Disassembly – 7Artisans 50mm F1.8 lens

It took a lot of time to understand how to disassemble 7Artisans 50mm F1.8 lens. It was one of the most challenging puzzle for me. Many times I was thinking about simply cutting lens in half to understand how to approach it : ) Finally the riddle is solved and this article shows the steps.

Discovery notes

Biggest stopper of 7Artisans 50mm F1.8 disassembly is the absence of screws on the surface. Yes it has three bolts on the mount ring, but once you remove it – you are stuck. Tot a single bolt or any hint from lens look what to do next.

I had to make exploratory drilling of lens areas to better understand how the internal mechanics is organized : ) That drilling doesn’t affect lens performance after all, though makes it less attractive. But that is fair price to pay for solving the 7Artisans 50mm F1.8 mystery without ruining this excellent lens. So ignore all drilled holes on image samples. They are not needed for disassembly.

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First success happened when I drilled few holes in a nameplate ring and was able to rotate it CCW using spanner wrench. It allows to get access to all front glass elements at front of aperture. Though later I understood that it is not needed actually, so don’t do it – the glue holding that nameplate thread is quite strong anyway. Anyway, it helped to discover more about lens (and safely drill few new holes).

Disassembly steps

First step of 7Artisans 50mm F1.8 lens – is to unscrew whole front frame block CCW. It’s not easy to do because factory glue is very strong. However knowing that doing so does not ruin helicoid or focusing mechanics is good (I was afraid to use extra power in past, thinking it may damage focusing). To do this operation safe, set aperture ring to F1.8 first (if you set it to F16 like I mistakenly did, torque power will break aperture transmission bolt). Then put rubber bands – one on top of front frame, another on top of mount ring and frame near it. Significant power is required to break the thread glue. Make sure aperture ring remains in F1.8 position. After front frame starts to move. lay the lens down on table and unscrew frame. If you tilt lens – all glass will fall out, so keep it like on picture. As you can see the thread is thin and wide.

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I’m showing that nameplate can be also unscrewed. You can do it after removing front frame, which is safer to do.

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Now keep in mind that glass is laying down in front module, so carefully pull that module by holding outer fame areas. Do not tilt it.

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Now you can see the aperture.

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Use spanning wrench to unscrew CCW thin ring holding the focusing ring.

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Then rotate focusing ring CCW and pull it out. You can see that there are two guiding bolts for focusing ring threads, which are moving rear lens core module when focusing.

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Remove ring with DOF scale by unscrewing it CCW. It may sit quite tight, so make sure you don’t rotate aperture ring from it’s F1.8 position.

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Then remove aperture ring. The aperture transmission bolt on picture is my replacement to the broken one. You will see much better looking brass bolt.

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At this point you can unscrew aperture transmission bolt, and also two helicoid guiding bolts and pull out rear lens module.

Conclusions

The reason for disassembly may be to clean any internal dirt, or try to fix focus ring threads (at the end it may get distorted over time, and can be fixed for more smooth focus by folding ending edges slightly inward). There are no easy way to calibrate infinity focus on this lens other than adding some shims between mount ring and lens frame. Also I had a chance to disassemble aperture module (it’s integrated with rear lens module), the complexity of mechanics is impressive when you think about relatively low price of this lens.

The reason 7Artisans factory are gluing front frame thread is – if it’s not secured, simple removing of stuck front filter would cause front frame to rotate and shifting front glass. Potentially small side screws could be used instead of glue, but that would make production more expensive. Personally I’m not going to secure it with glue again, instead I’ll create small thread on the side and use securing bolt. However once tightened the front frame remains in place, so it may work that way as well.

Image samples on X-T30

I’ve took lens for a walk after re-assembly. If you don’t touch the glass lens optical performance will not be affected. It’s sharp in the center at F1.8.

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and 100% crop from above

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7Artisans 50mm F1.8 is an inexpensive, lightweight and little lens I enjoy a lot. It has decent sharpness and now I also know how to repair it if needed : )

8 comments

  1. I just received this lens from amzn and it’s decentered as usual with 7artisans. I just unscrewed the back, removed the 2 little lenses and reassembled. Now the lens is much better even if not perfect. Thanks for giving us courage! 😉

    Liked by 1 person

      • I have a question 😉 I just received a Pergear 25mm f/1.8 from amzn. It has a huge play in the inner barrel and everything goes out of focus when pushing slightly the front element. I disassembled it from the rear but I cannot find anything to reduce the play. Do I just return it or you have a simple fix? Thanks!

        Liked by 1 person

        • It sounds like the first version of 7Artisans 50m F1.8 I had before, with same noticeable play of the barrel. Surprisingly the second sample didn’t have that play at all. So I think it’s good idea just to return the lens and try another sample. Regarding the potential fix, it may help to add extra grease around inner barrel to reduce play, but may not completely solve the problem.

          Like

          • OK, so it’s a matter of large machining tolerances of the barrel, not just something one can tighten. I can see the same phenomenon on the Pergear 35mm I told you about before, but the amount of play is much less. In comparison, the 7artisans 35mm f/1.2 and the (new) 50mm f/1.8 are mechanically jewels… Thanks anyway!

            Like

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