What's inside a DSLR lens?

[Jonny69]

Ever wondered what's inside a DSLR lens and how it works? Well while I was away on holiday a bottle of water burst open, partially submerging my camera. Once dried out, the auto-focus was dead and I could see a lot of residue left on the lenses inside the lens body. Figuring it was dead anyway, I decided to open it up to see if cleaning the lenses would make it focus again, in case the camera couldn't 'see' through the residue...

Here is the patient, the kit lens off my trusty EOS 350D:



There are four access screws on the base where the lens screws into the camera. It looks pretty dusty when photographed close up, no wonder I keep getting plagued by dust specs on my pictures:



So I'll be needing my trusty miniature screwdrivers that I keep laid out like this ready for use:



With those four screws out, the cap was loose but wouldn't come off because the ribbon cable under the connectors was not long enough to allow it. It took me a while to spot them, but there are two tiny screws in the side of the connector block, one of which is hidden by the moulding on the base of the lens body:



Those two screws shown on a 1p piece to show how small they are:



Once out, the cap on the base slides off, revealing the control board:



To remove it, the dust shield round the edge lifts off, there are two silver securing screws and the ribbon cables must be disconnected. The backs of the connectors pull out to unlatch them:



And then it just lifts off. The orientation is easy to remember because there are two cables next to each other on one side. Here you can see inside the lens and the zoom assembly down inside. Under the silver plate is the auto-focus mechanism:



The two screws at each end of the auto-focus unit detach it:



Underneath there is a small drive dog that lines up with a matching one that connects up to the front lens, which is the focusing lens:



The next challenge was how to get the zoom assembly out. Twisting the zoom ring moved it up and down but there didn't seem to be an obvious catch or screw to free it and I didn't want to force it. I decided to peel back the rubber grip on the outside of the zoom ring, which revealed four screws with bushes that ran in slots, acting as the stops for the limits of the zoom in and out:



I took these out and it was looking promising, but it still wouldn't come out. When it was at the limit of one end of the zoom, I noticed four similar screws with bushes appear in the hole that you can see at the focus ring end of the lens. These also ran in tracks, but these were helical tracks up and down the lens. I put the other four back in and took these out instead and voila, the zoom assembly now popped out the top:



I call it the zoom assembly; more accurately it's the body for the zoom lenses and the aperture mechanism is inside it. You can see a bit of residue on the lens above, but there was more inside the unit. There were some more screws to get inside and I gave each lens a polish:



You can really see the residue on the inside of the focus lens:



Reassembly was pretty much a reverse of dis-assembly. Canon, being a sensible manufacturer, used the same screws in as many places as they could. This not only reduces costs, but also makes it easier to figure out what screw goes where, unlike when you have multiple different screws in the case of a laptop which is totally unnecessary. There were a few things to line up, notably the slider that controls the aperture and the drive dog on the auto-focus motor:



So that's how it works. Not one dust seal in sight, so it's no wonder these get plagued with dust problems. It's quite a complicated unit though, and mine doesn't have image stability inside like the later model EOS do, so you get an idea why camera lenses are quite expensive.

Sadly, it didn't fix the problem. The auto-focus motor seems to have been damaged and it needs help. If I help it by turning the focus ring while it tries to auto-focus, the camera recognises when it's in the right place. Time for a new lens, but it was fun taking this one apart

[LeperousDust]

Can you not procure parts and replace the motor? Since you've done all the hard work once!

[Toby]

Fascinating! Thanks for that

[Jonny69]

Originally Posted by LeperousDust

Can you not procure parts and replace the motor? Since you've done all the hard work once!

I had thought about it but the focus ring is really worn on this lens and it's got a couple of degrees play in it. I'll just replace it.

[Toby]

You can pick up the kit lenses pretty cheap if you look around, although get an IS one if you can, they're much better optically than the non-IS ones.

[Desmo]

It's always interesting when things break and you start to dive in. I always remember my Walkman breaking down on a school skiing trip. I took it apart on the coach with a scalpel and fixed it

[Justsomebloke]

I Love you Jonny69. + =

[Nutcase]

You had a scalpel on a skiing trip?!

[Justsomebloke]

Originally Posted by Nutcase

You had a scalpel on a skiing trip?!

He's from Essex.

[Nutcase]

Ha ha true