A quick specifications comparison between the new Sony A7R III vs. Canon 5D Mark IV vs. Nikon D850:
Sony a7R III: 42MP, no low-pass filter
Canon 5D Mk IV: 30MP, low-pass filter
Nikon D850: 45MP, no low-pass filter
Sony a7R III: 100-32,000 (50-102,400 expandable)
Canon 5D Mk IV: 100-32,000 (50-102,400 expandable)
Nikon D850: 64-25,600 (32-102,400 expandable)
Sony a7R III: 399 phase detect and 425 contrast detect AF points
Canon 5D Mk IV: 61 AF points w/ 45 cross-type points (plus Dual Pixel CMOS AF)
Nikon D850: 153 AF points
Sony a7R III: 10fps (76 JPEGs and/or 28 RAW images)
Canon 5D Mk IV: 7fps (unlimited JPEGs or 21 RAW images)
Nikon D850: 7fps or 9fps with battery grip & D5 battery (51 RAW images)
Sony a7R III: 4K/30p (3840 x 2160) with Hybrid Log Gamma & Slog2/3
Canon 5D Mk IV: 4K/30p (4096 x 2160), CLog w/ $100 firmware update
Nikon D850: 4K (3840 x 2160)
Sony a7R III: 530 shots
Canon 5D Mk IV: 900 shots
Nikon D850: 1,840 shots
Sony a7R III: 23.2 ounces
Canon 5D Mk IV: 28.2 ounces
Nikon D850: 32.3 ounces
Sony a7R III: $3,198
Canon 5D Mk IV: $3,299
Nikon D850: $3,296
Check out also this PDF comparison between the three cameras based on the specs listed at dpreview.
Via pdnonline
