The photographic hire company Lensrentals had a $2k Sony FE 135mm f1.8 GM camera lens returned with a problem: it was having issues focusing. So, they decided to do the obvious thing and take it apart. It’s a fascinating insight into some of the engineering that goes into a high-end camera lens.

That is perhaps a rather scary thing to do, because this is a very new lens that doesn’t even have a service manual yet. That’s akin to rechipping a Ferrari when you’ve never even opened the hood before.

One of the interesting things inside is the presence of a number of shims that adjust the placement between the groups of lens elements. It seems that however good their manufacturing tolerances are, sometimes you just have to put a shim or two in there to align things.

There is also a tantalizing glimpse of the focus mechanism, which slides one of the element groups back and forwards to focus the lens. And again, there are some manual adjustments that are made with screws to keep this group of lens elements aligned.

Unfortunately, Lensrentals didn’t go all-in with the teardown: they stopped when they found the problem, in which a single element had shifted, throwing off the performance of the entire lens. That’s a pity, as camera lenses are a major driver of miniature electric motor innovation, needing as they do to move large groups of elements quickly and very accurately to focus. There is an excellent view of the aperture element though, and it is possible to see how the lens uses twelve metal leaves to create an almost perfectly circular aperture.

This article is well worth a read if you would rather not tear apart your own expensive camera lenses.