[uchinakuri]

Thank you all for the responses! The pictures posted are indeed very convincing shots of what is possible with extension tubes -- at least, to my untrained eye.

I'd like to throw in close up lenses into the mix. For example, I was browsing the forums and saw this post: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/79076-raynox-h...40-helios.html (Scroll a bit down to the shot of the blue flower and the bee)

It seems that shot was taken with a FA77 and a close up lens. I've been reading good things about the Canon 500D close up lens. Even though it's Canon, can something like that be used on Pentax lenses?

[Frogfish]

Forget the +diopters they degrade IQ but the Raynox (150 / 250) are great.

Personally my advice would be to buy the Tamron 90 Di 1:1 macro. Fabulous macro lens, superb portrait lens, great street lens, cut your throat sharp and a wonderful bokeh. It covers many of your proposed uses. You can add the Raynox to that to get about 3:1 macro - now that's great magnification !

[RioRico]

Diopter lenses are simple pieces of glass, uncorrected for optical aberrations. They have their uses, where extreme sharpness isn't needed. Raynox adapters are corrected and quite good. Their clarity is similar to what you get by stacking a reversed secondary onto a primary lens, but their magnification is limited.

As for buying a macro lens: modern AF lenses are great. IMHO they are also overkill (and overpriced) for much macro work. I use manual glass. My M42 Vivitar-Komine 90/2.8 1:1 cost a whole US$3 on the bay, shipping included. The M42 Macro-Takumar 50/4 1:1 that arrived a couple days ago set me back US$55 total. For more oomph, I'll maybe stack a US$8 Vivitar-Komine 28/28 (Canon FD mount) with a US$3 reversal ring on a US$18 Hanimar 135/3.5 for ~5x, or stack a US$7 Super-Takumar 55/1.8 for ~2.5x. Such a setup thus costs less than some replacement lens hoods.

No, wait, forget that. Buy a new Pentax 100 macro. Pentax needs your money.