I decided to set my ISO at 100 for my scanning. As the camera is fixed, there’s no need to worry about camera shake or vibration especially if you are shoot tethered. I then took my Sigma 70 mm macro lens and did a series of test shots from minimum to maximum aperture. Using Lightroom, I did a one to one comparison until I found the aperture giving me the sharpest image. In my case, that was f13. So, I now have my ISO and aperture settings. When scanning, I use the shutter speed to adjust the histogram until I get the results I need. As noted, since the camera is locked in position and I’m using Sony’s Remote software to trigger the a7iii, I don’t have to worry about vibration. Therefore, pick the lowest ISO you can reasonably used and the aperture that gives you the sharpest picture. Use the shutter speed as your variable and you’re on your way.