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12-01-2014, 03:48 AM   #1
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Disassemble front element of zoom lens SMC DA 50-200mm WR

Hello, I've just noticed some mold starting to grow on the back of the front lens of my SMC DA 50-200mm WR. It's still at the beginning, it's growing from 2 different sides but just at the outer circumference of the lens, so I would like to stop it as soon as possible. I'm currently in Indonesia, that means high humidity, rainy season, no sun for uv radiations. I will soon buy more silica gel, but in the meanwhile I would like to clean this lens. I don't know if there are any reliable center here that could do the work, and if it would be worth the money. So I would like to try myself. I actually already unscrewed the front element, using a rubber diy tool, but now I'm blocked. As visible in the photo I took out the front element (mold not visible in the photo, but present) and it looks like the ring where are the writing might be unscrewed. I've tried the same system I used to unscrew the element but it's not working. Before pushing harder, I would like to make sure that that's the proper way to disassemble it? I have to unscrew the ring with the writing and below there might be some screw? Rotation to unscrew the ring is still counter clockwise?
I checked the disassembly database, but it's not helping, since it's showing the disassembly starting from the back.
Some may suggest to buy a clean second hand lens instead, but that's not my plan for now, and my budget is really limited.

Sorry for the quality of the photo attached, but it's just to give an idea. thanks for the help! Davide

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12-01-2014, 05:49 AM   #2
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Trim rings like that usually just screw off in the normal direction. Find a bottle cap, rubber drain stopper or furniture leg pad of the correct diameter to fit the ring and twist it off. You should cover the edge of the bottle cap with electrical tape or something similar to give it some grip.

Underneath there is probably a retaining ring with slots or holes for a lens spanner. You can improvise something with scissors, calipers or compass/divider. It should also unscrew in the normal direction.

It is possible that group cannot be disassembled any further. Minolta started doing this in the mid 80s on some of their lenses. You can find a youtube video of somebody trying to (unsuccessfully) clean fungus out of a sealed group from a Minolta lens.
12-01-2014, 09:16 AM - 1 Like   #3
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The "name" ring is glued on. I used a plastic screwdriver to pry it up. Anything plastic will work - sharpen the edge a little with sandpaper or a knife. A photo of my lens after removing that nameplate.


IMGT9405
by just1moredave, on Flickr

The screws in my photo hold the elements into a piece with external threads. The pieces are separated in this photo:


IMGT9408
by just1moredave, on Flickr

I don't know if that front group can be disassembled further. I didn't have to. I was removing one of those gold-colored washers to get my lens to focus to infinity.
12-01-2014, 10:43 AM   #4
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Thank you for the tip! Just for confirmation: I see in the last photo that the lens in the image is a Sigma, so a different model than mine. Is it still going to be for sure the same system with glue also in mine, or it's just one of the possibilities? Thank you!

12-01-2014, 11:21 AM - 1 Like   #5
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QuoteOriginally posted by phidias81 Quote
I see in the last photo that the lens in the image is a Sigma, so a different model than mine.
I think he was just using the Sigma hood to hold the lens. The lens pictured is definitely a Pentax. Dave is one of the resident experts on lens repair.

Steve
12-01-2014, 01:48 PM - 1 Like   #6
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I'll call it "willing to take his lenses apart rather than admit a purchasing mistake".

The photo does have a Sigma lens hood propping the lens up, just the handiest prop within reach. My serial number is 4044793. It's the same lens name as yours, DA 1:4-5.6 50-200mm ED WR. I don't know if there are different construction versions of this model.
12-01-2014, 07:18 PM   #7
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Ok perfect! I'm going to try to remove the sticker with your method. And what about the space in between the 2 lenses? Is that an air tight area with a "controlled climate", in the sense that the humidity should be kept low, or is it ok to open it and close it in any environment? Sorry for the basic question, but it's my first time dismantling a lens.

---------- Post added 12-02-14 at 11:55 AM ----------

EDIT: I managed to remove the sticker after sharpening a plastic piece with sandpaper. Now I have access to the screws, that I have verified I can unscrew with a screwdriver of my gf glasses. I'm still not going further because I'm wondering if it would be better to do the operation somewhere else where there is air conditioning and a lower relative humidity, or if that doesn't count
12-02-2014, 10:04 PM   #8
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I unscrewed the 4 little screw below the sticker, and I removed the ring visible in the second photo of Just1MoreDave. The ring is actually coming from the back, and its only function looks to be the one of having the screw thread. So I'm at the same level of disassemble as the last picture and I can't go further. It looks like the plastic is just one piece, I can't see or imagine any possible way of opening it further. There are 2 opposite grooves on the same plastic rings as the screw holes, but it doesn't really look like there is any possibility to unscrew something, it's just one piece. The only clue I see is a screw thread in the interior of the front element, below the front lens (slightly visible in the last picture), but I don't know if it's there to refract light or if it's a construction thing or whatever. Anybody managed to go further than this point, or has any hint? Or they are just cemented and it's no way to disassemble them?
If so, then I guess my only option is to use UV lamp to kill the mold, that should remain there, withouut affecting too much the quality of the photo. How can I understand when the mold is dead?

01-12-2017, 12:11 PM   #9
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QuoteOriginally posted by phidias81 Quote
Hello, I've just noticed some mold starting to grow on the back of the front lens of my SMC DA 50-200mm WR. It's still at the beginning, it's growing from 2 different sides but just at the outer circumference of the lens, so I would like to stop it as soon as possible. I'm currently in Indonesia, that means high humidity, rainy season, no sun for uv radiations. I will soon buy more silica gel, but in the meanwhile I would like to clean this lens. I don't know if there are any reliable center here that could do the work, and if it would be worth the money. So I would like to try myself. I actually already unscrewed the front element, using a rubber diy tool, but now I'm blocked. As visible in the photo I took out the front element (mold not visible in the photo, but present) and it looks like the ring where are the writing might be unscrewed. I've tried the same system I used to unscrew the element but it's not working. Before pushing harder, I would like to make sure that that's the proper way to disassemble it? I have to unscrew the ring with the writing and below there might be some screw? Rotation to unscrew the ring is still counter clockwise?
I checked the disassembly database, but it's not helping, since it's showing the disassembly starting from the back.
Some may suggest to buy a clean second hand lens instead, but that's not my plan for now, and my budget is really limited.

Sorry for the quality of the photo attached, but it's just to give an idea. thanks for the help! Davide
I know it has been quite a while since you inicially posted, but anyway, I am currently facing the exact same problem and through some Googling encountered your post here. I have also taken out the front element of my 50-200mm (not a WR) and there seems to be no way (at least not a responsable way) to separate the two optic elements of the front. Maybe, in a moment of anger, I will forcefully do it, but only once the lense becomes inadequate to take pictures with.
I have exposed the front element to strong sunlight and as a result it created a huge damp spot right in the middle between the two optic pieces. Since the element is completely sealed off, you can only come to the conclusion that the moisture (which obviously also contained the incicial funghi organisms) has been left there on assembly in the factories.

Any news that I might have in future; I will surely post.

Cheers,

Johannes
01-12-2017, 04:10 PM   #10
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The optical diagram here doesn't show any cemented elements in that front group. Since it has 3 individual elements and no visible mechanical fasteners, I think they are glued in with something. My best guess is to try the favorite solvent of dcshooter - methyl ethyl ketone, MEK. Maybe a test drop of solvent on the plastic carrier to see if the plastic melts, which is bad. Then if it doesn't melt the plastic, solvent around the rim to see if the element loosens.

Last edited by Just1MoreDave; 01-12-2017 at 04:15 PM.
01-12-2017, 04:37 PM   #11
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QuoteOriginally posted by Just1MoreDave Quote
The optical diagram here doesn't show any cemented elements in that front group. Since it has 3 individual elements and no visible mechanical fasteners, I think they are glued in with something. My best guess is to try the favorite solvent of dcshooter - methyl ethyl ketone, MEK. Maybe a test drop of solvent on the plastic carrier to see if the plastic melts, which is bad. Then if it doesn't melt the plastic, solvent around the rim to see if the element loosens.
Yeah, I too believe the plastic parts are glued together, but the parts fit so extremely tight that it is probably very hard to get whatever solvent between them to at least start acting. However, your approach seems really to be the only possible way...

Better would have been a more careful assembly in order to avoid the growth of fungus. Although I live in an extremely humid tropical region, the only fungus growing within my lenses is fungus between those inaccessible elements.

Anyway; thank you dearly for your reaction!!!

Cheers
01-12-2017, 04:48 PM   #12
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QuoteOriginally posted by phidias81 Quote
I actually already unscrewed the front element, using a rubber diy tool
Brilliant ! Thanks for that - now I've been able to get rid of an annoying bit of fluff which somehow got behind the front group. It made no difference whatever to IQ but had been bugging me for months ...
01-12-2017, 05:21 PM   #13
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QuoteOriginally posted by kh1234567890 Quote
Brilliant ! Thanks for that - now I've been able to get rid of an annoying bit of fluff which somehow got behind the front group. It made no difference whatever to IQ but had been bugging me for months ...
Great, I am happy to learn that my frustrated efforts at least caused some satisfaction! Good luck to you!
04-15-2017, 08:19 AM   #14
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Use a friction wrench on the next element. Also usually you need to tap it out lightly and carefully. But that second group of elemts will come out with a friction wrench.
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