IBIS Fractures ? Is that a thing ?

Started 3 months ago | Discussions thread
Antisthenes Regular Member • Posts: 364
Re: Not really an issue for most users, IMHO
1

57even wrote:

Antisthenes wrote:

It's thus pure speculation of my part that twisting torque between the body shell and the lens mount caused by, say, human muscles might be involved, but it's not entirely illogical to consider, when trying to determine what might cause a linkage element to fracture, the origins and respective magnitudes of the forces that might be exerted on said elements.

For one thing, anyone twisting a lens hard enough to distort the body would almost certainly damage the lens mount and cause other issues, but that was not stated as a co-factor. In fact, fewer had mount issues than IBIS fractures.

The magnitude of the body flex induced e.g. by excessively muscular torsional forces doesn't have to be huge.

Let's compare the pictures from

https://www.lensrentals.com/blog/2020/06/the-great-flange-to-sensor-distance-article-part-ii-photo-cameras/

and the pictures from a Sony A7R2 teardown by iFixit.com:

https://www.ifixit.com/Teardown/Sony+a7R+II+Teardown/45597

A comparison with the known size of the active area of a "full-frame" image sensor — about 24x36mm — shows that the fractured positioning pin (indicated by a yellow arrow) protruding from the mobile support frame, presumably made of magnesium alloy, must have a diameter of circa 1.1 millimeters.

The lateral displacement of that fractured pin and of the frame-holding screw next to it, seems to be a fraction of a diameter of said fractured pin — i.e. a fraction of 1.1mm. We're talking maybe a 0.5mm lateral displacement, which isn't huge, and seems within range of the amplitude of a possible body flex.

The fractured (magnesium?) pin has a diameter of ca. 1mm, and hasn't moved very much laterally

Secondly, if you'd bothered to read further...

https://www.lensrentals.com/blog/2020/06/the-great-flange-to-sensor-distance-article-part-ii-photo-cameras/

You'd see that the fractured component was a plastic plate to which the sensor is mounted, which I would interpret to mean that it's part of the floating assembly, not the one mounted to the body.

Someone forcibly trying to twist a lens in the wrong direction will probably apply both a torsional shear force, and a compressive force on the body, as a natural tendency is to try to press a lens into the body when trying to rotate it forcefully.

If the twisting and compressive forces are sufficient, then, maybe the camera body will flex a bit.

These pictures show how little mechanical clearance exists between the floating assembly and the shutter frame that is fixed to the body shell:

Very little mechanical clearance between the black "floating" frame and the greenish, fixed shutter frame

Very little mechanical clearance between the black "floating" frame and the greenish, fixed shutter frame. The screw head has a diameter of about 3mm, indicating the screw has backed out about 0.5mm

Since there's so little mechanical clearance between the floating assembly and the shutter frame, it's not impossible that twisting and pressure could be communicated to the floating assembly via the shutter frame if the body flexes enough.

Note that, from a torsional and lateral movement perspectives, the floating frame's freedom of movement will, ultimately, be restricted by the stops built into the strong L-shaped steel brackets holding the permanent magnets. After the floating frame reaches these stops, it might then be subject to the full twisting and pressure constraints communicated to it, say, via the fairly thick optical stack being locked into the fixed shutter opening gate. A twisting / flexing of the shutter opening gate might thus interact, mechanically, directly on the optical stack.

The optical stack protrudes significantly above the screw heads, and we already know that the mechanical clearance between said screw heads and the fixed shutter frame is quite limited. It's thus not impossible, IMHO, that the optical stack might get "locked" into the gate of the fixed shutter frame and get twisted with it.

The fractures of the black plastic floating frame near the holding screws, and the popped off retaining clip observed by LensRentals, are consistent, IMHO, with said frame having been subjected tocompression and / or twisting.

Fracture of the floating frame near mounting screw, and popped-off clop are consistent with significant pressure and twisting constraints being applied to said floating frame.

Personally, I have some doubts about the rigidity of the A7 series' body shell and its ability to resist an energetic, muscular torsion and pressure without any deformation.

Besides, observing the sensor being moved by the IBIS during a long exposure of, say, 10 seconds, the observation of the movement being thankfully made easier by the minute dust particles sitting on the sensor glass which I should probably clean, show that the movements are quite slow. I doubt that such movements would yield enough acceleration to subject the floating frame to such mechanical constraints as would cause fractures of the plastic frame or of magnesium pins, or have enough force to pop a retaining clip.

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