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Kiron/Vivitar 28mm f2 (24mm f2) sticky iris fix
Posted By: marcusBMG, 08-21-2019, 12:43 PM

This is not a full write up. Having just gone through freeing up the iris on my kiron 28mm (update: and on a FD mount vivitar 24mm f2) I decided it would be handy to have the info in one place.
There are already several threads etc around to refer to:

Kiron Kino Precision 28mm f2.0 aperture issue - - 3 page thread from 2009, resurrected a few times by posters seeking more info, useful pics and discussion.

Kiron 2/28mm disassemble - mflenses thread discussing some of the problems, specifically stuck optical groups.

CLA Kiron 28 f/2 part #1/4 | Boas, antes de mais, CLA signif? | Flickr - flickr pics and full disassembly write up by Paolo Gomes with English translation (scroll down).

Update 2: the Komine made 28mm f2 is pretty simlar see this thread.

It's clear that there are variations in the structure of these kino optical 28mm f2's. I think mine is a later Kiron (serial 60103134), PKA mount. Pic 1 below shows the main parts:
  1. Mount and baffle
  2. rear optical block
  3. front optical block and cover/nameplate.
  4. Focus/distance scale ring.
  5. helicoid and iris assembly, mount side, front side pic 3. Note the PKA contact sits in the recess in the alloy perimeter at 10-after.
The job in essence is straightforward, an easy diy: remove the mount and rear group , remove the front group (both optical blocks just unscrew, no lens spanner required), iris is now exposed from both sides and can be cleaned. In practice it can be problematic. My first mistake was to try to unscrew the front block without realising that it is more likely that the front cover/nameplate is in fact going to unscrew. This is what happened but because I hadn't loosened the locking grub screw GS (see pic 4) the thread got a bit chewed up. Next (normally - in order to get better grip of the front optical block) the focus/distance scale ring can be removed, that's just 3 JIS screws. Note that the position of this ring on the helicoid sets the infinity focus stop, so it's a good idea to reach in with a long pointy something and make scratches to mark its position. It's not difficult to reset the infinity focus stop after though. Next the front optical block. This seems to be regularly sticky. On my lens it turned out that there were 2 access holes for thread locker solvent (pic 5), a dribble of acetone left for a few minutes in these and at the joint, and a strap wrench, did the trick.

I next removed the mount, this comes off as a unit with the baffle, note that the click ball bearing is under the next ring which I didn't need to remove. Note the PKA contact however is loose. There was no "bronze ring" referred to in the other threads on mine. The mount does need to be removed in order to get a grip on the rear group to unscrew it. Once again judicious use of thread locker solvent was key, I used a pair of pipe wrench grips with the rubber strap of the strap wrench providing cushioning.
I used coleman fuel and some iso-hexane contact cleaner spray to clean the iris, small brush, tissue. There is a tab T to manipulate the iris see pic 2. Iris must be totally snappy, no hint of hesitation.
Re-assembly is simple reversal of previous. The one ticklish bit was replacing the mount - the PKA contact kept jamming. Set the lens aperture on "A" and the contact in its elevated position in line with a gap in the mount rim. Manually move the mechanical aperture indicator (opposite the aperture lever) so that a wee tab engages in a wee slot and the mount lies flat before replacing any screws..

The 24mm F2 proves to be essentially the same structure as the 28mm. The helicoid is more complex, but you don't need to separate that unless you are completely disassembling. See
if you need beta on taking off a FD mount.

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Last edited by marcusBMG; 11-16-2019 at 01:03 PM.
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08-21-2019, 03:48 PM   #2
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Nice article on a great lens. I had one, sold it, and regret it. Hopefully your article will help people save some of these lenses.
07-13-2021, 10:23 AM   #3
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I have been able to find Paolo's Part 1 and Part 4 instructions on Flickr. For some reason the go to Part 2 link takes me to an unrelated photostream.

First time, I found myself at Part 2 but couldn't get back to 1. if I can find my way back to #2, I may be ok...

Or ask if there is an easier link that has all 4 parts grouped.

Thank you
07-13-2021, 11:53 AM   #4
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If you find the parts, do post the links.

07-14-2021, 01:46 PM   #5
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QuoteOriginally posted by marcusBMG Quote
If you find the parts, do post the links.
I will.

Meanwhile, I can't get deep enough inside the back (mount removed) with a rubber strap wrench to loosen the entire rear cell...I only loosened the retaining ring for the rearmost element...not at all what I wanted to do.

I was able to remove a little surface grease and get the iris to move slowly. Slight improvement that at least proves that's the problem.

The blades are just swimming in grease...I've never seen one that bad.
07-15-2021, 07:42 AM   #6
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IIRC I used repeated little doses of acetone on the join to loosen thread locker, and having a right old fiddle with water pump type pliers (padding on the jaw) to get it loose. Also try judicious warming (radiator/hair dryer).

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