Originally posted by torchdoc I purchased my K-x (first dslr) about a month ago, and I'm loving it so far. I'm looking to upgrade from the kit lens, and I think I've narrowed down to the DA 40mm f2.8 vs the tamron 17-50mm f2.8, and I was wondering if anyone has owned both and would choose one vs the other.
I use my camera casually, mostly taking pics of family/friends and while travelling. About half the time I'm indoor, half outdoor. Can't really say too much about my tendencies so far, as I'm still growing and learning.
I like the range of the tamron zoom, but the DA 40mm is so small and presumably produces slightly sharper pics. Any advice is greatly appreciated, thanks!
I don't know anything about the Tamron 17-50, but I have owned the 28-75 that others have mentioned and I agree that it is an excellent lens. I sold mine a while back and I kind of regret that decision.
I would not count on the Pentax 40 producing noticeably sharper images than the Tamron 28-75 @ 40mm. There may be a handful of primes whose image quality is simply unparalleled—the Pentax 21, 31, 43 and 77 seem to be in that category. Alas, I don't own any of them yet. The 40 is an excellent lens but so is the Tamron 28-75 and I'd be surprised if there was a dramatic difference in image quality between those two particular lenses at that one focal length. And if you absolutely have to shoot at 28mm or 75mm, well, the Tamron is much better at those focal lengths than the Pentax 40. I guess about 99% of the photographers shooting today use zoom lenses, and the image quality of the best zoom lenses, used properly, is so good today that it's hard to argue with this decision.
Even so, I've been moving away from zooms and toward primes. I think the advantage of the prime lenses lies elsewhere than in image quality.
A few of the primes are smaller and, if you will, less threatening than your average big zoom lens; the Pentax 40 has these advantages. First time I used it, my daughter (my subject) told me I didn't have a lens on the camera.
Some primes—like with my Sigma 28 f/1.7 or Pentax 35 f/2 or Pentax 50 f/1.4—are significantly faster than any available zoom lens; zooms seldom go faster than f/2.8. If I'm shooting in low light with one of these lenses and I can't use flash, the prime's advantage is decisive.
But there's a third reason to choose a prime lens, although it's a bit vaguer and more personal. Even when the prime has no particular advantage over a zoom in size or aperture, still, using primes makes me think harder about what I'm doing—about where I'm standing and how I frame the shot—and I personally find that particular challenge very stimulating. Shooting with primes is sort of like using M mode on the camera. It's not necessary, and it's nearly impossible after the fact to argue that any particular shot could not have been taken just as well using the alternative approach (zoom lens or one of the automatic modes). Still, slowing down and thinking hard about what you're doing seems to me an inherently good thing. Since I started using primes 90% of the time, I think I'm taking fewer photos overall but taking more good ones. Perhaps I'm just getting better generally, but I don't think that's the whole explanation. I think I've gotten better because I've slowed down and made myself work harder.
So it's hard to advise here. The Tamron 28-75 f/2.8 is a really nice lens, fast, really good image quality (I love dgaies's shot of the baby!) and it's versatile, as zooms are. And yet, my cameras usually have either the Pentax 40 or the Sigma 28 mounted—even though I have the Sigma 17-70 f/2.8-4.4, which isn't constant aperture but can be a very nice lens too. You have to figure out for yourself how you like to shoot.
But if you really want some help making a difficult decision, then I will help you. Get the Tamron 28-75 f/2.8 (or the 17-50 if you really need the wider angle). I shot for a long time in the 60s and 70s with fixed focal length lenses because I didn't have a choice. But today, I think the normal thing to do is start with zooms and move to primes if you start to feel you have a good reason to do so. So get a really good zoom and enjoy it. And don't blame me later if you start wishing you'd got the Pentax 40 instead. :-)
Will