best kit lens replacement

Sigma 10-20mm, will open up some new options.

The 16-45mm will be a slight improvement over a good kit lens.

Check the kit lens you have if you can, there are good and bad ones about. If you have a bad one you could get a good one for just a few quid.

You can fill the longer end with cheap primes, 28mm, 35mm, 50mm. All standard all cheap.

There is no doubt the DA16-45 is excellent in all respects except it's rather wonky build. it improves over the kit in corners and extra 2mm wide, which is significant.

However after getting a DA12-24 I never use it. Instead I skip up to the FA43 if I need a narrower focal length. You will see something similar in many pro camera bags: a wide zoom, tele zoom and fast fifty to cover the middle.

Of course the price cannot compare, but SRS have decent used deals.

If people are interested, I think if you try hard you can still track down new 16-45s. I recently bought a Samsung one from Park Cameras for a lot less than LCE are charging for a secondhand copy. And, aside from remembering again how good these lenses are, was also pleasantly surprised at the build quality - it feels rather tighter than the Pentax version I had a while ago but perhaps that's because it's new. I think Park still had another one or two left.

I have the sigma 17-70mm on my GX-20 and I think it's a great lens.

I did have to adjust the focus to +9 but now it's perfect, nice and sharp all the way through the range.

The close focusing is nice too , at 70mm I can focus on objects that are practically touching the front element.

Paul C, I don't understand "adjust the focus to +9".
I'm not sure what you mean.

A number of later Pentax cameras allow fine adjustment of lens AF accuracy to deal with front or back focus issues, either as a menu feature (K20D onwards) or as a firmware 'hack' (K10D and earlier).

I agree, the 16-45 is a great kit lens replacement, VERY sharp.

"I was a bit disappointed after comparing the results of my k-x with a friend of mine (sony A900 with excellent lenses), Mostly about contrast and sharpness."

A "full frame" sensor (eg. Sony A900) with excellent lenses is going to knock spots off your camera/lens combination pretty well whatever you do because of the much larger sensor size. You can u/g your lenses but you with a sensor 2.3x bigger than the K-x & twice as many Mp to compete with you're going to have to get very good glass.
Does your friend have zoom or prime lenses?
I use option 1 (with other lenses: 105 macro, 70-300, FA50 & FA31 Limited) but you need to decide what you're using the lenses for & how much quality you want or can afford.
Of course you can always wait for a full frame Pentax so if you buy lenses make sure they will accommodate a full frame camera without cropping the image.

Could be a very, very long wait .

"Could be a very, very long wait"

Indeed it could Gwyn. Who knows? Only Hoya & they aren't talking. They did pour cold water on FF some time back but I suspect it's coming..................

How were you comparing? If you are shooting RAW on the K-x and have the PP skills (not difficult), you can get excellent images with a bit of sharpening and slight contrast boost (depending on the image). Colours will be excellent, likely better (eg more saturated) than Sony with top lenses. Zeiss are coolish (eg blue cast) which is a nice look as well -- if you want it!

Sharpness? That is largely down to operator skill and ensuring you have the region you want in focus perfectly. Unfortunately the K-x does not allow AF adjustment per lens, but with the firmware hack you can ensure that your most used lens is perfect. This makes a significant difference!

Sharpness at the centre focal point is much the same for any lens, except for real rubbish ones or those that are out of whack, tests notwithstanding.

Are you comparing on screen with high magnifications? Full-frame will win, as already stated. Are you comparing by printing out images at the size you need? APSC works perfectly well for me at sizes up to A2. And for 4x6" snapshots all you need are images of a couple megapixels.

I strive for perfection as much as anyone, but I don't beat myself up for not having gear I could not afford anyway. Comparing to full-frame is pointless unless you are actually planning on purchasing such gear.

Just get a few K series primes. The K 55mm f1.8 on my K-m demolished the best Minolta 50mm on a friend's A900!

It also comes down to printer quality. I recently had to do a major nozzle clean on the big printer (Epson Stylus CX3600) but it still won't touch the Canon IP90 I use with Pictbridge to print the best photos out.

I upgraded from the 18-55mm kit lens to the 16-45 and am glad I did, as the higher image quality is noticeable!
It spends a lot of time on the camera!

Graham.

I upgraded to the 16-45mm lens, using it all the time now.

Regards

I'm surprised no one has mentioned the Tamron 17-50. If you're considering non-Pentax lenses (and I see you mentioned Sigma 17-70), then you should definitely look at the Tamron. Not too dissimilar in price to the Pentax 16-45, but constant f2.8 and extremely sharp.