A DIY Guide For Fixing The Rokinon/Samyang MFT Fisheye Focus Issue

The internet has quite a bit of reports that the Rokinon/Samyang/Walimex MFT Fisheye has some issues with its focus scale. The reports range from the annoying”Infinity is at the 0.5ft mark” all the way 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. (of course, this is all very informational, if you end up bricking your lens by following this guide, we are not taking any blame for it)

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).

Fix 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.

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

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 Loctite on the thread of the lens element. In case you do not have Loctite at hand, you can also use some nail polish. It basically works the same way. By using Loctite/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.

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

Before MTF fix

after MTF fix

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?

OLYMPUS DIGITAL CAMERA

Well, it still works. So: Happy Wife, Happy Live, (Happy Fisheye Owner) 😉

About The Author

Oliver Hanka is an enthusiast photographer from Munich, Germany. You can follow his work over at 500px profile.

Dan K

for a fisheye not to reach infinity (and right out of the box) quality control has to be pretty borked.
Addicted2light

Thanks, really interesting and pretty neat solution.

I have to point something out, though, for anyone else that should try this. Loctite is probably safe, as is nail polisher. But DO NOT use superglue, ever, near an optical element.

Cyanoacrylate (the main chemical component of superglue) will evaporate completely coating (and ruining, unless you like extreme soft focus effects) your lens!

It is the same stuff, btw, you see the CSI guys using to reveal prints on stuff once vaporized in a glass chamber.
Patrick Tollgren Lazarov

Use Loctite 242 (blue) for this. Loctite has 3 products for locking nuts/bolts (blue/green/red) and the blue is easy to unlock without to much force. http://www.loctiteproducts.com/p/t_lkr_blue/overview/Loctite-Threadlocker-Blue-242.htm
Paweł Duszyński

I was thinking about selling my lens because of this issue. Thank you so much!
Balazs Kiss

I have an old Samyang fisheye with a similar problem, tried to apply this fix previously, but unfortunately it was not a proper fix for me – when I unscrewed the rear lens element to have proper infinity focus in the middle of the frame, towards the edges it was still out of focus. Previously I was able to achieve sharp focus on the entire image. Tried to disassemble the lens as much as I could, but I had no luck figuring out what went wrong.
PaulC

Many of these manual chinese lenses have thin shims under the lens mount.

If you need to move the lens to mount distance, and there isn’t a screw (or screws) to do this on the lens barrell – undo the 3 to 4 screws that fix the mount to the lens, add or subtract shim and replace the screws. Thin plastic from youghut pots is easy to cut with scissors.