Okay, here are some results from a nearly new, unmodified NIkon Z50 II camera and a Voigtlander 50mm APO lens at f/2.8. I used an ISO of 1600, an exposure of 1.6 seconds, and a blank-screen iPad (dark gray TIFF image) with a sheet of flashed opal glass between the iPad and the camera lens (I also used several sheets of white paper stacked flat between the flashed opal glass and the iPad). The results are from a master flat that included 48 flat frames and 64 darks. I rotated the camera after every 8 flat frames so any non-radial variation in the iPad's display should have been reduced (mostly, if any existed). I used PixInsight for the calibration and flat integration and then PixelMath to produce the red divided by green and blue divided by green output images (from the debayered and channel separated master flat).
IMO, these results will vary with the exposure level, ISO, vignetting, and level of stretch applied to the resultant images but I think my copy of the Z50 II really isn't showing much in terms of concentric rings. There is certainly variation across the frame, but I suspect it is below what could ever be detected in a standard astro image. My actual images haven't shown any significant issues with colored rings or artifacts, but I am imaging from a Bortle 7 zone and haven't pushed the camera much beyond one hour of total integration time. Plus, in many cases I've used PixInsight's MultiscaleGradientCorrection tool and I think that process can actually remove complex color artifacts from the final results. So, the post processing on my deep space images may have removed any remaining trace of artifacts from the so-called Nikon colored concentric rings.
Of course my test results (shown below) did NOT get any such treatment, just a calibration, integration, debayer, and channel separation followed by a historgram transfer of a boosted screen transfer function in PixInsight. Without a stretch the flats looked completely uniform except for a smooth, radial vignetting from the lens. After the above processing I then rescaled each result down to 25% in PixInsight followed by another reduction of 50% using Photoshop. These 16-bit TIFF images where then output as 8-bit converted JPEGs using Photoshop
Interestingly, the blue divided by green result is showing thick horizontal bars at the top and bottom of the frame. I've done this same set of tests using a radically different lens (a NIKKOR Z 180-600mm zoom) with a completely different light source and the results look quite the same. So, these artifacts seem to be real although I don't know if they would be present in each and every sample of the Nikon Z50 II when subject to the same tests. In any case, I haven't noticed any evidence of these artifacts in my processed DSO images so again I think in actual practice these variations may be too slight to be seen.
There is certainly more work that could be done on the Z50 II to confirm these artifacts and I also have a Z30 that apparently uses the exact same sensor as the Z50. So, I could run tests using the same lens on both cameras and see what happens.
First the blue divided by green result (with the horizontal bars) and then the red divided by green.
Edited by james7ca, 03 June 2025 - 06:03 AM.