The folks who supply fluid mounting kits make the point that there is a plane of best focus of consumer flatbed scanners, and that finding this exact plane is very important fir best results. And to that end they supply testing kits and shims to adjust the scanner to the plane of best focus. If anyone has actually used and found one the testing kits to be useful I would appreciate your comments.
Let me say from the start that I am a bit skeptical. In my own tests of two different flatbed scanners, an Epson 4870 and a Microtek 9800XL, using a resolution target capable of much more definition in lppm than either scanner, I found no difference in results in terms of lppm with the target placed faced down on the scanner glass, elevated 1mm above the scanner glass, and elevated 2mm above the scanner glass. In all three cases, when scanning at maximum optical resolution, I got resolution of about 21 lppm with the 9800XL, and just under 40 lppm with the 4870.
If your experience is different from mine, please let me know. I am truly interested in getting the most possible out of my scanners and if there is something faulty in the logic of the testing I have done I would like to know it.