I have a new Prusa i3 MK3 and I have noticed that my prints consistently turn out worse on 0.05 mm layer heights than on 0.10 mm. The edges of the 0.05 mm prints turn out rough and sometimes stringy.
Seems similar to a retraction problem but I never have this issue on 0.10 mm prints with the same retraction settings.
What might be causing this issue?
When printing at small layer heights (high resolution), you probably need to do some test prints first to see if your normal settings work for the lower layer height. You are most probably experiencing an increased pressure build-up in the nozzle due to the nozzle being closer to the bed. A test that might be useful for you is spacing several objects at different distances to see if the retraction, which you already suspect, may be not working optimally or that the nozzle leaks/oozes an excess amount of filament due to pressure build-up. This shows an example of such a test where the nozzle shows oozing.
Tuning the extruder to alleviate the pressure could be:
When printing at 0.05 mm on my home-build CoreXY I experience much smoother prints opposed to printing in higher layer heights (less resolution), but I also get some very fine stringing, noticeable when printing multiple objects or objects with voids.
One thing that I have learned in my extensive youtubing is that sometimes the hot end can soften the previous layers. Though, take the following advice with a grain of salt as the following is just conceptual for me (I'm still waiting for my first printer to arrive to follow this advice).
Tomb of 3D Printed Horrors has a pretty good video on printing D&D miniatures that require high detail at small sizes (particularly at the 2 minute mark). His recommendation is to have 0.2 mm thick lines as thinner lines are more susceptible melting when the hot end is laying down subsequent layers. Thicker layers means more plastic to absorb the heat and less deformity. This is probably why your 0.1 mm lines look better than your 0.05 mm lines.
Another fix is to keep print speeds somewhat normal or slightly slow. A faster print head heats the previous layers less and can counteract the issue. Running at 60 mm/s may be too quick for quality prints, but running at 10 mm/s is too slow and can reheat the lower layers. Keeping an "average" pace paired with thick enough lines could help you get the prints you want. Though, finding what speeds/thickness is up to you. I don't have the experience to suggest any at the moment.
