Originally posted by crossing I have Pentax k-x , 18-55 kit lens, fa 50mm f1.4 ,
I would like to buy new lens that i can use it 90% of time, i hate 18-55 kit lens...
I think abaut :
Sigma 18-50mm/F2.8-4.5 DC OS HSM ,
Sigma 17-70mm 2.8 DC,
Tamron 17-50mm f2.8 XR Di II LD (price almost double compare with 18-50 Sigma..)
what do you think ?
Like the previous posters (Ash and Marc S.), I'm wondering what you find lacking in the kit lens. Also, what kind of photographs are you interested in taking, in what kind of conditions?
I have the Sigma 17-70 DC f/2.8-4.5. It is quite a good lens, for the money, especially, one of the only zooms I have kept since I started trying to use primes most of the time. Of course as Marc points out, it's got a variable aperture: f/2.8 at the wide end (17mm), stopping down to f/4.5 at 70mm. If you are shooting mostly outdoors in good light, or with flash, this may not be a problem at all. I use this lens mainly as an all-purpose safe choice to carry when I'm not sure what I'll need, for example, for trips to the park or the zoo.
But there are lots of other lenses to consider, and the idea of having a lens that you use 90% of the time is, well, a bit contrary to the whole point of having a dslr in the first place. I mean, considering how good the high-end compact, fixed-lens cameras are these days, one of the main reasons to switch to a dslr is so that you can change lenses when you need to.
If you want to shoot in bad weather, look for one of the Pentax weather-resistant lenses.
If you want a fixed aperture lens in the wide-to-normal or normal-to-near-tele range, consider the justly famous Pentax 16-45 f/4 or the also excellent Tamron 28-75 f/2.8. The Pentax 16-45 f/4 is a stop slower but considerably wider. It makes a terrific alternative to the kit lens.
If you really want a lens that can (almost) do it all, then consider one of the superzoom lenses with an 18-250mm zoom range: Sigma, Pentax and Tamron all make one. I've owned the Tamron and the Pentax, which are supposed to be more or less the same lens (Pentax uses the Tamron lens but puts its own branding on it). Very good, very versatile, again for outdoor shooting in good light.
Or you could consider getting a "normal" focal length prime lens and discover the excitement of shooting with primes. The Sigma 28 f/1.8 and the Pentax 40 f/2.8 are the two lenses most likely to be found mounted on one of my cameras at any given moment.
Will