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.

PM sent for purchase.

Well, it does depend on what focal length you prefer, of course. But OP was talking about 43mm so it's a safe bet he doesn't want 135mm.

If you want longer than 43mm, choose FA 77 Limited.

Just buy the FA43 Limited and change your life as much as you need to to suit it. You will be glad you did.

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 that was the first lens everyone bought, the incidence of LBA would go down dramatically.

That Sigma is not the sharpest lens, especially in the second half of its range. Sigma also have significant variance between units. Another copy might well be better.

But it is dirt cheap so expectations should be in proportion.

Would have been nice if at the end it said "video shot entirely on the K-r". Missed opportunity there.

The FA 77 sacrifices nothing for its speed and FF coverage. Somewhere on his blog Hin Man has a shot of both side by side. OK, I found it.

That's on my list of desired camera features, along with such things as automatic hyper-focal distance calculation. The capabilities of the computer in our camera is hardly used at all.