Yesterday, I did a test of the lag of the lag of the LCD panel on the back of the Sony a7RII. Today, I’ll do the same thing for the Sony a9, and add some notes about the EVFs on the two cameras.
Here’s a picture that pretty much says it all:
This is a crop from the center of an image made with an a7RII set to EFCS and 1/500 second. That makes the time difference of the capture, from the top of the frame to the bottom, 4 milliseconds (msec). The time difference from the top to the bottom of this crop is less than 2 msec, which is small compared to the lags that we’re observing. In addition, The scope and the display of the scope are ar about the same location in the frame. Because of that, I estimate that we’re talking about a difference in time between the two of about 300 microseconds (usec). You can get a sense of that because of the verticality of the trace on the scope screen itself.
The scope sweep speed is set to 10 msec per division, or 100 msec from the leftmost part of the screen to the rightmost.
Now observe the image on the LCD panel. The green band is not vertical. It is slanted, with the bottommost part of the screen being displayed 6 msec or so later than the topmost part. That shows that the LCD panel is refreshed vertically. You’ll note that at the top of the LCD the green band is about half as wide as at the bottom. That means that I got really lucky, and caught the display at the exact moment when it was halfway through displaying the top of the band. That makes the LCD lag calculation easy; all we have to do is look at the green line on the scope and see where it is. It’s three and a half divisions over, which is 35 msec. So the LCD lag is 35 msec at the top of the display, and less than 30 msec at the bottom.
But what about the EVFs on the a7RII and the a9? Do they have different lags from the LCD panels? I tried to figure out how to shoot the image in the finder and the scope itself at the same time, but I couldn’t make it work. I am open to ideas.
I did notice a few things while I was playing around with the finder images:
- The a7RII finder refresh rate is twice that of the LCD panel.
- The a9 finder looks entirely different than its LCD display when viewing the scope. It doesn’t look stroboscopic like the a7RII finder, but much more like looking at the scope itself.
- Half-pressing the shutter release button of the a7RII can double the refresh rate.
I wish I had more clarity on the EVF lag, and I’ll be thinking about how to get it. I’m sure I could gin up something with a half-silvered mirror, but I don’t that’s worth the effort.
[Added 10/11/17: I have ordered a device that mounts to the front of a lens using a 77 mm filter ring, and produces a stereo pair at the focal plane. I hope to be able to find a focus point where one half of the pair, which is looking at the scope directly, and the other half, which is looking through the camera finder, will both be sharp. Stay tuned.]