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Adjusting manual (pulled back) focus on the Olympus 12mm f2?

Discussion in 'Native Lenses' started by quatchi, Jul 16, 2015.

  1. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    Hey,

    I have the wonderfull Olympus 12/f2.0 lens. It takes stunning and sharp pictures and I am quite happy with it. This was until I tried to do some night time astro shots. As it turned out, I am not able to focus to infinity when the focus ring is pulled back (i.e., manual focus is activated). When I turn the manual focus ring towards the infinity mark, 5 meters and beyond objects are still not in focus (at f2.0 - tested in daylight). Going past the infinity mark on the lens improves it a bit but objects still are not in focus. When the lens hits the physical stop of the focus ring, the focus plane is roughly about 3 to 4 meters away. The lens, however, is perfectly capable of focusing to infinity. When using AF or MF (set in camera with the focus ring NOT pulled back) I can focus without a problem.

    It seems, that the pulled back focus ring is completely off. As I learned on the net, the lens is never physically focused by the ring. Twisting the pulled back ring is only an input to the focus motor. Hence my question: Is there a way to adjust the input coming from the pulled back focus ring (e.g., through software)? Has anyone of you the same problem?

    Just for completness sake: I am using an E-M5. Also tried it with my Oly 12-40 and there everything works as expected, which means I can focus to infinity and beyond using the pulled back focus ring.

    Thanks in advance for any insights on this matter!
     
  2. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    You're probably going to have to send it in.
    Meanwhile, setting the camera to MF would let you focus using the ring without pulling it back... Does that work?

    Barry
     
  3. svenkarma

    svenkarma Mu-43 Top Veteran

    566
    Feb 5, 2013
    mark evans
    Same problem here, but as the GX7 has the MF/AF button on the back I just use that and don't bother with the clutch. I wasn't too fussed on the O17 one either, but it wasn't so wildly off.

    I probably should take it back to the shop as I've not had it long, but it's a bit of a trek.
     
  4. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    Mine does the opposite - infinity on the scale is focussed beyond it.
     
  5. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    This works. I, however, prefer the pull back mechanism for when it is dark (astro photography). I wrote Olympus an email. So far no response - I will keep you updated.
     
  6. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    A first short feedback: Olympis sayed that they are not aware of this issue and I should send the lens in.
     
  7. c0ldc0ne

    c0ldc0ne Mu-43 Regular

    71
    Oct 9, 2012
    You could have been the umpteenth customer calling in with exactly the same issue that day, and they still would have told you that they're not aware of it.

    Damage control always trumps customer satisfaction for big corporations.
     
  8. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    I promised you some feedback on this issue:

    I had my lens send in to Olympus. It took two weeks and I got it back. There was no letter or anything stating what they have done. The only clue that they had it in their hands was an additional plastic wrapping of the lens. So I checked it out and... you probably guessed it already: nothing has changed. The lens still has the same issue. So I called customer support again. First they said it is next to impossible that there was no note explaining what has been done. After I promised that there is really, really (once more: REALLY!) no note, the guy on the hotline checked the records (which took a while) and came back with: "Well, they serviced the lens. They greased the focus ring and cleaned the lens. So, every thing is fine". It took me a while to explain to him that nothing is fine and that the problem is in fact not fixed. It was then that he finally read the initial fault report - probably only now understanding the problem with the lens. The result was: "I guess you have to send it in." I will spare you here the rest of the conversation where we debated who has to pay for the parcel...

    So, to wrap it up: The lens is going back to Olympus again. This time with an additional sheet of paper with drawings and text explaining the issue in more detail. Needless to say, so far I am not overly impressed with the Olympus service...


    On the plus side, though, I can show you a diagram explaining the problem which might also enlighten/entertain the Olympus service team. :)
     

    Attached Files:

  9. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    Interesting, it sounds like the potentiometer used to detect position isn't aligned correctly or has a short causing the higher values to not register (thus only focusing half way).

    Certainly not something I've ever heard of, as previously mentioned in this thread normally it focuses well past infinity on the pull back.
     
    • Informative Informative x 1
  10. bassman

    bassman Mu-43 Top Veteran

    680
    Apr 22, 2013
    New Jersey
    Scott
    Just tested my 17/1.8 and the ring seems to work fine when pulled back. But it works without pulling it back if I have MF on, so I don't see the point.
     
  11. b_rubenstein

    b_rubenstein Mu-43 All-Pro

    Mar 20, 2012
    Melbourne, FL
    Typically a digital position encoder is used for focus distance information in the lens. Focus distance information is used for multiple functions in the cameras and has to be digitized for processing. It's also environmentally more robust and can be fabricated on a flexible substrate that can be wrapped around an internal lens barrel.
     
    • Informative Informative x 1
  12. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    It's all well and good saying that however they use what is basically a potentiometer with a 10 bit AD in practice, it's two strips of resistance wire which wrap around the barrel with a bit of sliding wire running along it which shorts it, voltage is passed through it and depending on the position the AD converter reads a voltage and that's converted into a distance (say 980 for infinity, 1024 is end of range however the last few values at either end are not used as it will never reach them in practice).

    It's the same system they use on many focal length detection systems for zoom lenses however rather than breaking the range up into 3-4 zones for greater granularity it's only one strip for the full range.

    Digital position encoders are used for the lens positions as they are far more accurate, however generally they're annoying to work with as they die very easily (touch one, I dare you).
     
    • Informative Informative x 1
  13. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    The point is very easily explained: Astrophotography. The usual MF is without any physical stop/feedback. So you turn and turn the ring without knowing the lens' actual focusing position. If the stars are bright enough, you can use the magnification to focus properly. In case the stars are to dim, however, you are lost. That's when a MF ring with markings on the lens comes in handy. You know at what distance the lens is focused at for each position of the focus ring (at least in theory - not on my lens evidentially).
     
  14. bassman

    bassman Mu-43 Top Veteran

    680
    Apr 22, 2013
    New Jersey
    Scott
    Good point!
     
  15. tradesmith45

    tradesmith45 Mu-43 All-Pro

    Dec 13, 2012
    Oregon
    Hey quatchi hope the 2nd time does the trick. Here's a little info from my testing. I do lots of night landscape shooting w/ the M.Z 12mm & other lenses on my E-M5.

    First, the EVF on the EM5 is pretty poor (compared to my EM1) for the task of focusing on a dim star at night even using mag view. Have a similar problem using adapted ultra-tele too. That's why I bought the M1. I'll eventually sell the E-M5 for something w/ a better EVF & hi ISO performance but right now the M5 sensor is IMHO the champ for m43 astro.

    As for the M.Z 12mm, I've tested where infinity focus is during daylight w/ the focus ring pulled back. On mine, its half way between the 3m & 5ft marks. But the surprise to me was how course the focus steps are (its still focus by wire using the AF stepper motor). There was only 1 position where the lens gave sharp infinity focus & the steps on either side of this position were out of focus (@14x mag view). The M.Z 12-40 Pro & M.Z 17mm f1.8 are both a bit less sensitive. Combine this sensitivity w/ the poor M5 EVF & doing this at night is really tough. I certainly got slightly out of focus night shots when I first started. I'm more careful as a result. I'll sometimes refocus just for the hell of it.

    In the old mechanical focus days, we'd say the 12mm has a very short focus throw.
     
    Last edited: Sep 30, 2015
    • Informative Informative x 2
  16. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    tradesmith45: thanks for your response! I tried with my 12mm and went through the whole range slowly. I goes smoothly from close focus to like 2-3m until it hits the physical barrier. Thinking of it now, I should have made a video also for the Olympus guys. :) I tested the same with my Oly 12-40mm and with this lens everything is fine. I even can focus past infinity (or so I guess) with the pulled back focus ring.

    What I find interesting is that your lens is at infinity at around the 3m & 5ft marking and not at the infinity marking either. It seems like there is no consistent manufacturing process - which again might hint that eteless is right with a "cheap" sliding potentiometer.
     
  17. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    The linear potentiometer route might be the cheap option however it's also normally reliable in mass production, the lens doesn't need to remember the rings current position so it cannot get 'lost'.

    Using a linear encoder of some sort would be more accurate however it's also a far more complex system with far more points of failure (such as dirt/dust), the most basic form of this would be photo interrupter like in a mouse wheel or anti lock brakes (which can sense rotation and speed of rotation very well) however all of these methods have the same problem in that they have no idea *where* in the rotation the focus clutch would be, if the basic resistive circuit is working correctly it's always a straight read to get the correct location.

    While it might not be as precise as other methods there are far less points of failure (It's easy to design, compact, cheap, and has a long service life), I'm happy to give up a small amount of accuracy for all of the advantages offered.
     
    • Appreciate Appreciate x 1
  18. tradesmith45

    tradesmith45 Mu-43 All-Pro

    Dec 13, 2012
    Oregon
    FWIW my M.Z 17mm f1.8 reaches infinity focus when the focus mark is just on the left edge of the infinity symbol. So it can focus past infinity like all AF/MF lenses I've ever seen. Since moving to digital 3 yrs ago, I never expect infinity marks to be useful.

    In fact my Kowa 8.5mm MF lens is worse than the AF lenses. It hits infinity at the 5' mark!
     
    • Appreciate Appreciate x 1
  19. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany

    In your signature I read that you have the E-M1 and E-M5. Is there a difference between those two cameras? As you also have the 12mm: Can you do me a favor and check with the lens whether there is a difference between those to cameras? Thanks already!

    I had my lens for two times at the Olympus service by now and the problem is still not solved. The second time the lens was returned the "repair report" stated that everything is in range with the Olympus specs and parameters. As I can not believe that the Oly specs are so far off, it came to my mind that it might be an issue with the camera itself (also performing a hard reset didn't change anything). Unfortunately I do not have a second u43 body at hand to test it myself.

    Another "side question": How does the focus clutch mechanism work internally. When I turn the clutch (not retracted), I believe that the signal is transmitted to the camera which in turn then sends a signal to the lens' focus driver*. How about the retracted clutch? It is "focus-by-wire" as well, but with the camera in between or driving the focus mechanism directly?

    ---
    *) At least it appears that way because you can change the turn direction of the focus ring in camera.