The article has the answer to your question: There was no lens, just a pinhole. The lens and filter system gets integrated "over the next few months". They tested the sensor array, not the lens.

Ha, that's how I tested a DSLR that I had repaired. There was no matching objective there, so I wrapped aluminium foil over the front and, using a needle, stabbed a tiny hole into it. The pinhole setup was good enough to test what I needed to test :D

Funnily enough, the Airy discs from pinhole diffraction are perfectly resolved when zooming into the blurry romanesco.

I see, that's fair, though posting a big-zoom version is funny. I guess you can zoom in and see the dust particles.

As others have stated, there’s no lens for focusing.

What is however kind of surprising to me is the amount of hot pixels and also dust / debris on the sensors. You’d think that as expensive and fragile as they claim the sensor array is, they’d keep the environment cleaner. Example: https://www.dropbox.com/s/rhldlwyqzuvbf2o/2020-09-13%2007.36...

I also question the “five human hairs” wide gap between the sensor pods given that the gaps are clearly visible in the press photos of the sensor array.

None of the debris is on the sensors. There is some small amount of dust on a window, and it shows up twice as much due due to image processing performing bias subtraction.

The sensors are in a cryostat, and the effective size you of what you might thing as “dust” in these pictures would be quite large if they had been on the sensors (several mm)

Single human hairs can also be visible in photos.

> Single human hairs can also be visible in photos.

Not at the distance and resolution of a photo like this one:

https://www6.slac.stanford.edu/sites/www6.slac.stanford.edu/...

See the orangish lines between the sensors.

Those are pretty clear, though if they are significantly brighter than the sensors they would still be visible at a very fine width.

Those are cosmic rays

If you zoom into the picture (in the upper middle parts) there are a lot of transparent circles/torus shapes. I see exact same things (but didn't pay much attention to it) if I look into a bright light source and squint (especially if eyes are moist from tears). These circles also seem to move. What is it?

If they move, they are probably floaters (little cells or bits of debris floating around in your vitreous humor). In the image, they appear to be diffraction artifacts (airy function) from the pinhole aperture

A flat image was taken for bias subtraction and the debris shows up twice because the projector had moved slightly between images, so the image processing ended up subtracting where it didn’t need to and missing the original artifact.