Sony FE 35mm F1.4 ZA teardown
 |
We’ve already looked at Roger Cicala’s teardown of the Canon EF 35mm F1.4L II, where he showed it to be a heavy duty design with extensive adjustability to bring it back to spec after a period of abuse. LensRental’s look inside the Sony FE 35mm F1.4 turned up a lens designed with a radically different approach. It’s easy to over-interpret the differences and start trying to picture the different use-cases they’ve been designed for, but even if you don’t want to extrapolate so far, it’s fascinating to see how unconventional Sony’s approach is.
Read Roger’s full article for a piece-by-piece teardown as well as his thoughts on Sony innovation and design
Taking a more linear route
 |
The most fundamental difference Cicala highlights between the two designs is how the focus elements are moved. The Canon uses a traditional helicoid design – rotating the focus element along a helical track, in much the same way as manual focus lenses would. The Sony design instead uses a piezoelectric drive to push and pull the lens element along a rail, meaning that there’s no rotational movement occurring at all. Instead it can be shuffled back and forth in very fine increments.
Sony calls this design ‘Direct Drive SSM’ (with SSM standing for Supersonic motor), and it’s based on technology used for in-body image stabilization in Sony A-mount cameras, hinting at the speed and precision that such systems can provide. It’s distinctly different from the linear motor technology used in the FE 55mm F1.8, which you can see in operation here.
Direct drive SSM
 |
The Piezoelectric drive mechanism is fascinating, and we saw it embedded in a cut-in-half FE 35mm at CP+ last year. It involves a drive element that can be expanded or contracted by applying an electric current. Expanding it slowly moves the lens out along its mounting rail, but the connection to the rail is designed to slide in response to rapid movement, so rapidly contracting the drive element leaves the lens in the more distant position but with the drive element retracted. Repeating this pattern of slow extension and rapid contraction progressively nudges the lens away from the drive element. Pulling the lens back again involves reversing the process: rapidly expanding the drive element so that it slips through the clamp, then slowing drawing the lens back in, one step at a time.
Why do it this way? Well, it’d certainly be quiet and it allows very fast movement, giving the lens possibly the fastest focusing we’ve ever seen in this class: when paired with the a7R II’s phase-detect AF system, autofocus is quick and precise. A single element able to move quickly back and forth in tiny steps lends itself well both to contrast detection focus in video as well as being able to reverse directions when subjects erratically switch between approaching and receding.
Adding a snap to aperture-by-wire
 |
Another interesting design detail is the switch for engaging and disengaging the stepped, clicking aperture. A weather-sealed switch pushes a small, sprung ball bearing against a series of tiny teeth, to give tactile feedback as you rotate the aperture ring. However, no other mechanical connection is engaged: the aperture is entirely controlled by-wire, with a sensor detecting movement of the aperture ring and relaying it to the aperture motor.
Locked on place
 |
The other major difference between the Canon and the Sony is the philosophy behind lens alignment. Where the Canon had a series of shims and adjustment screws to allow the different elements to be re-aligned, and re-centered, the Sony has most of its elements glued together in one giant module. This whole module then has three shims offering only a small degree of adjustment. LensRentals’ testing of its copies suggests this adjustment isn’t sufficient to give the consistency you might hope for.
Individual replacement parts are not available for after-market repair: the only option is to slot a whole new module in, with limited adjustment to ensure its alignment within the lens barrel. This approach means Sony has a good level of control over the alignment within each module but means the lens is harder and more expensive to service if it goes out of alignment or if the front element gets scratched.
In summary
 |
The construction and adjustment isn’t quite as extensive as in the Canon but, as Cicala highlights: nor is it in most lenses. Instead it appears Sony has designed its lens so that it’s durable and everything is fixed in place, whereas Canon has built its lens to be tough but accepted that as a photojournalist’s workhorse, it’ll need to be beaten back into shape every now and again.
it’s clear, though, that Sony has built this lens to be tough: not only is each element individually positioned, rather than being spaced apart, relative to another, but Sony has included extensive amounts of weather sealing at every step of the design (just look at the size of the rubber gaskets, in the picture above). Cicala concludes: ‘This lens has the most rubber gaskets I’ve ever seen. The weather and dust resistance in the lens itself should be superb.’
Read Roger’s full article for a piece-by-piece teardown as well as his thoughts on Sony innovation and design
Articles: Digital Photography Review (dpreview.com)