We sent some files to our friend Jim Kasson for analysis, and he confirms that the Sony a7R III is definitely still a Star Eater, despite several claims to the contrary that have been published online over the past week.
Looking at Kasson's graphs, one can clearly see the noise reduction kick in at 4s and above in Kasson's Fourier transform energy plots. Indeed, in our own shots of the stars with the a7R III and latest a7R II bodies, our final files look remarkably similar, only showing stars that are larger than one pixel with a few neighboring pixels. This suggests that smaller stars are indeed 'eaten' or dimmed due to a spatial filtering algorithm.
At a 3. 2-second exposure, the 'spacial filtering' (Star Eater) is mild to non-existent: noise (in dB) is similar at all frequencies, so your stars shouldn't be affected. Credit: Jim Kasson
But as soon as you hit 4-seconds, spacial filtering kicks in, which you see here as a drop in noise (in dB) at the highest frequencies (the right side of the graph, where 0. 5 f / fs is the Nyquist limit). That means the smallest details have noise reduction applied to them, causing similar Star Eater problems that were seen in the a7R II. Credit: Jim Kasson
We did our own night sky shootout of an a7R III vs. an a7R II v3. 30 vs. an a7R II v3. 00. The files are remarkably similar, though there are a some stars here and there that show up more prominently in the a7R III (see the a7R III shot below vs. a similar one from the a7R II v3. 00). While it's possible Sony may have tweaked the spatial filtering algorithm, the difference is subtle enough visually that it's hard to rule out other variables.
Ultimately, this is a missed opportunity for Sony, and something dedicated astrophotographers will want to consider when deciding between the a7R III and other options that don't have this same issue (see a similar energy plot for the Nikon D850 at 30s ). Other photographers happy with the number of stars still in their shots simply won't care. For example, check out our real-world shot from a recent trip to Sedona, AZ:
A real-world nightscape shot with the Sony a7R III and a Sigma 14mm F1. 8 lens. Sure it may be munching small, single-pixel stars, but many stars do remain, while hot pixels are suppressed. Whether or not this matters to you is something only you can decide. Click to view at 100%.
15s, F1. 8, ISO 3200, LENR off.
While we have yet to do a direct comparison of a star field vs. a camera that doesn't employ such an algorithm, we can say this with confidence: while a lot of stars still survive 'Star Eater', the a7R III continues the trend of noise reduction that dims or erases small stars at exposure longer than 3. 2s. There's some sense in this: Sony is ostensibly using this algorithm to avoid hot pixels that might otherwise riddle long exposures. But some nightscape and astro- photographers wish to be given a choice as to whether or not this form of noise reduction is applied. Alternatively, the noise reduction could (reversibly) be applied in post.
. dpreview.com2017-11-21 18:35