I still didn't get any useful results with this shield. I put it away for a while, but recently the camera support for CircuitPython was rewritten, so I though I will try again. All I managed to get is some damaged JPEG frames:

But that suggests, that indeed both the hardware and software do work and all the connections are correct, there is just a problem with reliability. So maybe some of those capacitors, resistors and inductors that are on those example schematics, that I completely ignored while designing my shield are actually necessary?

You can see there are quite a lot of them, and I reduced it all to just two, because I didn't want to feed the Big Capacitor consortium that puts all those unnecessary capacitors on the schematics. Well, easy enough to test, what if I put back some additional caps and see if that affects the reliability?

By the way, someone should really start to produce parts that contain several capacitors in parallel inside them, so that you don't have to do things like this. Anyways, I added two 220nF caps to those 1µF caps I already had there, to see if it would change anything. And yes, it does! Now my code crashes into a hard fault handler instead of outputting corrupted JPEGs unreliably. Which seems like a worse outcome, but the important part is that there indeed was a change, so the filtering actually has an observable effect.

So the next step is to redesign this camera shield with the full complement of capacitors and other filtering paraphernalia, and see if that works. If it does, *then* I can see if some of them can be removed.