Originally posted by Botanizer K. Any suggestions for a second lens?
As someone noted, a dangerous question. How many Pentaxians are there? That's the number of suggestions you could get.
My view: Think hard about what kind of subjects you select and what kind of framing you do:
1) If you take plants and want to show them set in their habitat = relatively close image of the plant but a lot of background and surround also in sharp focus, then a wider lens, in the 15~24mm range would be the choice.
2) If you do small plants, little things that grow close to the ground, then a longer FL macro is the way to go, something in the 90~105mm range. Longer would be even better, but the options are very limited and the price skyrockets.
What would I select? I would not hesitate to select a longer macro. There are many, many options, and almost all of them are good to outstanding. Just about any macro lens of 90mm to 105mm focal length made over the past 60 years will give excellent results in the f5.6 to f11 range, and all of them will start showing diffraction induced image deterioration at f16 (although sometimes the gain in DOF outweighs the loss in IQ). SO: select Pentax, Tamron, SIgma, Tokina, Lester Dyne, just about any macro in the 90~105mm FL range, f2.5, f2.8 or f4 (makes no difference, you'll almost never use the lens wide open) in a Pentax K mount. I would recommend manual focus over AF, and because there are so many out there, and prices therefore are so reasonable, a Tamron 90mm macro, any vintage, as the most available. The lens has had an outstanding reputation ever since the very first Adaptall II version came onto the market.
BTW: Advantages of a longer FL macro: 1) greater working distance; 2) less of potentially distracting background included; 3) when getting low, the camera & lens can be up a little higher and still have the same perspective on the subject; 4) can use the focus ring at a higher reproduction ratio (this applies to unit focusing lenses, but internal focusing macros are rare and generally found only in the very long focal lengths)