On the net you can find all kinds of stories on this lens. Most say its very soft wide open, prone to flare and what else. But most of the time this is merely a side effect from shooting a 40-something year old lens that has gotten hazy inside. Most of these lenses have scratches in the front element coating, which cannot be remedied with this pictorial, but image quality still can be improved a lot by cleaning the lens up.

Wanna see how to get the most out of this lens again? Read on!

In general, there are two problems with the Canon 50/1.2 lens: haze inside, and oily aperture blades. We are going to remedy these issues in one go.

The Canon 50/1.2 is a very easy lens to clean. The whole lens is accessible with just the use of a spanner and a single small jewellers screw driver. It can be cleaned with a soft synthetic cloth, a blower and some Q-tips with Naphta, commonly known as lighter fluid.

In this pictorial you can see some shots on how to proceed. Make sure you read the text inbetween as well, it's still a several hundred dollar lens you will be working on!

I started out with removing the black ring on the rear of the lens with the spanner. As you can see, I'm using an old synthetic soft cloth to work on, so that any dropped part will not bounce off the table, never to been seen again. We wouldn't want that to happen, right?

After removing the rear ring, the whole rear end of the lens comes off in one piece:Leave all the other stuff on the rear end of the optical unit attached, there's no need to get any of it off.

Next, unscrew the rear element. It unscrews counter-clockwise. Just use clean hands to grab the black outside of the rear element. Make sure not to scratch it!

Here you can see the rear element lying on the cloth in front of the lens. Underneath that, there is another element, again with two notches in its retaining ring, so you'll need the spanner again to get that out. The brass ring on the rear of the lens is loose, it functions as a shim to get the optical element at the right distance to the film surface. You can take it off, or leave it sticking to the rear.

We have now reached the aperture blades, and cleaning those is easy as pie as long as you remember not to apply any force!!!

If the aperture is oily but still moves freely (i.e. all aperture blades are looking like they should, nothing dislodged), a good clean will do the trick. In the next shot I have closed the aperture down completely. Use a Q-tip soaked in lighter fluid to moisten the whole aperture with. Make sure only to rotate the Q-tip, clockwise only! If cleaning counter clockwise, the Q-tip will grip the edge of an aperture blade, bending it for sure. Your aperture will be wrecked then!

Let the lighter fluid sit for half a minute, then take the dry end of the Q-tip and again clockwise! clean the aperture.

I usually repeat this procedure for some five, six times. Then, I wet the aperture again, but now carefully open it and close it several times. The lighter fluid will mix with the oil on the blades and dilute it.

Make sure not to force anything, and keep an eye on the aperture while going through all stops, making sure nothing unusual happens. If it does, you're in trouble. This procedure allows for cleaning the aperture from the rear side only, which in many cases is sufficient.

Repeat the aperture cleaning procedure several times more. I spent nearly thirty Q-tips cleaning this lens. One additional trick: the aperture ring couples with the aperture through a narrow slot in the barrel. Here's what you do to clean any excess grease out:

Use small pliers to squeeze the end of a Q-tip until it fits the slot.

Now it fits the slot.

So far for the 'safe'  procedure, cleaning from the rear end only. There's another approach, the more thorough one, which is also a bit more hazardous for the unskilled repairman. We're going to see the shots for that now. If you're uncertain on this, just scroll until you see a green cloth and you'll be safe again. :)

Look for a small set screw on the outside of the rim of the front element. Unscrew this small screw a few turns. Now grip the knurled ring for the aperture,look at the front element from the front, and unscrew it counter-clockwise. This might take some force. Do not use the spanner to remove the front ring on the lens, this is totally unnecessary. The front element and its retaining ring that is part of the barrel front end, unscrew as a whole.

Now, all optical elements are out and the barrel with aperture ring, aperture and click stop spring remains. Fill a small bowl with 3/8 inch of ligher fluid, and soak the whole aperture in it. I used some motion to get the lighter fluid in the mechanism:

You might have found a brass ring coming off earlier when you removed the focusing mount, if it still stuck to the barrel it will most likely come off now. This ring acts as a shim, read before.

There is also a brass ring on the inside towards the front of the lens. If you remove that one, the aperture comes apart. Since the pictorial would at least double in size when trying to address that problem, we'll just leave the ring nicely sit where it currently is, RIGHT!?!?

Once all excess grease and oil is cleaned out, leave the aperture to dry. The lighter fluid evaporates quickly.

Now, start adding the optical elements to the focusing mount again. Screw the front element on, but not tight yet.

Each element you can carefully clean with a synthetic soft cloth:

If you removed the inner and rear element only, clean each of them carefully and re-install.

Use the blower to make sure no dust is sealed in between the lens elements.

If you removed the front element as well, tighten this up once the inner and rear element are in place. Tighten the set screw, carefully. It is made from soft metal. The exact order of these steps made sure on my lens that there was no wobble in the lens barrel upon assembly, any other order left me with a wobbly lens.

Now the lens is ready to serve my M3 again:

In due time I will post some shots from this lens online, and link to them from here. For now, I hope I have helped you out!