Fixing a stuck focus ring on a Canon 50mm f1.4 lens

So a few months back disaster struck, I managed to break my 50mm 1.4 lens! Focus completely jammed - couldn't even manually focus. gutted. I took the lens to my local camera shop and they said they would have to send it off to Canon and it could cost up to £180! Ouch.

Having just forked out for xmas, car insurance and about a gazillion other things that wasn't a particularly inviting proposition. So in some what of a bold move I decided to take matters into my own hands.

After a quick web search it became clear that this fault is actually quite a common problem with this particular lens and is caused by an arguably dubious design choice on Canons part.

Disclaimer
What follows is a guide to what I did to fix the problem, I am not a professional repairs person and I am not for one minute saying this is the best way to fix your lens, but it worked for me. This is a delicate procedure that could easily go wrong and if you try this yourself you do it entirely at your own risk. If you are in any doubt, send it to a professional.

Tools
To dismantle the lens you'll need PH0 & PH00 precision screw drivers, also useful will be a scalpel, fine tipped tweezers, lens cloth, some sort of tray to put bits in & a pen and paper. 

In order to fix the actual problem you want a good quality digital calliper and a hammer. Yes that's right you'll be hitting you beloved lens with a hammer. There are other ways to do this and I'm sure there are much more professional, efficient and expensive tools for the job. This is simply how I chose to attack the problem (literally!)

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Feeling reckless?
Good, then we shall continue. Clear a large brightly lit area, lay out your tools and place the lens in question on your lens cloth.

As you are working I would highly recommend keeping all the various parts and screws labelled and possibly in separate containers. 

Read this guide through at least once before you begin and make sure you have all the tools needed to hand.

Step 1

Remove the 3 screws around the top of the lens. you can now gently remove the front casing and focus ring by sliding them off the end of the lens. Notice that there is also a small clear plastic ring just underneath the front casing. remove all these parts and put them to one side.

Step 2

Turn the lens upside down and remove the 4 screws marked in red. The silver lens mount is also attached to the body with some tacky resin, take your scalpel and very gently prise the lens mount loose. I say gently because the small part with the gold contact plates is attached to the base plate and the lens body by a contact band, if you damage this connection you will most likely ruin your lens entirely. At best it will no longer be able to communicate with the camera.

Step 3

This is one of the trickiest parts to the procedure. Lift the lens mount on the opposite side to the gold contacts and you will see that the black plastic inner ring is attached to the metal mount with 4 plastic 'hooks'. What you need to do is gently but firmly prise these off the metal mount with a small flat head screw driver. This is particularly difficult because you'll need to use some force but be very careful not to (a) snap the hooks off & (b) damage the contact band attached to both lens and mount.

If you can prise 2 of these hooks open the inner plastic part should come free.

Step 4

Next remove the two screws marked in red, but not the one marked in yellow. You can now remove the metal mount plate.

Step 5

Ok, now we're gonna remove the little panel that holds the AF/MF switch. This is secured in place with a little blob of glue so start by cutting through this with the scalpel. Once done carefully slide the panel up and out. I say carefully because there is a very small switch behind the panel that could be easily damaged (see pics) What you'll want to do is push the panel up a touch and then tilt the bottom of the panel out a touch so that it can clear this switch. Once that's done you can slide off the last bit of outer casing (the bit that says '50mm' on)

Step 6

Now we need to detach the contact band pictured below. Take your tweezers or scalpel and slide the little white braces out in the direction indicated. They should slide out quite easily by about 1-2mm, once done the contact band can easily be removed from the socket.

Step 7

Remove screw and contact plate indicated below

Step 8

Remove the white plastic runner guides, there are 3 and they will all need to come out.

Step 9 

That contact band that we detached in step 6 is also attached to the body with a blob of resin glue, at this point you need to very carefully prise this free. I gently pulled up on it and cut through the resin with my scalpel. Once done you can slide off the main housing as illustrated, threading the contact band through the gap as you go (its attached to the inner lens housing)

Your beloved lens will now look like this... (scary huh?! lol)

Step 10


We're nearly there and you can now see what the actual problem is. Remove both white plastic guides (circled in red) and slide off the guide slot housing. Where the guide slot meets the top of the housing the metal is VERY thin, it would seem that even a small amount of pressure on the front of the lens can cause this to bend out of shape. You can see quite clearly a large bulge at the top of the housing where it should actually be flat.

Step 11

Now all you need to do is bend that housing back into shape! Well, I say all, this is actually quite a tricky job. That guide slot is precision engineered and needs to be exactly the same width all the way along. Which is where your digital callipers come in!

There are quite a few ways of bending the metal back but its vital that you take repeated measurements all the way along the gaps (there's one on each side of the housing) as you are working. your aim is to get those gaps as even as possible all the way along. Even the slightest deviation will cause problems in focusing - most commonly either being sluggish or getting stuck at certain points.

Before you start bending run the housing under a hot water tap for a few minutes, this will make the metal more pliable and easier to work with.

In theory its possible to take the silver metal bracket off, although mine was so ridiculously tight I could not do this. If you can you could try putting the housing (bulge down) on a hard flat surface and pushing down on it to straiten out the metal.

I resorted to putting a flat piece of metal over the bulge and tapping with a hammer, which actually worked pretty well. you could also try putting the whole thing in a vice. Like I said at the beginning, there are probably precision tools for this sort of thing, but I neither own, nor know anything about such tools.

Finally

Once you're happy with your bending and straitening efforts simply follow the steps in reverse order. If the lens is sluggish or gets stuck at certain focus points do the whole procedure again (it took me 2 attempts)

When you're reassembling, bear a few things in mind ~ make sure you don't over tighten the white plastic guides (steps 10 & 8) if they are too tight it will make focusing sluggish. Also if the camera has trouble communicating with the lens try tightening the four screws in step 2 and/or cleaning the gold contact points.

Good luck!

Resources

There are a number of articles and discussions about this procedure that I used to learn how to do this. My aim with this post was to compile the best of this information in one place, hope you find it useful. Here's a number of other places that this is being discussed...

http://www.clubsnap.com/forums/canon/919440-fix-dropped-50mm-f1-4-ef-lens.html
http://www.fotomozaic.ro/artikel.php?idstory=225&s=1
http://www.clubsnap.com/forums/canon/475106-canon-ef-50mm-f1-4-disassembly-procedure.html






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