Recently, I bought a Sony a7r IV. The main reason was for stock photography. The high resolution along with improved focusing and biggish buffer would allow me to make better people (and other) stock photos for my various stock endeavors.
The Sony system has treated me well. I own two A7r II's for stock and other work, and two a6500's for event photography. The A7r II's aren't ideal for events for a couple reasons. The focus tracking is pretty good, but maybe not enough for fast paced people on stage. Another reason is that silent shooting is only available on single shot mode. And (admittedly a first world problem,) the files are much bigger than needed.
Well, the last problem, too big files isn't an issue with the A7rIV if you use it in APS-c mode. The files are effectively the same size as the a6500: 24 mp. Focus with the IV is even faster and more effective than the very capable a6500. And with those smaller files, the IV has no problem with buffer overflow.
So I was curious.... how about low light performance? I did a somewhat unscientific test with three setups:
- the A7r IV in APS-c mode with a Sigma Contemporary 16mm f1.4 (~24mm in FF)
- the a6500 with a Sigma Contemporary 16mm f1.4 (~24mm in FF)
- the A7r IV in full frame mode with the Sigma Art 24mm f1.4 in full frame
I tested at ISOs from 100 to 124,000 in manual mode at f2.8 varying the shutter speed to get the ISO to vary. What wasn't quite scientifically correct is that I didn't nail down the exposure and variations in lens T-values (transmissiveness of the glass) along with maybe a little variation of the ambient light from the TV in the room made for slightly different exposures.
That having been said, there wasn't a big surprise in the high ISO image quality with the A7r IV in APS-c mode. The two cameras were competitive in that area.
There was however one big surprise. With the same lens and settings, and focused on the same location, the a6500's edge sharpness was notably lacking!
Take a look at the full resolution samples here.