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MD 28-85 Question: Help with loose/wobbly focus ring/front assembly?

  1. xo-whiplock
    Just received a Minolta MD 28-85mm Zoom and found the focus ring to be loose and wobblly a bit. I can focus fine if carefull. The loosness is at the bottom side of the lens when framing a shot. The top is much tigher. As long as I don't push up on the lens, it will focus fine. However, I would like to fix this loosness. I tired to figure out how the lens could be accessed to determine what needs tightened, if anything, but just looking at it I can't tell. If anyone has experience with this lens and issue, I would like help in understanding what it could be, and if it's someting that can be tightened; or does the problem indicate a worn or broken internal part that needs replaced to fix?

    Thank you for any help

    xo-whiplock

    SRT101,102,XE-7,X-700 and working on finding good sample lenses.
  2. upnorthcyclist
    upnorthcyclist
    Boy, the symptom you describe doesn't sound good. The problem that I've run into with manual-focus Minolta lens repairs is that it generally costs more to have them professionally serviced than what you can pick up another copy for, unless it's one of the "must-have" collectors' items.

    These two-touch lenses usually have an internal, slotted sleeve in them, that is moved in and out by the zoom control ring. The focus control usually has a couple of pins that ride in the slot of this sleeve - it all moves as a unit. It is common to have a little looseness in this system - it seems like, because of the complexity of the movement, if everything was tight, it would bind. Maybe one of the sliding pins has broken or fallen out of place.

    Since this lens is variable-aperture, it is much simpler inside than a fixed aperture lens, because the aperture doesn't have to be compensated as the focal length changes, either by changing the aperture itself or by complex movement of the elements. I guess if I were in your position, I'd adventure into the lens and see if I could fix it, although with the full knowledge that I'd probably end up with a pile of junk at the end of the day...

    Mike
  3. xo-whiplock
    xo-whiplock
    Mike,
    I'm doing just that right now. I'm taking pictures as I go. You are right, the guide pins on 2 of the 3 seem to have lost their guiding ability. Most likely due to wear of some kind of bushing that most likely mounts around the pin. I have it apart all the way down to the apature assembly and tube at this time. I'm taking a break to reply. I'll post the pics and the process for others. At least I'll be able to clean all the lenses with my new LensPens(TM), even if I can't cure the guide pin issue. Should be done taking apart soon.

    Craig
  4. upnorthcyclist
    upnorthcyclist
    Bravo!

    Keep us posted on your progress, and good luck!

    Mike
  5. xo-whiplock
    xo-whiplock
    Well, a good ending to this story... I took apart the lens and found 2 of the pins had worked their way loose. The loosest one was just barely haning on with a couple of threads. I ended up taking everything off, except for the apature and lens assemblies on either side. It was a puzzle and after completing it, I checked infinity and looks good. There is just the slightest bit of wiggle in the focus/front assembly, but that's because I didn't have new pins/nylon washers to install. I simply moved them all to different spots and eliminated most if not all the wiggle. Very usable now. About half way through, I relaized that the job could have been done without taking the back mount off, and could have fixed it from the front end and middle/outside.

    Steps:
    Start by extending lens all the way out, and take a picture of the lens so you can see all the markings for lining up them again later.
    1. Remove focus grip.
    2. Remove tape under grip.
    3. Unscrew top focus ring counter clockwise.
    4. Remove 3 screws and lift out metal washer plate.
    5. Lift up and off the lower focus ring, carefull not to turn front element.
    6. Mark the side of front element's metal mount and side of tube with a horzontal and vertical scribe giving both correct depth and alignment of front lens assembly for re-install.
    7. Unscrew the front lens assembly counter clockwise and remove. (Opptional) You can leave this in if you want, but you may damage glass. Up to you.
    8. Remove zoom rubber grip.
    9. Remove the two silver slotted screws.
    10. Turn the zoom ring and look inside of the other holes as you turn to find the black philips head screws. With one lined up, the others will also be lined up with holes. Remove these screws and the plastic tube with the colored lines on it should now be free to slide up and off.
    11. Slide the plastic tube that the these screws were holding up and off the lens.
    12. At this point, you'll see the zoom guide pins. Check for looseness and tighten, and if still too much play, move them different positons.
    13. Reassemble in reverse order.
    14. Check that your marks line up, and if not remove and try a differnt starting point, and repeat until marks line up. It helps to have another mark on the ouside of the tube just at the point there one of the groves of the threads exits, so you can match up the begining of one thread on the lens assembly to that mark with starting to thread the assembly in. Take your time and when you place the assembly down onto the lens tube, turn it backwards first until you feel the assemble drop down every so slightly into the threads, and then try to move it forward (clockwise) gently and see if it will start. It take some practice and some time to get the feel for it. It's not like screwing on a nut to a tappered headed bolt, more like starting a nut on a freshly cut piece of threaded rod. It can be done, but it take time to find just the right spot to get it started.
    15. Once the marks line up for both height and rotation, do not move the assembly when putting the lower focus ring back on with it lined up at infinity.
    16. You may have to rotate the zoom ring, as I put my silver pins/screw in the oppisite holes the first time. Just take them out and turn it 180 deg and install again.

    Note: Cleaning the lenses is a good idea. I used a LensPen(TM), and a rocket blower to keep the dust down.

    Let me know it this helps anyone, or if I missed something, as I'm writing this from memory and revised it to eliminate my wanderings.

    Craig
  6. upnorthcyclist
    upnorthcyclist
    Good job Craig!

    It is especially helpful to note that this repair can be accomplished from the front of the lens.

    As i mentioned in another thread here, I bought an XD-11 last year and have been doing a modest upgrade to my Rokkor lens kit to some MD-style lenses. For the most part, I have had good luck in the quality of the lenses I have won on the bay or purchased from KEH. But, I've gotten a few losers from sellers at auction. I decided at some point that I would have no tolerance for equipment that wasn't as described, either by misrepresentation or omission. When I receive a lens or other piece of equipment, I give it a thorough look-over, shine a penlight through the optics, mount it and run through ts functions etc. If it is not to my satisfaction it goes right back in the box. I contact the seller and ship it out immediately.

    Sellers, for the most part, know what condition the item is in. I have yet to have a seller refuse a refund, and, generally speaking, they have refunded the initial shipping cost. I have seen some of these items right back at auction, with the same description as what I bought it under. Kind of a game...

    Sorry about the rant, Craig. For $75, it doesn't seem like you should have had to go through the "learning experience" for this particular lens, although you have my kudos for your excellent repair and follow-up on the forum. Good luck building your kit - don't tolerate junk, and don't forget to check prices with KEH before you bid up a particular item.

    Mike
  7. xo-whiplock
    xo-whiplock
    I agree. A learning experience all the way around.

    Craig
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