Canon Serenar 50mm f/1.9 Lens Clean, Lubricate, Adjust (CLA)

Here’s a rather thorough walk-through of the disassembly, cleaning, and reassembly of a circa 1950 Canon Serenar 50mm f/1.9 lens. You can read about its history in another post.

Please read my general instructions before attempting a CLA.

(follow the images left to right, top to bottom)

Before disassembly.

Remove the three screws holding the depth of field indicator ring/helicoid/m39 thread mount.

Clean the helicoid well. Apply a thin layer of white lithium grease.

Remove this retaining screw. It’s important to use the correct size screwdriver blade. It should be almost the same width as the slot and thick enough to not have play. Using too large or too small a blade can result in damaging the head, sometimes making it unremoveable.

Remove the retaining screw.

Remove the collapsing ring stop by unscrewing it.

Remove the collapsing ring stop by unscrewing it.

Remove this set screw.

remove the set screw.

The set screw is removed.

Unscrew the front lens section.

Here are the loose paint chips.

Clean off the old black paint from around the edge of the lens. Acetone will remove paint.

I had this can of flat black paint lying around.

Apply flat black paint to the edge of the lens.

A fresh coat of flat black paint.

Remove this screw on the aperture indicator ring.

Removing the screw on the aperture indicator ring.

The aperture indicator ring screw. Notice that it has a pin that mates with the brass aperture ring.

Here you can see the brass aperture ring pin hole.

Slide the brass aperture ring down.

The brass aperture ring is slid down. It can be removed by carefully spreading it, or after the aperture and focusing sections are separated.

Clean the brass ring.

Remove this black retaining ring and the lens section beneath it. This will free up the aperture housing.

A look at the loose aperture blades.

The aperture housing top sitting next to the focusing section.

Cleaning the aperture housing top.

Remove the aperture blades. Notice the top pins are offset, while the bottom pins are centered.

The aperture blades dry after being cleaned.

Remove the set screw on the collapsing ring.

Removing the set screw.

Use a spanner tool on this inner retaining ring. This will free up the collapsing ring and separate the aperture and focusing sections.

Remove the inner retaining ring.

Now the collapsing ring can be separated from the outer focusing ring.

Notice the spring-loaded guide pin inside the ring.

Remove the guide pin and spring.

The hole for the guide pin and spring.

Unscrew the knurled housing from the focus indicator ring.

Removing the knurled ring.

With the knurled ring removed.

Remove the brass focus ring.

Remove the brass focus ring.

With the brass focus ring removed.

There’s no need to remove this screw. It only acts as a stop for the brass focus ring.

Use a spanner tool with fine points to grab the tiny indents on the small brass retaining ring. Note that the small brass ring is partially held in by crimps along its edge.

Here’s a close up of the small brass retaining ring.

Once loose, use a small flat blade screwdriver to unscrew the small brass retaining ring.

Separate the two parts.

Here you can see one of the crimps used to hold the small brass retaining ring in place. Use a utility knife to clean up and re-thread the threads if they create too much friction on the small brass retaining ring.

My cleaning solutions: naptha, rubbing alcohol, white lithium grease, acetone, and teflon/ceramic lubricant.

Clean the ring using acetone.

Place the q-tip in a plastic bag and spray it with teflon/ceramic lubricant.

Apply the teflon/ceramic lubricant with the q-tip. A small amount of white lithium grease can be used instead.

Remove and clean the aperture indicator ring.

Remove the brass washer so it doesn’t get lost.

Unscrew the lens element to clean the other sides of the lens elements.

A look at all of the parts exploded.

A look at all of the parts exploded.

Re-seat the aperture blades. This can be a very frustrating experience. Note that the pins on the ends are not the same. One end is offset, while the other is centered. The centered pins go into the bottom of the aperture housing.

Notice the slot for the aperture indicator ring set screw pin.

The aperture housing is seated.

Reassemble and carefully tighten the set screw. The threads are very small and delicate. It doesn’t need to be very tight; just enough that it won’t back out with use.

Reassemble the lens elements.

Reassemble the lens elements.

Reassemble the brass washer.

Reassemble the aperture indicator ring.

Reassemble the focusing section.

This ring connects the two halves.

Tighten the ring with the spanner tool.

Tighten the set screw in the original factory indent. Again, this should be tightened just enough to hold and not back out.

Screw in the aperture indicator ring set screw. The pin must go into the hole in the brass aperture ring.

Attach the depth of field indicator ring/helicoid/m39 mount.

Line up the holes with the brass focusing ring.

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