A little while ago, I wrote about fixing the zoom ring on the Tokina SD 28-70mm lens that I got with a parts camera. Fixing the focus ring took a little more effort, and it needed to be done during the day so I could test infinity focus with a distant object, but it followed roughly the same principles.
As with the zoom ring, the focus ring was held together by scotch tape as suggested in this MFlenses forum post. The scotch tape’s adhesive had degraded to the point it was a slimy mess. However, the focus ring’s function is a little different. Below the focus ring rubber is a join between two parts: the rearmost is a metal ring that bears the distance markers and the focus stops, and the foremost is a metal ring that forms part of the front lens group’s mounting (on this lens, the front group rotates when focusing). The ring with the markings can come away from the front ring and move a considerable way down the lens barrel, which lets the front group move freely. Calibration of focus depends on sticking the two rings together in just the right alignment, ideally aligning the infinity marking with the correct focus stop when the lens is perfectly focused at infinity.
Because the ring with the markings can move a long way down the lens barrel, the scotch tape adhesive had a lot more scope to get into the wrong places. It soon became evident that I needed to remove the front element to clean it all up. And it’s just as well I did — it seems that someone had attempted this repair in the past, as there was a great big fingerprint on the rear lens element of the front group. I hadn’t noticed this when inspecting the lens optics, but I was grateful for the opportunity to clean it up.
Once cleaned up, I reattached the front element (I don’t think I got the alignment correct, but as the front element rotates on this lens I don’t think it matters greatly), then put it on a camera and went outside. I focused the lens on an apartment block about 10km away by rotating the front element directly, using the camera’s split image to get a decent focus. Then, I aligned the markings ring with the infinity focus stop and used a small piece of scotch tape to fix it in place. Then I checked by focusing on closer things then back to the apartment block, and also by focusing at 28mm zoom instead of 70mm. I got it as close as I could, erring beyond infinity slightly if anything.
I fixed the ring in place more securely with two more pieces of scotch tape, then put the focus ring rubber back on. This one hadn’t stretched like the zoom one had, so it didn’t need any padding.
With both rings repaired, the lens is now basically back to normal. It’s not the most amazing of lenses, and it has a strange rotational feeling when taking a photo (possibly the aperture mechanism is a bit out of alignment), so it might need some further work. However, it’s much more usable than when I got it, so I count it as a win so far.
3 thoughts on “Tokina SD 28-70mm lens focus ring repair”
I have the same lens (only for Olympus OM) and it has a sticky aperture, so I can olny use it fully open. The aperture mechanism itself seems to work fine, at least when I use a small screwdriver to move the little lever inside the lens it closes with a bit of a resistance. The blades themself look a bit oily so I would like to disassemble it and clean them but so far I had no luck: First I tried removing the mount and get in there from the back, but I don’t see a way to get the back lens assembly out; then I tried from the front by removing the front lens and then the first two front assemblies, but I hit a dead end after that as I could not remove the lens underneath.
Do you have any tips how to get to the aperture blades? There are some small screws around the outside but until now I have not dared to remove them. Though I have successfully cleaned the blades on some older fixed focal length lenses, this zoom lens looks a lot more complicated and daunting to me!
I’m afraid I haven’t gone that deep into the lens (or into any zoom lens, truth be told). So I’m not sure I could help with that situation beyond some simple observations, which no doubt you’ve already made yourself: 1. on my lens, the rear group is moved when the lens is zoomed, and 2. the aperture appears to be contained within this floating group. The FD mount’s aperture controls connect to long rods parallel to the long axis of the lens inside the barrel, so that they can operate the aperture at any point in the floating group’s travel. That, or it’s in front of this floating group. So, my gut feeling is that the zoom mechanism would need to be dismantled. If I recall correctly, the zoom ring may also be a split ring like the focus ring – you may have already tried this, but removing the zoom ring rubber and splitting the ring might reveal some clues on how to start separating the front and rear of the lens. Let me know how you go!
Seems like a good idea to take a look at what’s under the zoom ring rubber. Next time I have nothing else to so I’ll definitely try to get it off and see if I can get at the aperture that way. By this point I think I have nothing to lose, the lenses are probably out of alignment anyway after I have taken it apart, so it would be something of an exercise in understanding how these old zoom lenses work… 😉 I’ll definitely post my findings here.