Repairing Canon EF 80-200mm F4.5-5.5 Zoom Lens

This is a Canon EF 80-200mm F4.5-55 zoom lens which had water damage/mess on the internal lens elements. Other than grubby lenses this lens work fine so should be simple to fix! First thing to to is take off the rear mount. There are 5 screws on the back plate and 2 hidden ones which hold the connector contacts in place. The mount twists as it comes away. The AF/MF and tricky to get off and real pain to get back on so engages with the mechanism. The screws are #00 Phillips and pretty poor quality. The lens already had a head snapped off one of the rear screws and 2 rounded off inside the lens from someones previous attempts to take is apart. One the tabs are pulled back the connectors pull out and the board comes away. Underneath is the AF motor mechanism, this is held on with 2 screws and simply pulls out. The rear lens element simply unscrews and comes out. Under this is a random springy piece of metal (which I assume this helps stop the rear element unscrewing). The next element is held in by 3 silver screws with a large diameter head, these screws are very poor quality and very easily rounded. Next the front end of the lens is dismantled. The ring at the front of the lens just clips out - there is a small notch to insert a screwdriver. The front element then slides and comes off. There is then a black cover piece which sits in front of the aperture mechanism held on by 3 screws.

I didn't bother taking off the aperture mechanism as the ribbon cable is threaded right through the body to the board at the rear.
Now we can access all the elements to clean them - there is still one element in the lens but this is easy to reach.
Assembly was pretty simple apart from getting the AF/MF switch back in the correct place. The construction of this lens seems pretty cheap and flimsy, it wasn't obvious how to completely strip the lens but I assume there was clips etc.

Fixing Sigma M42 80-200mm Zoom Lens

This old lens had a very sticky aperture and slightly dirty glass - a great excuse to taking it apart to see how it works! First to come off was the rear mount section that attaches to the camera, this has 3 screws which are either anywhere between #0 and #00 philips depending of the quality of your screwdrivers. The screws used throughout the lens appear to be the same head size. Once the back is off you can see the arrangement for controlling aperture, with the back off the lens is in manual and sliding the levers will move the aperture (or not in the case of this lens). After removing a few screws the whole mechanism lifts off. The rubber grip pulls off to reveal a piece of silver tape that holds the two halves of the outer body together. This lens is push/pull zoom and rotating the body alters the focus. It is the end element that moves to focus and this runs on the threads. The lens consists of multiple sets of elements with lugs (nylon disks held on with screws) around the edges. These lugs run in carefully designed and machines grooves in the outer body of the lens. When the outer body is moved the grooves act on the lugs which, in turn, move the elements to give the desired zoom. With the tape off and the first couple of lugs out the outer case comes off. The grooves the lugs run in are now visible. Taking out more of the lugs allows the lens to come apart. The lens is arranged in 3 main outer cylinders which have grooves to move the elements. The elements have 2 sets of lugs, the first hold the lens in place while the second move the element as the body moves. Some lugs run in 2 different cylinders so pretty complicated! Is a pretty simple arrangement with one pin on each side of each aperture blade which run in grooves. Most challenging part was putting it back together as everything has to line up correctly, this took a lot of looking back at pictures (plus some trial and error...). Without taking pictures it would have taken a *long* time to get it back together - there were different size and shape screws and lugs etc. Back together the lens worked great - even with all the grease cleaned out of it!