Sony had a big launch event in NYC back in July for their new a7r IV, which uses the smallest (yet full frame) of their latest and greatest triad of back illuminated CMOS sensors, with 61 Mpx. This is essentially the same sensor as the IMX455 used in the just-launched QHY600 cooled astrocamera, but with phase detect autofocus pixels added for the consumer camera market. The technical part of the launch video is worth watching; they claim 15 stops of dynamic range, implying either really low read noise, a large full well, or a combination of both. The a7r IV also has on-chip 16 bit ADCs. Here's a link to a video of Sony's NYC launch event:
I have been eyeing Sony's new triad of cutting-dege BSI CMOS sensors since they first appeared on Sony's roadmaps a few years ago. While the a7r IV is pricey at $3500, that is still well under the $5000 for the upcoming "Photographic" version of the QHY600M/C, and so the a7r IV had the potential to be a really great camera for astrophotography.
While retail a7r IV's are not yet shipping in the US, with general availability here "in September", a number of advance copies have made it out to reviewers and some folks in other countries. On September 14th, one user, Jim Kasson, went to the effort to check for any star eating issues. He reports a dramatic change in behavior once the exposure time reaches or exceeds 2.5 seconds. You can read his report here:
Petapixel also picked up on this yesterday:
That's a real shame. Sony hasn't listened to the needs of the astro imaging market to date, and seems to be bent on continue to ignore it. All it would take is a firmware option to turn off this feature (for us, bug). With no cameras yet shipping in the US, and no manual online, its remotely possible that such an option is buried in their menus, but I wouldn't count on it.
Jim Kasson's blog not only checked into the star-eating issue for the new a7r IV, but he also tested a LOT of other aspects, many of which are relevant to astrophotography. You can check out his full set of testing here:
Kasson goes deep in deriving full well capacity and read noise vs ISO setting, fixed pattern noise, read noise versus self-heating, and a number of other parameters that we care about. I'm still digging through all of his findings, but it does seem clear that Sony's claim of 15 stops of dynamic range is essentially marketing nonsense, and that the actual dynamic range of the a7r IV is only marginally better than its a7r III predecessor, although both are still quite good in DR compared to other cameras.
I mentioned at the outset that the a7r IV is based on the smallest of Sony's latest triad of impressive BSI CMOS sensors. They may well retain commercial camera use of the full frame model for their own cameras, but for the larger two, they are offering them to other camera makers. Fuji, in particular, will be launching their GFX 100 in November; this uses a variant of the 55 mm diagonal IMX 461, but with autofocus pixels added for consumer camera use. It is much more expensive ($10K), but still way below the price of other medium format cameras from Phase One and Hasselblad. That large diagonal will challenge optical systems, but Tak and others could handle it with ease. I have a TMB 130 f/6 APO with a Riccardi large 0.75X reducer that could do so as well.
Star eating is a camera software issue, not anything intrinsic to the sensor, so these new Sony BSI CMOS sensors may yet find use in astro imaging. In a PM from a CN poster with a Fuji GFX 50 (earlier Sony sensor generation), he states: "I can tell you that the Medium Format is a total game changer and that the color reproduction is second to none. Fujifilm in generally are really pushing their system for astro imaging, especially in Japan.". That is encouraging, and jives with what I am hearing that Fuji's stock IR filter lets in a lot of Ha. So there's still hope, but at a price. In the meantime, Sony needs to hear from us to add a disable feature for "star eater".
All the best,
Edited by Coconuts, 17 September 2019 - 06:51 AM.