I can’t find the explanation so I’ll give you a brief summary from my defective recollection.
I’m sure 50% will be incorrect so, I’ll illuminate the Bat Signal, and
@Nigel can fill in the blanks.
I always knew something was fishy with manufacturer claimed FOV specifications.
I became obsessed with measuring / verifying listed FOV specifications when I saw how easy it was to read a telephone number on a propane truck when I was testing the;
A139 Pro IMX678 (2023) specification 140° / measured 111°
A229 Duo IMX335 (2022) specification 140° / measured ???°
A119 Mini 2 IMX675 (2023) specification 140° / measured 99° (original lens)
A119 Mini IMX335 (2022) specification 140° / measured 93°
All four cameras have the same 140° listed specification, but provide different recorded footage FOV’s.
Ever since then I’ve always wanted a Viofo 4K model with the “narrow” 93° lens from the original A119 Mini (2022), but’s it’s not possible, (more on that later).
A bit later is when I started the “VIOFO Horizontal FOV Database” to measure / document all past & future cameras.
Now that I had evidence documented I was able to get an ex[planation from Viofo.
Q: Why do all your cameras have the same 140° FOV listed specification, but each camera provides a different FOV on the recorded footage?
A: Keep on mind I’m paraphrasing;
Dash cam manufacturers do not make lenses.
They simply buy them from a vendor (lens manufacturer).
The lens manufacturer provides a specification for each lens to the dash cam manufacturer.
The dash cam manufacturer uses this provided specification for their camera specifications.
However, once the lens is mounted to an image sensor, and the image sensor / lens assembly is installed in a camera housing the final assembled FOV is different.
Also, the same lens mounted on different image sensors will produce different FOV’s.
Once the camera is a final assembled product, my common sense would suggest dash cam manufacturers would check lens focus & assembled lens FOV as part of R&D, and Quality Control.