The 61-MP CMOS sensor in the new A7C R is the same sensor you'll find in Sony's A7R V, released a few months before the A7C R. It's one of the best sensors I've tested, capable of excellent detail, with great dynamic range. The low-light performance is impressive as well, with very little noise even well up into the five-digit ISO options (the A7C R can shoot all the way up to ISO 102,400, but as you would expect, those images are very noisy).
There's nothing about this sensor that I can think to complain about. It's fantastic. The resulting RAW files are large—around 65 MB per image in my testing, with low light images being the largest. You can get this down to around 45 MB per image if you opt for compressed RAW, but at the time I was testing, no software could open these files (Lightroom and others have since added support).
Photograph: Scott Gilbertson
Raw file edited to taste in Darktable
Along with the impressive sensor comes the same processing engine you'll find in the A7R V. It has improved subject detection, including human body, face, and eye detection, along with body and eye detection for animals and general recognition of insects, vehicles, and aircraft. While all that is useful for photography, where the camera really shines is in video. The A7C R very rarely missed focus in video, and along with the A7R V, offers some of the best video autofocus currently on the market.
While there are some similarities to the A7R V, they're not the same camera by any means. The A7C R isn't nearly as capable at video. The A7C R can shoot up to 4K/60p with a roughly 1.2x crop, but that's as high as the resolution gets. That's pretty good for such a compact body, but it will be noisier footage than you'd get from the oversampled footage of Sony's larger cameras, like the A7R V and A9.
If you are looking for primarily a video camera, you're better off with the A7R V. The size trade-off isn't worth losing the sharper, higher-quality oversampled video that camera offers. If, however, you're primarily wanting to shoot still images, but have solid video capabilities should you need them, the A7C R will get the job done.
Private Eye
My main gripe about the original A7C was the tiny electronic viewfinder (EVF). On this score, the A7C R delivers only a modest improvement. It's better than its predecessor, which was virtually unusable for me, but it's still cramped and low-resolution (2.36M dots) relative to its competition, both within the Sony lineup and the larger camera market.
The good news is that the brightness has been cranked up, and what you see is clearer than it was in the original, with a slightly higher 0.7x magnification. It's a step up from the original's 0.59x magnification, but I find even the A7C R's viewfinder too small to be comfortable. It works—I can compose well enough—but it's not a joy to use by any means. This is part of the trade-off that comes with size, and to be fair, there isn't anything better out there for this size camera.