I agree, 0.1mm is too course. I use 0.05mm all the time, which is a standard option on the web interface supported by RepRapFirmware, and I now find I need 0.025mm. I no longer use Pronterface except for debugging, but it is coded in Python and I've patched it before, so it shouldn't be too difficult to change. In the version of Pronterface on my machine, to change the Z movement amounts it looks to me that you need to change lines 27 and 168 in gui/buttons.py, and possibly also line 1468 in prconsole.py.
If you just want a button to move down 0.05mm, first go to Settings->Macros and define a new macro containing the following commands:
G91
G1 Z-0.05
G90
Then click on the + sign and the bottom of the window to add a custom button, telling it to invoke your macro.
Edited 2 time(s). Last edit at 08/15/2015 02:57AM by dc42.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].