It is shocking what Google is doing with the Pixel 6 Pro. Multiple people already noticed that the Pixel 6 Pro often chooses digital zoom instead of the periscope camera. Here's an example that someone posted:
Pixel 6 Pro: camera app chooses digital zoom
Pixel 6 Pro: camera app chooses periscope camera
Version: HDR+ 1.0.403259735zd according to the exif data
The light conditions are not bad at all and the periscope image is much, much better. Also note that the periscope camera captures more
light per time from objects than the main camera (see below).
Google really needs to give us a setting that forces the periscope camera. This behaviour is ridiculous.
Other sample images from other people also strongly indicate that Google ignores the 50 megapixel or 48 megapixel mode of the sensors. This means that the 4.3x periscope camera is replaced with a 4.3x crop from the 12.5 megapixel mode, if the camera app refuses to use the periscope camera. This leads to an effective resolution of 12.5/4.3² = 0.68 megapixels
! This is also the reason why the maximum zoom setting of the Pixel 6 (not Pro) is only 7x (like the Pixel 3), it crops the sensor in its 12.5 megapixel mode.
Note that the periscope camera captures more than twice as much light
per time from distant objects
as the main camera (when you don't adjust the distance) because the effective diameter (entrance pupil diameter) is 19mm /3.5 = 5.43mm , whereas the main camera only has 3.68mm.
(Don't confuse the effective diameter with the f-number, which is related to light per time per unit area of the sensor. The Hubble telescope has a 57600mm f/24 objective.)
The only problem is read noise because the periscope camera delivers 17.5 times as many pixels per object as the main camera. This causes more read noise per object, but read noise is only relevant in low light conditions (for example completely dark room) or in very dark shadows. In decent light conditions, read noise isn't relevant and the periscope images would look less noisy
than a crop of the main camera sensor because the periscope camera captures more
light per time from an object than the main camera. Indeed, the periscope image isn't noisy at all.