Bjørn: True, I never seem to get tired of flowing water at least. Or water in general for that matter.
The 105 f/1.8 has always been a favourite on the D700 (this focal length seems to fit me very well for all round use). But when I got the Df, I could finally use my 105 f/2.5 pre-AI, so I have never come around to use the f/1.8 on the Df. I can't see any reason why it should not shine on the Df as well (the f/2.5 certainly do), your remark makes it tempting to give it a try.
The f/1.8 is a big beast compared to the f/2.5 (although it is dwarfed by the AF-S Micro-Nikkor 105mm f/2.8G VR). But the sliding hood of the f/1.8 makes it much shorter than the f/2.5 (using the original hood), so both have pros and cons size wise in the field. Without the hood, the f/2.5 is by far the shortest though, due to the recessed front element of the f/1.8. You are of course aware of all this since you own both, this is more a "rambling" note to myself. Maybe this part more belongs in the "Lens Talk" category.
Asle: It seems that we think alike on this matter. I checked some of the paintings by Kåre Tveter online just now, and I see what you mean. Thanks for commenting.