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[DIY] Fixing the Rokino/Samyang/Walimex 7.5 MFT Fisheye Focus Issue

Discussion in 'Native Lenses' started by quatchi, Nov 21, 2015.

  1. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    The internet is full of reports that the Rokino/Samyang/Walimex MFT Fisheye has some issues with its focus scale. The reports range from "Infinity is at the 0.5ft mark" up to "not focusing to infinity at all". My lens had the latter issue. That's why I started to look around the net for a solution. Unfortunately I couldn't find a real tip on how to fix it. The only hint I got was from the rear lens element becoming loose on some lenses.

    In fact, the rear lens element was also the issue of my not focusing to infinity problem. I was able to fix it by unscrewing it a bit. Here is a DIY guide on how to fix your lens in case you have focus issues as well.

    The issue:
    The rear lens element is not properly aligned. This means, in case your lens focuses past infinity, the lens element sticks out to far (= probably to much unscrewed). In case you can not focus to infinity at all, it means the rear lens element does not stick out far enough (= you have to unscrew it a bit).

    DIY guide:
    First of all, test your lens (at f3.5) and figure out what exactly is your problem (infinity to early or no infinity focusing). Then dial the focus ring as far as possible towards infinity. This means, the rear lens element (red arrow) is coming out as far as possible.

    IMG_1171.JPG

    Next, unscrew the three screws (blue arrows) and remove the bayonet-housing (silver).

    IMG_1173.JPG

    Afterwards you can tighten or untighten the rear lens element (by screwing it).

    Site note: In case you want to clean your aperture blades, simply unscrew the lens element completely.

    The next steps are a bit of trial-and-error. Tighten/untighten the rear lens element a bit, put the bayonet-housing back on (fix it at least with one of the screws) and mount the lens on your camera. Use the focus magnification to determine whether your lens now focuses correctly or not. Repeat the steps a couple of times until you nailed it... :)

    In my case, the rear lens element was screwed in completely (and quite tightly) and I had to unscrew it for more than 1.5 turns. So, just experiment a bit.

    After you found the correct rear lens position for your lens, take off the bayonet-housing for a last time. In order for the rear lens element to stay in please (after you adjusted it so carefully for the last hour.. :) ), put some Lock-Tide on the thread of the lens element. In case you do not have Lock-Tide at hand, you can also use some nail polish. It basically works the same way. By using Lock-Tide/other brand/nail polish, the lens element gets stuck and should not come loose by itself. The upside compared to superglue is that with a bit of force you can still unscrew the lens element.

    IMG_1174.JPG

    That's it. Here is a before and after 100% center crop from my lens.

    PB212514.JPG
    PB212529.JPG

    As you can see, before the fix, the lens' focus plane was on the curtain (focus ring slightly past infinity). After the fix the trees are also in focus.

    And how about close focus after the fix?
    Well, it still works. So: Happy Wife, Happy Life, (Happy Fisheye Owner) ;-)

    PB212528.JPG

    Article at DIYphotography.net
     
    Last edited: Nov 23, 2015
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  2. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    It has a floating rear element by design for close focus correction (it's not a unit focusing lens), almost all floating element designs are designed to focus past infinity as mount tolerances would cause it to miss infinity otherwise. It's a 7.5mm and any tolerance issues with the mount will result in it missing the infinity stop on one camera while being perfect on another, mass production precludes perfection.
     
  3. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    Thank you for that. Mine ever so slightly focuses short of infinity, but stopping down a little fixes it. However, I may take the trouble to fix it.
     
  4. aidanw

    aidanw Mu-43 Regular

    116
    Nov 19, 2012
    Wellington, NZ
    My Samyang 7.5mm varies depending on the camera. Infinity focus is a finger's width before the infinity mark on my E-M5, but on my partner's E-PM2 the infinity mark is exactly where infinity focus is.
     
    • Agree Agree x 1
  5. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    I just checked on two E-M1 bodies (one is 2.5 years old, the other around a year and a half), there's a 1mm difference between them on the focusing ring. Not as much however it would mean adjustment for one would mean not for the other. I suspect given the short focal length that temperature of the camera and lens would also make a difference as to the point at which infinity is reached due to thermal expansion of the metal construction.
     
  6. Klorenzo

    Klorenzo Mu-43 All-Pro

    Mar 10, 2014
    Lorenzo
    Do you think you can turn the ring with a rubber ring-like item without removing the bayonet part? Could make the process a little faster.
     
  7. quatchi

    quatchi Mu-43 Veteran

    326
    May 17, 2012
    Munich, Germany
    It might work. It depends on the current "condition" of the lens element. Mine, for example, was screwed in tight and I couldn't loosen it without removing the bayonet-housing.