Recent Sony cameras have a bug that “eats” stars in RAW and JPG astrophoto images when exposure time is 4 secs or longer, or BULB - This has been slightly improved in the a7RIII HOWEVER IT STILL EATS STARS!1)2)
introduction
announced Oct 2017
similar to Sony a7R II full frame mirrorless camera but faster with more dynamic range and a new Pixel Shift mode - see below for more details on the differences
who is it for?
wedding photographers - the a7III may be adequate for this and far less expensive
portrait photographers - industry leading Eye AF tracking technology (although the a9 and a7III give more frame coverage)
landscape photographers - industry leading dynamic range and image detail in a full frame camera
studio photographers - Pixel Shift offers high detail, improved color rendition and minimal moire
videographers
unlike the earlier model, the C-AF tracking and improved burst rate now makes it an option for sports and wildlife photographers and even birders although telephoto reach may be an issue unless you are prepared to pay a lot for big, expensive lenses
released Dec 2018 addressed the bugs introduced with v 2.0
v2.0
released Dec 2018
unlocks all autofocus modes (eg. subject-tracking Lock-on AF modes, Zone and Expand Flexible Spot) for adapted lenses adapted with the Sony LA-EA3 mount adapter and these seem to work with Canon EF lenses on either the Sigma or Metabones adapter
new 'Aperture Drive in AF'which allows AF to be acquired with aperture at f/2 instead of at selected slower aperture which allows faster AF
general improvements to operation and to flash exposures near flickering light sources
version 2.0 is buggy and causes issues and has been withdrawn 3)
version 1.10:
Pixel Shift Multi-Shooting Interval reduced to 0.5 seconds instead of 1-30secs
support for bracketing during silent shooting with uncompressed RAW
support for tuning of the peaking display level for S-Log shooting
improvements for a condition where the Eye AF does not work with certain camera settings
improvements for a condition where Viewfinder Brightness is not reflected correctly in the Manual setting
improves overall stability of camera
issues
bottom of camera is NOT weathersealed - do not let it sit in a pool of water!
same sensor but 1EV more dynamic range at low ISO due to a gapless on-chip lens design and anti-reflective sensor coating and improved circuitry and processing
processes images 1.8 times faster
adds 425 CDAF points instead of 25, giving 68% of frame coverage instead of 45% coverage
IBIS improved to “5.5EV”
10fps burst rate instead of only 5fps in either mechanical or silent electronic mode but need to drop to 8fps for continuous live view
better mirror shock handling and better shutter shock handling
improved EVF and rear screen
adds HiRes mode (“Pixel Shift Multi Shooting”) similar to Olympus OM-D cameras but delivering 4 pixel shifted RAW images covering 169mp but outputs to a single 42mp RAW with better colour fidelity and texture reproduction than a single shot (ie. much less moire)
adds the a9's touchscreen focus point control and multi-selector joystick on the back of the body in place of the button-style directional pad as well as anti-flicker ability, a 2nd card slot,
AF twice as fast and extends to low light of -3EV
“Additional improvements in focusing flexibility include AF availability in Focus Magnifier mode, focal-plane phase-detection AF support when using A-mount lenses, an ‘AF On’ button, a multi-selector or ‘joystick’ for moving focusing points quickly, flexible touch focus functionality and much more,”
Sony weather sealed most of this camera very well, much better than its predecessor. BUT, for some reason, Sony left the bottom of this camera extremely vulnerable to water.