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Lens internal parts

A few mechanical elements used in Sigma lenses (image courtesy of Sigma Japan).

Tawainese repair center NRC has documented the repair of a water-damaged a Sigma 35mm f/1.4 Art, with pictures and comments on its internal design.

The lens had at least one glass element covered with droplets after a fall into water. Disassembly revealed that moisture had in fact taken its toll on many other inner parts.

So here are NRC’s findings:

  • The main holding tube is almost completely metal made. The outer shell is plastic (it may actually be Sigma’s Thermally Stable Composite), and acts as a damper when a hit occurs.
  • The autofocus (HSM) motor is surprisingly large – much larger than that of the Nikon 35mm f/1.4G, for instance. The location of the AF motor’s bearing reduces the risk of having it jammed or damaged by dust or water (water can leave mineral deposits, so hiding/sheltering the most sensitive parts is important).
  • There is rust on the motor’s shell. However, the stator was not affected, and it’s not by luck: Sigma shielded it with a sheet of copper that itself doesn’t rust, and doesn’t affect conductivity. There is a comparison with what Nikon uses in their pro lenses, but all three translations I could get are not clear enough, so I won’t say anything about it. What is clear though is that Sigma’s solution is very good in terms of durability.
  • The motherboard is well designed and integrated.

Is there anything to improve? The tightness of a certain group (of lenses?) could have been better, and the screw fixing agent apparently needs to be more resistant against dissolution. Don’t take my word for that – translations are a bit sloppy for this part as well. In any case, this is nothing to worry about.

It’s always reassuring to feel that a lens is well built, but we consumers only see the tip of the iceberg. Internal parts and assembly tell the story when it comes to reliability.

Global Vision lenses have been on the market for a bit more than 2 years (as this is written), so long-term durability is unknown. But from what we can see in this report, they should last long and stay in good condition over the years.

[Source: [NRC] 深度解剖 Sigma 35mm F1.4 見證外星人的科技, on Photoblog.hk]

Thanks to the reader who pointed out this article to me.

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