Sony FE 35mm 1.4ZA focus repair and weridnesses

Variations in the final product are nothing unusual. In mass production, reliability gets refined, costs are optimized (though sometimes one comes at the expense of the other), and engineers make small tweaks to the design along the way. I can name several pieces of photographic gear where identical external appearance hides very different internals. But this time, Sony has outdone everyone — two completely different lenses hiding under the exact same nameplate!

That’s a bit of a spoiler, of course - I only reached this surprising conclusion after fully tearing the lens down for repair, screw by screw. Before that, I was absolutely certain I was about to face the same kind of job as in my earlier post about the Zeiss 50mm 1.4 ZA. I had seen a colleague's video clearly showing a regular ring-type AF motor inside. But - let's start at the beginning.

The Distagon T* FE 35mm F1.4 ZA arrived with a "camera doesn't recognize the lens" complaint, although it did show some signs of life - the aperture would open and close when mounted. For modern lenses with fully electronically controlled focus and aperture (true for Sony and many others, but not for old EOS, for example), the camera runs a quick self-test at startup. It checks the focus mechanism, the aperture, and - if present - the optical stabilizer. The focusing group moves to near-infinity, the aperture first fully closes then fully opens, and the stabilizer lens moves to the center position. If any of these tests fail, the camera refuses to recognize the lens.

It's not a very fair to customer - if the focus motor fails, you can't even use the lens manually. But that's how modern designs work: with no direct mechanical connection between the focus ring and the optics, manufacturers see no point in leaving partial functionality.

Knowing this lens has no optical stabilizer and that the aperture was behaving normally, I went straight to the focus motor, expecting to find a seized ring-type motor.

Like most modern Sony lenses, you can't reach the internals without taking it apart from both ends. Starting from the front, the decorative nameplate - firmly glued in place - hides the screws for the filter-thread mount:

The front group has to come out to access the motor. That means securing the factory shims with a drop of glue - Sony was generous with them here.

This front group is factory-centered and fixed with adhesive. Removing a centered element is always risky - without realignment, you may never get the same optical quality back. Even worse, there was no way to check sharpness beforehand: the lens failed initialization, and the focus position was unknown.

Spoiler: the centering here doesn't critically affect sharpness across the frame, and reinstalling it by matching the old glue marks works fine. Just remember to mark its position, since it can be installed in three different orientations.

The group comes out - and here's my first real surprise: this lens isn't built like the one in that video.

Suspicious, but the teardown must go on. Moving to the back: Four bayonet screws to get to the PCB. But here's a twist: the shims are arranged in a rather unusual pattern. You'll want to note their exact order for reassembly; gluing won't help you here.

And then - another surprise. That little rectangle I'm pointing to with tweezers says it all: this isn't a ring motor at all, but a miniature linear ultrasonic motor - the DDSWM type. Suddenly the odd behavior makes sense. These motors are fragile, and when they fail, focusing stops entirely.

To go further, part of the barrel needs to be removed. After undoing four screws, you simply lift it slightly, remove the mode switch, and slide off the barrel ring:

The aperture comes next - two marked screws hold it in place. Disconnect the flex cable and carefully feed it through as you remove the unit.

Next up is a bit of a mystery - a weight plate? The rubber supports for the focus motor press against it, but the motor itself is firmly screwed down.

Three screws secure the focusing module:

It's also held by the motor's soldered wires and a position sensor. Remove the sensor and desolder the motor. The sensor, by the way, is a non-contact magnetic type:

Here's the module itself:

From here on, it's easier to show than to explain - see the video below. In short, these motors are repairable in about 50–70% of cases, and this time, I got lucky.

During reassembly, don't forget to hold the metal guide rod on the focus module:

The rest went smoothly, and after putting everything back together I confirmed the motor was working and sharpness met my (very strict) expectations.

Definitely a win.

As a bonus - two identical name rings from two completely different lenses:

Here's to getting spectacular shots with great gear!

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