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Vivitar (komine) 70-210mm, PK-A mount, sticky iris repair.
Posted By: marcusBMG, 05-22-2016, 09:25 AM

These notes are supplemental to the notes (pdf) downloadable from [update 2023 this website seems to be defunct - may be findable as an archive, or in case of need, I have downloads of many of teh repair pdf's) for a CFD mount lens. They are an abbreviated, overview acount of disassembly for iris cleaning, with specific detail for the PKA mount.
Tools: JIS and flathead screwdrivers, special DIY tool for unscrewing the union ring, solvent for iris cleaning. Lens spanner not required.

1. Remove the plastic aperture lever protector from the mount (3 x JIS), and pull out the cylindrical light baffle underneath. You can now see a spring SP (pic 1).
2. Unhook the spring from a screw Sc. Thin fuse wire bent into a hook can be good, or a small jewellers screwdriver may be sufficient.
3. Now proceed with mount removal as per Mel's notes from
4. Remove three JIS screws to slide the index ring forward (p8).
5. Loosen three set screws in the aperture index ring (with the red dot) (p10). Now this ring and the f-stop marked ring will be able to slide forward. NB remember to catch the detent ("clicks") ball bearing, it is right next to the red dot, and the wee spring in the hole.
6. Three x JIS screws are now exposed, remove these and the whole bayonet mount will come off. It's a close fit, so ease it off (p11). First time round this is when I had to unhook the spring, but with hindsight it is easier and better to do that first as per #1, 2.
7. Unscrewing the union ring is the most technical part. Read Mel's notes (pp 12-13) and pay particular attention to marking a guide rail and making connect/disconnect marks/scratches. I used a feeler guage to measure the gap between the union ring and the bump ring - 38 thou. As you can see in pic 2 I made a diy tool. This was necessary, it was pretty stiff to move the union ring on my lens. The tool is made from a ~1" piece of heavy duty pvc pipe reinforced with Davids Isopon/similar filler, which made a thread for the two bolts, ends shaped with a dremel. Although the unit still isn't very rigid that is actually beneficial, I can place the tool into position by squeezing it gently.
You can observe the disengagement of the 3 brass rails (that prevent the mount side from rotating with the union ring for the first ~50% of the unscrewing) from the mount end through the gap between the rear optical group and the mount end (actually it might be possible to unscrew and remove the rear optical group at this point which would make that much easier). Once these rails have disengaged the union ring and mount ring screw off readily by hand in unison.
8. Prime lens assembly (rear optical group + iris) is held in by 3 x round head JIS. The rear optical group unscrews from the iris assembly, loosen this while it is still in the lens.
9. My first cleaning was unsucessful, the iris was still sticking after reassembly, even though it had seemed snappy enough. I had tried some spray PCB cleaner - C6 iso-alkanes. Second time round I soaked it in coleman fuel as well - success! UK readers can note that a substitute for overpriced coleman fuel is "panel wipe*".
10. Reassembly is a straight reversal of 1-9. The icky stage is the re-engagement of the guide rails as the union ring is screwed back on. The rails can be observed from the mount end, my impression is that one is slightly longer, once this one is enaged the others will do so naturally. A bit of wiggling and to-and-froing did the trick. The main thing is to check that the guide rails go back into the correct guide slots. Provided nothing else has been rejigged the lens will end up naturally as it was, checkable with the feeler gauge.
One minor hang up was the lens focus/zoom ring moving back enough for the long aperture actuation lever to come out of its slot while the union ring was being worked with (p14, photo J), necessitating placing the lens on its front end and a little fiddle with a screwdriver to gently re-engage the lever with its slot.
11. Replacing the mount: the screw holes need to line up but also there is a small silver stud SS (pic 3) that has to engage in a stirrup St. It's a bit fiddly because the spring loaded aperture lever on the mount needs to be held to keep the connections clear of this stud so that it can engage.
12. Line up the aperture rings, replacing the detent ball bearing and spring. The f-stop ring is aligned by a slot that needs to engage with a small metal tab on the mount. The "spot" ring is lined up by eye with the infinity marks on the lens and by eyeing the "click" slots for the detent ball bearing.
13. Refit the index ring before tightening the set screws on the aperture index ring. Note that the aperture won't click correctly into "A" until the spring has been reconnected. Fine tune the alignment of the red dot on the aperture index ring with the white line on the index ring, test the "clicks" and finally tighten the set screws on the aperture index ring.
14. Finally reconnect the spring disconnected in #2 - hook the loop end onto a small jeweller's screwdriver and use a second screwdriver/toothpick etc to push it over the screw. Replace the baffle and aperture lever guard. Test and fini.

Overall a medium difficulty operation, well within the compass of anyone who is prepared to get to grips with a bit of lens diy.
*But note that the type of panel wipe required is the petrol (hexane) based one, not the alcohol or water based one.

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Last edited by marcusBMG; 05-05-2023 at 10:29 AM.
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05-22-2016, 11:48 AM   #2
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QuoteOriginally posted by dcshooter Quote
Great writeup! An easier to find and safer solvent than hexane-based ones is regular naphtha lighter fluid. As with any organic solvent, use only in a well-ventilated area with no ignition sources nearby!
Thanks Brian. Not found naphtha easy to get hold of this side of the any case its not that different they're all petroleum distillates.
05-22-2016, 09:58 PM   #3
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This is a great post. I have had several of these and all had the sticky aperture. One I ruined by trying to repair it myself. Another was destroyed by a "repair place". The third may get some new life after all.
05-23-2016, 06:29 AM   #4
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If anyone needs the diy tool I made msg me (UK)


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70-210mm, aperture, boggys, dissassemble, iris, jis, komine, lens, lever, mount, notes, screw, screws, sticky, union, vivitar series 1
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