Cleaning from fungus: SMC Pentax-M 50 f/1.7

Going on with the lens rescue series, an SMC Pentax-M 50/1.7, one of the best Pentax lenses, is the new patient.

As you can see here, back-lighted by a LED flashlight, a fungus has widely infected the lens.




Since the fungus will reveal to have infected all the elements in the lens, a fully elements removal is required. As usual, before going on, the classic legalese disclaimer:

AS USUAL, I CANNOT BE HELD RESPONSIBLE IF YOU DESTROY YOUR LENS DOING WHAT I EXPLAIN HERE. IT WORKED FOR ME, IT DOESN'T MEAN THAT IT WILL WORK FOR YOU. THIS IS A VALUABLE LENS, THUS CONSIDER THE SERVICES OF A PROFESSIONAL REPAIRMAN BEFORE TRYING TO FIX IT ...

What you will need to proceed:

• A sink cap, to remove the front name ring.
• A spanner wrench (got mine from MFLenses). You can get yours wherever you want, but avoid cheap ones (less than 50€).
• Cold cream. I use Avene's one, but simply because it is really cheap in France. Ask to your beauty-shop (or to your wife) what they have available.
• Zippo fluid or isopropyl alcohol or something similar, to remove the cold cream from the lens.
• Optical cleaning fluid for the final cleaning of the lens.
• A microfiber cloth, to clean the lens.
• A clean workplace and ... some patience ;-) ...

Now, let's start the game ;-) ...

Focus the lens to the infinity first, for easy removal of the rear optical group, then unscrew the front name ring and remove it.




Notice here the two concentric retaining rings with notches for a spanner wrench exposed.




Engage the outer one with the spanner wrench and unscrew the whole front optical group.




Reverse the lens. You will notice here too two concentric retaining rings with notches for a spanner wrench. And here too, engage the outer one with the spanner wrench and unscrew the whole rear optical group.




Let's start with the front cell. Unscrew the retaining ring of the front element.




Notice the inner retaining ring exposed. Engage it with the spanner wrench and remove the second element of the front optical group.




Unscrew the retaining ring of the rearmost element and remove the lens from the rear optical group.




Now you have separated all the five elements of the lens. Using a Q-tip (or the like), spread some cold cream on the lenses.




After about an hour, remove the dried cold cream with either Zippo fluid or isopropyl alcohol (i had the last one available).




Then, clean the lenses with some optical fluid.




Almost done. Rebuild both the front and the rear optical cells and screw them back in the barrel. Last, screw in the front name ring.







Time to enjoy the freshly cleaned SMC Pentax-M 50 f/1.7. A picture of the lens that has been used to take the previous pictures and a portion of the surgical team.




That's all, folks!

Hoping that this will be useful to someone ...