This is VESA mount holder for Eakins trinocular microscope from Aliexpress. Because I did not wanted some bulky holder, I decide that I will design holder for monitor arm so it will be flexible and I can move it out of my way or use it very quickly. Distance for holes are 75x75 mm because I used this arm, but you can probably use any VESA mount holder with this hole distance. 

Microscope is held in place via M3 screw which is on front side of the holder. 

You will need some M6 and M8 screws to put it together.