Fastest EFCS shutter speed usable on the a7RII?

Yesterday I looked at shutter travel time for silent shutter operation on the Sony a7RII. Incidentally, we noted that the electronic first curtain shutter (EFCS) pretty faithfully emulated the acceleration of the mechanical second curtain, at least at 1/500 second.

On the Nikon D810, EFCS stops working at shutter speeds above 1/2000. On the Sony alpha 7 cameras with EFCS, Sony advises against using the capability at fast shutter speeds, but let's the user decide how far to push it.

So, let's push it and see what happens when we take pictures of a high-frequency triangle wave on an oscilloscope with the time base set to 500 microseconds (us) per division.

1/1000, mechanical shutter

1/1000 EFCS

You can see that the EFCS image has a little less exposure at the top of the image, but you probably wouldn't notice that in a real photograph. The all mechanical image is pretty even.

1/2000 mechanical

1/2000 EFCS

Now the EFCS exposure is suffering from nonuniformity noticeably, but would probably be fine for many purposes.

1/4000 mechanical

1/4000 EFCS

The EFCS exposure at the top of the image is about 1/3 of that at the bottom. This should normally be avoided.

1/8000 mechanical

1/8000 EFCS

There is essentially zero exposure at the top of the EFCS image. Not useful.

The synching of electronic and mechanical behavior over time, temperture, wear, and sample variation is an iffy business.

I used to say that users should avoid a7x EFCS shutter speeds of over 1/2000 second. Based on these results, I'm dropping that to 1/1000.