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07-28-2009, 10:04 AM   #1
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Taking apart an SMC M 135/3.5

Hi,

I have recently bought an SMC M 135/3.5 with minor fungus behind the front element with a view to cleaning it up. I have previously removed, cleaned and replaced the front element on a SMC M 50/1.4, following this guide:

Pentax 50mm f/1.4 strip-down instructions

However, the 135 has proved more of a challenge as the front element doesn't appear to be mounted in the same way as on the 50mm lens. I can remove the front ring (the one with the serial number and 'PENTAX SMC written on) with the aid of a rubber cup, but the mount for the front element doesn't have notches for a lens spanner as on the 50mm lens.

I've trawled several forums and Google, but haven't found anything relevant to this specific lens. It wasn't expensive and I have another (mint) copy, so I'm not too worried about damaging it, but would be very grateful if anybody has any useful advice or could point me in the direction of a useful guide or diagram.

Thanks.

07-28-2009, 10:32 AM   #2
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An interesting challenge!

If you peel off the rubber focus grip, you'll expose six holes underneath it. Focus to infinity and slide the hood forward a bit. Now three screws are visible in three of the holes. I think when they're removed, the front barrel will come off somehow. My lens's screws are super tight so I gave up there. If you shine a flashlight into the front element, you can see spanner slots on the other side for separating the three elements.
07-29-2009, 10:36 AM   #3
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Got them, thanks. If it's any consolation, the screws on mine are really tight too.
01-28-2010, 11:24 PM   #4
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Hello gjw297

What were the results of this repair? Is the lens still working properly? I'm curious because I have this lens, and an M 200 F4; both of which I plan to disassemble for dust and fungus removal. How difficult is it to separate the element groups if necessary? I have heard that acetone will dissolve the bonding agent. Do you think the acetone will damage the SMC coatings?

Thanks in advance for your reply,
Shimbabwe

QuoteOriginally posted by gjw297 Quote
Got them, thanks. If it's any consolation, the screws on mine are really tight too.


01-29-2010, 10:53 AM   #5
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QuoteOriginally posted by Shimbabwe Quote
What were the results of this repair? Is the lens still working properly? I'm curious because I have this lens, and an M 200 F4; both of which I plan to disassemble for dust and fungus removal. How difficult is it to separate the element groups if necessary? I have heard that acetone will dissolve the bonding agent. Do you think the acetone will damage the SMC coatings?

Thanks in advance for your reply,
Shimbabwe
I am pretty sure the M200/4 is one of the lenses that unscrews in the middle. Slide the hood out, focus to the minimum distance, and grab the barrel between the hood and focus ring. It shouldn't take herculean strength to unscrew it. You'll end up with the elements in front of the aperture blades in one hand and the rest of the lens in the other.

Acetone will dissolve the lacquer that sometimes locks the retaining rings. A few drops and a minute or so is enough. You can see lacquer if it's there. It doesn't damage coatings, but it does melt plastic. I use it sparingly because I'm never sure exactly what dissolves the glue that cements elements together. A lens spanner will help with the individual elements.
01-29-2010, 06:05 PM   #6
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Thanks for the info, Dave. I'll have a go at the 135 first, since I have two more 135's I can use, if I muck up the infinity focus or something. The M200 is my only option for covering that focal length, besides a big and heavy Sears 60-300 zoom.

QuoteOriginally posted by Just1MoreDave Quote
I am pretty sure the M200/4 is one of the lenses that unscrews in the middle. Slide the hood out, focus to the minimum distance, and grab the barrel between the hood and focus ring. It shouldn't take herculean strength to unscrew it. You'll end up with the elements in front of the aperture blades in one hand and the rest of the lens in the other.

Acetone will dissolve the lacquer that sometimes locks the retaining rings. A few drops and a minute or so is enough. You can see lacquer if it's there. It doesn't damage coatings, but it does melt plastic. I use it sparingly because I'm never sure exactly what dissolves the glue that cements elements together. A lens spanner will help with the individual elements.
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