Here are some videos. All tests were made with 1/8-microstepping and the same program on the Arduino, I just swaped the drivers.
Here is the Arduino-Code:
This is the DRV8825 set to Vref=0,5V (=1A):
After applying this mod, it got better (still @ Vref=0,5V):
Using the Pololu A4988 with this mod(Vref=0,4V):
Setting Vref to 0,64V with the unmodified DRV8825:
I can only get good results with setting the driver in FAST decay mode, otherwise it is not possible to get evenly steps in microstepping-mode. It´s still not 100% perfect, but much better then running the driver unmodified.
After modifying the drivers, I noticed, that the sound of the steppers got higher, which is some kind of annoying.
It is a pan/tilt-head, so I will just make 1-2 steps, pause some seconds, make 1-2 steps etc. To get a good and smooth video, it is absolutely necessary to have steps which make the same distance, otherwise you will see stutters in the video.
Are there some other methods I could try to get even better microstepping-results?