. Someone looking for parts has another lens already, so they aren't going to shell out a lot for this one. An optimistic fixer like myself has to be thinking about the lens's ultimate value, the possibility of a fatal issue like damaged coatings, etc. I'm thinking $5 + $5 shipping. If we were talking about a 400/2.8, there would be a lot of optimistic fixer competition, and an eBay auction might bring in 60% of an unbroken copy.

It won't surprise anyone that my conclusion is to open it up yourself. If it's fixable, it's going to be an easy fix, and as long as you get it back together right, you can sell it for the going price. Right now it's a Schrodinger's lens, an unknown issue.
Any guides on the internet I could follow as I make the attempt?

01-26-2010, 09:51 PM   #9
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QuoteOriginally posted by jzietman Quote
Any guides on the internet I could follow as I make the attempt?
I can do a quick one right now. Some tools:



Use the rubber thing to press into the "name" trim ring on the lens and unscrew it via the filter threads. When you get that off, you'll see this:



The screws marked with red arrows hold on the filter ring, but you probably don't need to remove that. The 2 small rectangular slots just inside the filter ring are what you want. I use the middle or right-hand tool as a lens spanner to fit in those slots and unscrew the front lens group. You'll end up with something like this:



The filter ring was removed in that shot. Now try and figure out what surface had the problem. If it's in the front group, it's not element separation. Only the rear group has glued elements. The groups are held together with smaller concentric rings and slots for a lens spanner, if the problem is within a group.

If you remove the 5 screws for the mount, you'll see this:



You can probably dispense with the lens spanner and get a good enough grip to unscrew the rear group.
01-26-2010, 10:08 PM   #10
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Love your spanners Dave!

Steve

(What works, works...)
01-26-2010, 10:16 PM   #11
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Any tips on what I could use for a "rubber thing?" I'm having trouble getting a good grip with what's i've got. Of course, I'm also trying to do this without a clamp...
01-26-2010, 10:30 PM   #12
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QuoteOriginally posted by stevebrot Quote
Love your spanners Dave!

Steve

(What works, works...)
You would think that someday, I would break down and buy the real thing.

QuoteOriginally posted by jzietman Quote
Any tips on what I could use for a "rubber thing?" I'm having trouble getting a good grip with what's i've got. Of course, I'm also trying to do this without a clamp...
Mne is leftover from a plumbing fitting. A rubber cover for a crutch tip or chair leg might work. Some carving may be required to avoid touching the front element. The real tool does not look a whole lot different from an improvised version.
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