Hi 2351HD,
I do relate to your sentiment. I have been hesitant about buying the 90mm macro, and after I got it didn't use it very often. Until more recently, when I had to shoot about 100 objects approximately 5in in diameter handheld in a fairly short amount of time. Glad I kept the 90mm
. The 150mm is a different sort of beast. I always thought it was sharp and any lack thereof was a result of my technique. I would usually use it for portraits at F2.8 or F4, and my subjects would appreciate... Indeed, it has a beautiful bokeh and nice drawing qualities. It's really a portrait lens. When I did some tests, it wasn't sharp at F2.8 at all and only got better at F8/11. The 120mm macro A can be had for something around $300 and may be a worthwhile addition as it is a fairly sharp lens across the entire range. Also the 165mm 67 F4 leaf shutter lens is quite sharp, but somewhat heavy. I wish Ricoh/Pentax would invest in something like a 150mm/2.8 Apo macro, how about that? Or an improved 200mm/4 macro? Just dreaming. All we are getting are some zoom updates.
I have also been looking for a sharp medium format telephoto lens in that range, and I found the 150mm/4 Schneider Tele-Xenar with adapter as a viable alternative. This is one of the batch of Schneider lenses that was built for the Heinrich Manderman Exakta 66. It sells at somewhat high prices even used, but it is beautifully sharp and has very nice drawing qualities. One of the nicest medium format lenses out there. Among the more exotic alternatives is the 150mm/2.8 Zeiss Sonnar that was originally made for the Agiflite and which is extremely sharp, and the 150mm/2.8 Schneider Tele-Xenar, which was also sold in a compact version, and which is almost as sharp as the Zeiss. It would be nice if Pentax had an alternative on a similar level, as these more exotic versions are all manual focus.
If I was you, I'd keep the 90mm for those occasional opportunities when you may just need it, and the 150mm, as it really works quite nice for portraits. I have pointed out some sharper alternatives in that range. I haven't yet closed my mind to Pentax' zoom options, but I'd rather see a super-sharp prime, ideally with fast aperture or a leaf shutter lens. .