So I have about $500 to spend on a new piece of kit and am trying to decide the best way to spend it. Currently I have a k-x, Sigma 50 mm f1.4, and DA 21 mm, and a 18-55 kit lens that is never used. I mostly use it for family and travel photography, nothing serious just a DWAC. I have narrowed the choices down to either getting a standard zoom to sate my wife's disdain for primes (either Pentax 17-70 f4 or Tamron 28-75 f2.8) or a flash to fill out that piece of the photography puzzle (either pentax AF 540FGZ or metz 58).
The 21 I mostly use when shooting pictures and video indoors in smaller rooms or if I go out solo since it is more compact, it is a better focal length because my subject often decides to run at me if I get far enough away to compose a nice shot with the 50 mm, and I don't have to worry about it banging into something if I have to chase after a kiddo. I use the 50 mm most of the rest of the time because it is faster and equal or superior in IQ to the 21 in most situations. My plan was to get a flash this year and get either a FA 77 or Sigma 85 mm prime next year, but I hesitate to go through with that plan because it seems like there is a lot of ambivalence around the 540 that it is over priced, outdated, and has a few shortcomings with build quality. I was really hoping that they would have released a successor by now.
I am of the mindset to keep waiting 1 more year for a new flash which is why I am considering the zoom lens. With the zoom lens I was looking at these two and am leaning towards the Tamron because I like the results I have with the FF lens on an APS-C sensor (sharper across the whole frame and virtually no vignetting) with the Sigma as well as the peace of mind that if Pentax released a FF camera sometime in the next 5 years I could upgrade to that without buying new lenses.
The thought crossed my mind to sell or trade the 21 mm for one of those zoom lenses (to make my wife happy) and get the flash too, but that thought got all the way across my mind and the 21 isn't going anywhere
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I get some advice to people more experienced and skilled than myself if I am being too picky/optimistic in waiting for a new flash because the 540 is great or if I should just go for the metz and be happy. Otherwise, what are your thoughts on these two lenses.