I had one of the famous AF 28-135mm f4-4.5 lenses arrive today. It came attached to a 7000i which is as boring in person as it looks in photos. The backlight in the LCD is kinda cool, I guess...
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There was stuff wrong with the lens, as usual. Some haze on the inner elements, a weird smudge too, and the front element looks like it'd been dropped onto rocks and has a few chips out of it.
Disassembly was with help of photos from pbase and the service manual on archive.org.
Camera repair guide
archive.org
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Full of dust under the covers, but also the dust seals seem to have mostly done their job.
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The aperture sits between lenses G8 and G9 in that optical diagram on page 5 of the service manual, and I've no idea how you'd reach it. Fortunately I didn't need to go that deep. But I did spend a bit struggling to get the 4th lens barrel out, the one with elements G12 and G13.
There's archways in the part the manual calls the 'lead groove barrel' for removing the 3 cam rollers holding that element in place. You use the same archways to access another set further down but I didn't need to take this one apart that far. You line them up by messing with the zoom and focus adjustments.
The problem I had was that the archways are only big enough for the screws to come out, but not the rollers around the screws. But because of the old oil between the both, the screws were kinda stuck inside the rollers. It took alot of fiddling and using a screwdriver tip from the inside to push on the little bits of exposed screw threads to get the things to come out far enough. When till stuck to the rollers the tips of the screws were still just in the screw holes and holding things in place.
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The surface of element G11 there on the left was filthy and i've no idea why. G12 opposite it was spotless. Maybe a gravity thing in how it was stored or a degrading coating? It looks like there's some wipe marks on it that weren't from me.
On the right is the opposite side of the aperture, G8, where it looks like some kinda groady wet flake got inside. I cleaned it off before I thought to take a photo but you can see its remaining residues on the metal. I figure it must've sat on the lens for a bit before falling off and sticking to the metal and drying.
After that I reassembled the thing. It seems like it'd be a minor ordeal if you had to reach the aperture for any reason. The service manual isn't super clear on some stuff, I feel.
Well at this point in writing the post I figured I should check the infinity point and found it was way off.
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After some fiddling and confusion, the way it seems to work is that the two halves of the focus mechanism, the focusing ring and the cam tracks, are coupled together with that length of white tape. It had me confused for a bit because I thought maybe something had dropped out that I didn't notice, or i'd reinstalled parts wrong. Load bearing tape seemed a little odd after everything else is made from milled slabs of aluminium at great expense.
But thinking about it, it's really not a bad idea. It seals the inside from dust, it's easy to adjust (you peel the tape off, slide the two halves, and put the tape back on), cheap to replace if needed, and the more normal method with 3 tiny pointed screws tends to be awful (slips easy, leaves gouges and divots, hard to make tiny adjustments since the screws want to re-find their old divots, can come loose with time, easy to damage the tiny screw heads or wear out threads, distorts parts from round to triangular...)
The manual might clearly state it's the tape that mechanically couples the two halves, but I overlooked it if it does.
Also I had to open the lens again because there was another problem i'd either not noticed or caused myself. At longer focal lengths the focus got stuck hunting/ rapidly oscillating, overshooting the focus point. A guy called John in the comments of pbase had the same one, with bent spring contacts in the part of the board that senses the current focal length.
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They're visible from the outside of the assembly, which is fortunate cuz the 2 screws that need removed for it have wax seals on them, so i'd rather not have touched them if I didn't have to. I scratched the outline of the mating part (2553-1382-01, brush connecting plate) to help get it back on in about the same place.
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They were then carefully bent back. That John guy on pbase had his snap off when attempting this so I was being very cautious. I've just realised what might've caused it too - when reassembling and disassembling stuff repeatedly to try figure out earlier problems, the finger of the brush connecting plate mustn't have gone into its matching hole while the screws could still engage and pull the parts together. The brush plate is made from something springy if that is the case.
No idea what would've caused those dents in the gold traces though. But ether way, bending the brushes back finally fixed the lens and now it works fine... I think. I've no digital full frame cameras to really test it, so i'll just have to see if it can do Kodak Colourplus in months old used chemicals justice.