Originally posted by Azzy My main priority is to get as much magnification with highest IQ possible, I will be using it to take shots of anything from insects to some random object around the house.
Just about all real macro lenses (and enlarger lenses) have good-to-great IQ. (So-called macro-zooms aren't real macro.) Most Pentax compatible macro lenses stop at 1:1 (1x) magnification. For more magnification you need either extension (tubes and/or bellows) or reverse-stacking. I talk a bit about these options in the CHEAP MACRO article.
Quote: Having infinity focus is not necessary. Being able to use it as a portrait lens is a plus but not really a big deal since I already have FA77
All real macro lenses reach infinity focus, unless you add extension to them.
Quote: My budget is ~$500 including flash (I don't own one yet, I was hoping to get into strobist as well), can anyone recommend a good combo for this ?
A Lester Dine dental-macro lens with a built-in ringflash. Can't be beat!
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Besides budget, the basic decision points are 1) How close do you want to work? and 2) How easy do you want it to be? For easy exposure, especially with flash, you want an A-type or AF lens. For close (studio) work, you want a 35mm or a Fifty; for further (field) work, you want a Hundred or longer.
A great short lens: A50/2.8 macro. A great longer lens: A100/2.8 macro, but that's beyond your budget. Otherwise, a variety of A-type and AF macros in 90-100-105mm are available. Others will push their favorites here; I have no recommendations.
To get more magnification with any of these, add A-type extension. As I mention in the CHEAP MACRO article, the cheapest option is to get a couple (or more) A-type 2X TCs and remove the glass. They will retain complete exposure and aperture control.
Flash is a tricky component and I have no recommendations. Others will push their favorites, which may include customized mounts and light-channels and whatever. I get by with my P-TTL Pentax AF360 and a TTL ringflash.
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So, my recommendations for your desires and budget.
* For maximum magnification: Any affordable(?) 28-35-50-55mm A-type or AF macro lens; 2-4 deglassed 2x TCs.
* For farther work and lotsa mag: Any affordable 90-100-105mm A-type or AF macro lens; 4-6 deglassed 2x TCs.
* Whatever flash is most recommended. I'm agnostic here. And a tripod. Don't forget the tripod. And a funny hat.