Lens Mount / Sensor Parallelism Inaccuracies Afflict All Brands
Related: digital sensor, focus skew, lens mount, lens mount / sensor parallelism, lens skew, quality control, Samuel Chia
See Update on Sony A7R IV Lens Mount / Sensor Parallelism.
I thought I would make darn sure that my recent posts on having a “swung” sensor in my Sony A7R IV should not be construed as implicating Sony as being unique with this issue—not at all.
Terminology: “tilt” is up/down and “swing” is left/right, and they overlap/combine in any camera. Rare is the camera with a sensor perfectly parallel to the lens mount.
Just to pick two major vendors:
- Three years ago, I had a brand-new “swung” Nikon D850; see Nikon D850: Testing for a Misaligned Sensor.
- This year, I now conclude that I had a slightly “swung” Hasselblad X1D because it made no sense to have several lenses all at fault for focusing closer on one side. See as one example Alabama Hills Formations, Late Dusk, which shows a left/right skew.
It’s tricky to distinguish lens mount / sensor parallelism from lens skew. It takes a ton of effort to be sure unless you already have “known good” gear (and really know that to be true).
Compounding matters, there is no perfect lens, only a continuum of poor to excellent (mostly good to pretty good), with each lens potentially having swing/tilt as well as other optical problems on top of baseline optical performance, field curvature, focus shift too. Some of these faults can make things worse or better in some areas of the frame, depending on the camera tilt/swing. The net result is often a head-scratcher.
In my experience, wide angle lenses show the issue much more prominently, at least when focused at relatively close range (up to 40 feet out). Focused farther away, it is easier to miss.
...
Thanks to Joseph Holmes (www.josephholmes.com) and Samuel Chia (cacaoeditions.com) for background information on their knowledge about swing and tilt in cameras and lenses through years of research.
Here is a good article on just how difficult it can be for demanding requirements, such as astrophotography:
... Many lenses have their plane of focus tilted by at least 50 microns or more, some even over 200 microns. That won’t be invisible in your photos. Not even expensive lenses are free of this problem. I’ve yet to find a single copy myself that has a tilt of less than 10 microns
... Recently, I acquired a Sony a7R IV and naturally, I tested it to see if the sensor is straight. It was tilted by some 10-15 microns and swung by about 30. That makes 5 out of 5 bad Sonys, if you are still counting...
My Sony CMOS sensor at the bayer CFA surface appears to be warped. I say ‘appears’ because we did not have enough time to make sufficient measurements to properly verify this. I was told by the Keyence representative that wafers and CMOS sensors he has measured have all been warped. He thinks that the warping usually doesn’t exceed 10 microns for camera sensors...
...measurements also revealed that the sensor cover glass was not perfectly parallel to the light-sensitive plane of the sensor. You can forget about making accurate contact measurement off the front side of the sensor
See also The Great Flange-to-Sensor Distance Article. Part II: Photo Cameras.
