Thanks for the articles. This answers my question.
It's a pleasure. Let me take it one step further and answer a question you didn't ask, but may have thought of. That question would be: "Now that EFCS has gotten rid of the first curtain's vibration, does the accelleration of the second curtain at the end of the exposure cause any bad effects?"
The answer is that the effects are measurable, but not very significant unless you're using really, really long lenses. Here are MTF50 comparisons with the Zeiss 135mm f/2 Apo Sonnar set to f/5.6 on a D810 with EFCS engaged. I'll have the details up on my blog site in a couple of days -- I'm a couple of posts ahead now.
The graphs compare MTF50 at various shutter speeds with that when the target is illuminated with a 1/13000 second strobe burst. Both the continuous and the strobe illuminants are 5500K to prevent diffraction differences from affecting the result.
The first graph is for horizontal lines, and the second is for vertical ones. The thick lines are the mean values, and the thin ones are three standard deviations higher and lower. You can see that the higher shutter speeds are more problematical than the lower ones, though the differences are small. That's because the time the second curtain is moving is a larger portion of the time the shutter is open when the shutter speeds are shorter.
You can also see that, since the shutter moves up and down, it affects the horizontal lines a bit more than the vertical ones.
You can also see that the effects are very small. One day, we'll have global shutters, and the curves will be virtually flat.
Jim
