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07-24-2017, 12:49 AM   #1
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Asahi Pentax-M 50mm f1.4 Lens Haze with Balsam Separation Suspected, Repairing...

Hello all,

I just got my Asahi Pentax-M 50mm f1.4 in very bad condition (at a very cheap price with a vintage Pentax-ME, flash light, zoom lens and 2x tele-converter). I'm trying to clean it up over the weekend and I found that the center group lens unable to clean up after several attempts. This lens contains 7 lens in 6 groups, so that means got 2 lens obviously in 1 of the group and it's balsam glued together. I'm trying to disassembly the center unit until I'm stuck in removing the group lens out from the unit. Photos as below is where I'm currently stuck at. Any one of you know how to remove this group lens and remove the hazy glue and re-glue it back?

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07-24-2017, 05:23 AM   #2
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There is a way.

I 'boil' the cemented group to separate. Then, with acetone, I work the glued surfaces to remove the glue (completely). This takes a little persistence. Then I thoroughly clean to remove dust then apply a small amount of Canadian balsam. Rejoin the groups, press together gently to spread the balsam and then work the elements to remove any bubbles. Thereafter you let the group sit in a dust free environment with some 'guides' to keep the elements aligned.

It takes about 3-4 weeks at room temperature to cement. Remove any excess Canadian balsam then re-blacken the element sides then re-assemble. Should be as new.

Others may suggest different glues. I suggest the balsam as it is easy to rectify any mistakes made.

Enjoy and have fun
07-24-2017, 07:27 AM   #3
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QuoteOriginally posted by Wild Mark Quote
There is a way.

I 'boil' the cemented group to separate. Then, with acetone, I work the glued surfaces to remove the glue (completely). This takes a little persistence. Then I thoroughly clean to remove dust then apply a small amount of Canadian balsam. Rejoin the groups, press together gently to spread the balsam and then work the elements to remove any bubbles. Thereafter you let the group sit in a dust free environment with some 'guides' to keep the elements aligned.

It takes about 3-4 weeks at room temperature to cement. Remove any excess Canadian balsam then re-blacken the element sides then re-assemble. Should be as new.

Others may suggest different glues. I suggest the balsam as it is easy to rectify any mistakes made.

Enjoy and have fun
Thanks for the tips and guidance on the rejoin process.

---------- Post added 07-24-17 at 07:30 AM ----------

QuoteOriginally posted by dcshooter Quote
To remove the center group on this one, you have to pull out the aperture assembly and remove it from the front. This one is cemented with UV cure epoxy rather than Balsam, so the boiling treatment may or may not work. If you choose this method, just be very gentle in heating and cooling, as thermal shock can cause the elements to crack. I personally use methylene chloride-based paint stripper to separate groups, but it is rather nasty to work with, so on a lens this cheap, you might be inclined to avoid it.

Canada Balsam is a good choice if this is your first recement, since it is easy to remove if you screw up. Norland UV cure optical adhesive is (very slightly) optically superior, more stable, and cures in minutes, but if you mess up, it is much more difficult to separate again. The eaiest solution to mechanically align the two elements is to use three prisms to press evenly on the sides until everything is completely aligned.
Thanks for the info on how to remove the center group lens which I'm stuck currently. So I will try to pull out the aperture assembly after removing the 3 worm screws that held on top of the aperture assembly from the center assembly. Thanks for the tips on the lens group repair process as well.
07-24-2017, 09:02 AM   #4
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It looks like there is also fungus on the lens, or am I misinterpreting the photos?

07-24-2017, 11:35 AM   #5
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I hope the coating was not eaten away... that looks very bad.

Its been a long time since I opened my M50/1.4, but the last group should be in a holder that is threaded into the aperture assembly... outer ring hook spanner and sleeve?

You considered boiling the group apart?
Starting with a cold pan and acclimate the group to the water then slowly raise the temp. The groups should sit on a cloth or thick towel to no overheat. The glue may soften at 184 degrees, but you should have a pair of tongs that can grip the elements and exert some torque. Do not lift out of the hot water during this heating process or the temperature difference could shatter the elements. Patience is needed, this may not work the first time and require multiple sessions to get the glue to fail.
07-24-2017, 07:33 PM   #6
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QuoteOriginally posted by leekil Quote
It looks like there is also fungus on the lens, or am I misinterpreting the photos?
Yes, you are right, some of the element got some serious fungus but it is easy to clean up.

---------- Post added 07-24-17 at 07:37 PM ----------

QuoteOriginally posted by MysteryOnion Quote
I hope the coating was not eaten away... that looks very bad.

Its been a long time since I opened my M50/1.4, but the last group should be in a holder that is threaded into the aperture assembly... outer ring hook spanner and sleeve?

You considered boiling the group apart?
Starting with a cold pan and acclimate the group to the water then slowly raise the temp. The groups should sit on a cloth or thick towel to no overheat. The glue may soften at 184 degrees, but you should have a pair of tongs that can grip the elements and exert some torque. Do not lift out of the hot water during this heating process or the temperature difference could shatter the elements. Patience is needed, this may not work the first time and require multiple sessions to get the glue to fail.
Do you know which lens elements with the coating and how to identify those coating and how to tell if the coating is still good?

I'm not sure if I will use boiling water method or will use hot air gun to slowly heat up the group lens to separate them yet. I need to think of how to take out the group lens from underneath the aperture assembly first.
07-26-2017, 05:01 PM   #7
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Light reflecting would be a good first check.
The metallic coat should look continuous no spots.
Also, see how lens cleaner effects it.
Will lines and specks come off?
"...hot air gun..." You keep heat even across all surfaces, if you can't it keep even in all directions, the element may start to fracture if the temps are too extreme.
I've been able to do the boiling technique on a M40/2.8... yes, less glass to cook.
That last group in the tube should be a carrier sleeve...?

07-26-2017, 06:19 PM   #8
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QuoteOriginally posted by MysteryOnion Quote
Light reflecting would be a good first check.
The metallic coat should look continuous no spots.
Also, see how lens cleaner effects it.
Will lines and specks come off?
"...hot air gun..." You keep heat even across all surfaces, if you can't it keep even in all directions, the element may start to fracture if the temps are too extreme.
I've been able to do the boiling technique on a M40/2.8... yes, less glass to cook.
That last group in the tube should be a carrier sleeve...?
OK, thanks for the tips...
07-27-2017, 01:43 AM   #9
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QuoteOriginally posted by dcshooter Quote
You are thinking of the earlier Takumars. On the M, the tube is integrated into the main barrel assembly, and the inner rear group drops in from the front and is secured by a retaining ring which can only be accessed by pulling out the iris. IIRC, this is true of all of the 1.4s from the SMC Takumar with ES coupling up through the SMC-A.

Also, heat gun is a horrible idea due to unevenness of heating and much too high temperatures. Either boil gently, or place he group on top of a 40w incandescent light bulb, and turn on, allowing to heat until the epoxy separates from the glass. Then turn the lamp off and allow to cool to room temperature. Solvent is really the superior solution, but it can be very dangerous if not handled carefully.

SMC coatings are extremely resistant to etching, so there is a good chance that the cloudiness apparent in the cemented group will disappear when the cement is removed, even if the fungus has infiltrated he cement.
Ok, got it. Thanks.
08-08-2017, 08:24 AM - 1 Like   #10
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Some in progress photos for the lens disassembly:
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Last edited by hotfoo36; 08-11-2017 at 10:21 PM.
12-26-2017, 07:57 AM - 5 Likes   #11
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Alright, here are some finished assembly pics of the lens after done the cleaning:
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And below is the photo taken by that lens:
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12-26-2017, 10:19 AM   #12
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Beautiful! Well done.
10-01-2018, 10:16 PM   #13
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I have a M 1.4 with the same problem on the lens group, unfortunately. Thanks a lot for the tips, going to try and follow 🙏

BTW, what else can be used as cement besides Canadian balsam?
10-02-2018, 05:53 PM - 1 Like   #14
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QuoteOriginally posted by hcarvalhoalves Quote
I have a M 1.4 with the same problem on the lens group, unfortunately. Thanks a lot for the tips, going to try and follow 🙏

BTW, what else can be used as cement besides Canadian balsam?
Besides Canadian balsam, you can use epoxy or UV curable glass cement but once you use it, it's harder for you to separate them in future if compare to Canadian balsam.
10-02-2018, 06:45 PM - 1 Like   #15
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QuoteOriginally posted by hotfoo36 Quote
Besides Canadian balsam, you can use epoxy or UV curable glass cement but once you use it, it's harder for you to separate them in future if compare to Canadian balsam.
I tried UV curable glass cement. It ruined my lens. I don't suggest trying it.

It might work OK after you've done a few lenses, but I can not image anyone making it work perfectly the first time.
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