While at a thrift shop, I came across an old Olympus PEN FT with a 20mm f3.5 lens attached. Although I had hopes of shooting film on using this camera and lens, it turns out that not only was my desire to shoot on film minimal, but the attached lens had some fungus between some of the elements.

Given that the lens itself isn't very expensive and that I had a not-insignificant desire to see how well this lens performs when paired with a modern Olympus E-P1, I decided to take a small risk and take the lens apart.

This lens is not terribly complicated, but with any operation like this, I recommend taking detailed notes.

Warning: I really have no idea what I'm doing here -- although this turns out successfully for me, you should follow these instructions at your own risk.  Please do not do this with any lens you consider valuable -- it is quite easy for you to permanently damage your lens.

Step 1: Disassembling From the Back of the Lens

If you look at the back of your lens, you'll find two screws; unscrewing them will allow you to remove the rear panel of the lens. 

Step 2: Removing the Focusing Ring

Unscrewing the three highlighted screws will allow you to remove the focusing ring.

Step 3: Removing the Rear Lens Element

For accomplishing this, I had to be a little creative -- although there is a proper tool for this, I didn't have one at my disposal.  Be very careful if you follow this step!  Also, there is no need to follow this step if you do not see fungus behind the rear lens element.

First, find a pair of pliers and wrap the nose of the pliers with electrical tape to prevent the pliers from damaging or scraping the lens.

Then, grip the plastic piece holding the lens.  Turn counter-clockwise to remove the plastic holder.

Finally, find either a suction cup or something sticky to use for pulling the lens out from its recess.

Step 4: Starting From the Front

After removing the rear lens element, I realized I was at a dead end and started disassembling from the front.

Step 5: Removing the Filter Ring

Using a very small screwdriver, find the notch in the groove between the filter ring and plastic area surrounding the lens.  Gently push it counter-clockwise to unscrew the filter ring.

Step 6: Removing the Aperture Selection Ring

Lift the aperture selection ring off of the lens.  Be careful -- the aperture selection ring is composed of two separate parts having a marble in the middle (what you feel when you click the aperture up or down to the next stop).

Try to keep track of the orientation of this piece as your remove it; you'll need to put it in in the same position when re-assembling the lens.

Step 7: Removing the Front Lens Assembly

Find the notch on the edge of the lens assembly.  Using a small screwdriver to apply counter-clockwise force, unscrew the lens assembly from the base of the lens.

Step 8: Separating the Front Lens Assembly

Still not quite to where the fungus was, I needed to disassemble the lens further.

Using the elecritcal-tape enhanced pliers from step 2, grab the back of the front lens assembly and unscrew it from the front lens assembly by turning counter-clockwise.

Step 9: Now, You Have the Front and Rear Parts of the Lens Assembly

After unscrewing, you'll end up with two (sets of?) lenses.  It isn't entirely clear to me whether you can further disassemble this, but the fungus I was looking for was found on the front part of this lens assembly.

Step 10: Cleaning the Lens and Re-blacking

I used some lens cleaner to remove the fungus from the lens. This lens cleaner also appeared to remove some of the blacking around the edge of the lens.  I used a black permanent marker to re-fill those parts.

Step 11: After Re-assembling

After re-assembling the lens, it is as good as new!
Very impressed. You work cleanly and neatly. Well organized. Thank you for your lessons.
Good work, thanks for sharing.

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