How to disassemble the Canon EF 50 1.8 II lens

If you have to clean the lens glass from inside, if you hear strange noises inside, if the focusing ring is stuck, if you have to “repair” it, if you’re plain curious, then there’s no problem, you can take this lens apart and put it back together after you’re finished. It’s pretty frustrating to start doing it if you don’t know where to start and what to do next. That’s what this page is for.


First of all, this is a cheap lens which means its design is very basic with only a few parts. If you’re reasonably handy and careful, everything will be all right, not many things can go wrong. For a detailed view of the lens take a look at this EF 50 1.8 II parts list.

To start with let’s take a look at what we will end with after we have taken the lens apart.

As we can see, not so many parts and actually we can take it apart in under 15 minutes.

The only tool needed for the disassembly is a small screwdriver. Also, use a small box of the tiny parts.

So here’s the lens, before we start the surgery, and hopefully after we sew the patient back together 🙂

First, we take the rear cover off and unscrew the two tiny screws that hold the contact assy.

Turn the focusing ring so the lens sticks out of the body. Now push the contact assy into the body. Gently pry open the rear cover with the screwdriver.

Removing the rear lens assy. You can do this now or later (see step 3.). Now it’s more awkward, later is messier.

Turn the focusing ring so the rear lens assy just sticks out of the body. Grip the barrel of the lens assy firmly with the fingers and take care not to touch the glass. Firmly but carefully turn the assy counterclockwise just a bit and then take it out. If it doesn’t budge try harder but still carefully, it will come out. When the rear assy is out I suggest you put it someplace safe, take care not to scratch the convex side of the glass. Same goes for all the delicate parts.

Put the contact assy in the body and close the rear with the lens cover.
Pry off the switch panel which is glued to the body. Start at the extreme bottom end near the switch. When you’ll put the lens together you’ll replace the glue with two-sided sellotape or you can use the remainder on the panel, you decide.

Unscrew the metal limiter that you can see where the switch lever comes in the body.
Turn the focusing ring so the lens recedes in the body as far as it goes. The ring will now turn a bit more because there’s no stopper. Take the barrel assy out of the body.

You can only put the barrel assy back in the same extreme focusing ring position, remember this when you put the lens together.

The above image still has the rear lens assy attached, if you decided to skip step 3.
In the inside of the body, there are 3 ways for the barrel assy which are covered in white grease. If anybody knows what type of grease this is, please let me know. Some of this grease is also on the barrel assy so take care not to be too messy.

Detailed view of the main barrel assy.

If you skipped step 3, go back to it. Now you have better access to the rear lens assy, but have to grip the front greasy part more carefully, not to break anything.

In the two opposing recesses of the barrel assembly, there are two spacers, covered in glue. Scratch the glue off, and take the spacers out.

The purpose of these spacers is primarily to void the warranty if you messed with them 🙂
The other purpose is to prevent the front lens assy coming out of the barrel.
Removing the front lens assy. Between the front lens assy and the barrel, there’s a narrow gap. Use it to pry these two pieces apart.

Voila, the lens is apart, now you can take the focusing ring off the front lens assy.

Here’s a detailed image of the main barrel with the iris aperture partly closed. There is a small lever with which you can open and close the aperture. You can feel the discrete positions of f stops that are built in the aperture.

The main barrel still consists of many parts, but access to these is quite obvious.

Here are all the parts you should have lying on the table.

Time to put the lens together

Basically, go in the reverse order.

Putting the front lens assy with the focusing ring back on the barrel is tricky. You have to use a lot of force and be careful not to break anything. Before you put them all together check the correct position of the front lens assy and focusing ring in relation to the barrel. It looks as if there are two ways to put it together, but there’s only one.

I didn’t put the spacers back. The barrel assy is pretty rigid as it is, but if you feel safer go ahead and put the spacers back in the recesses.

Before you put the barrel assy back in the body, the focusing ring must be in the most recessed position.

If everything went according to plans the lens is as new, and there are no spare parts lying on the table


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