[Lowell Goudge]

before anyone can answer there are additional questions needed to be asked, otherwise you will just get people's favourites.

1) what is your long lens / long zoom lens?

if you answer 50-135 then the 16-50 is better, if you answer 70-200 then the 24-70 is better.

if you answered DA200 or DA300, then consider how you will fill 50/7--200/300 first

2) is the gap 20-24 important, or if you follow someone on the 28-75, is the 20-28mm gap important, if so, do you ave coverage?

what filters do you have already, and what filters are you going to buy, the sigma 24-70 uses 82mm filters

[Egg Salad]

Ok.
1. Longest lens I have now is the Pentax 2.5/135, longest zoom lens the 55-300 (but will sell this one as I'm not overly satisfied by its optical performance - distortion and edge sharpness).
Like I've written several times my lens line-up consists of the 3.5/28, 1.7/50, this said 2.5/135 (and the 18-55 of course). If anything longer than 28mm wouldn't be so damn expensive I'd also own a 4/20 or something even wider.

2. 20-24 would be nice but 24-28 is satifactory and my main range (till now).
With the Sigma team I'd have a super wide to wide lens (even though not very fast with f/5.6 at 20mm and f/4 at 10mm only) and a moderately wide to tele lens.
Pentax' 16-50 only covers the very wide to short tele range. In its defence - in only one lens (wow a rhyme).

But I have to say my favourite lens in the moment is the A 1.7/50 just because it's so damn good. Was the 3.5/28 f/2 or f/1.8 with 26mm instead and sharper I'm sure this would be my absolute favourite.

What I can't say without actually owning them is if switching lenses for going wider would annoy me (or even if I'd feel the need to change lenses).

My stock of filters is clearly arranged with 3 in total - 1 52mm Skylight filter (got it with a lens), 1 58mm UV filter (send with the 135mm) and a 62mm polarizer.

Yes I know the Sigma has a 82mm thread but 77 or even 72mm would also work as its thread is clearly oversized.
Possible future buys could be another polarizer and a ND filter - but nothing planned yet.

[Lowell Goudge]

Yes I know the Sigma has a 82mm thread but 77 or even 72mm would also work as its thread is clearly oversized.
Possible future buys could be another polarizer and a ND filter - but nothing planned yet.

Note the "ovesized" filter is used tp prevent vignetting on 24 x 36 mm frame as the 24-70 is a full frame lens. you might be able to reduce this a little with a reducing ring, but don't bet on too much.

You will want a polarizer for this lens.

[Egg Salad]

I know the filter diameter is adequate on full frame but Pentax isn't so 82mm aren't necessary.

Anyways, my decision is like 80% made and if there isn't a very serious point I've missed I'm getting the....(da da da daaamm)
Pentax 16-50 (+ Sigma 10-20 if I really miss something wider).
More expensive than I would have wanted but I'll see if I want the ultra-wide range.

You voted for the Sigma team but still the Pentax' convenience - not having to change lenses - and its sealing got me.
It's going to be my main lens so being a compromise FL wise could be an advantage.
I remain insecure because of its CA, PF and other QC related issues but I just hope it won't be that bad.

So is there a general consensus that you shouldn't go for a lens older than x?
The first lenses seem to be more troubled although even later ones were faulty too.
But perhaps my chances would be better with serial numbers starting at (whatever that would be).

[Egg Salad]

Since monday I'm a proud owner of a 16-50. I got it used for acceptable ~530€ and till now it looks good. The only thing that concerns me is possible decentering. I made the famous newspaper-test today and the left side seems to be softer. But I'm not sure since it's almost impossible to keep the camera perfectly leveled. I have a tripod but at 16mm I only see it legs so I'm doing it handheld.

But here are some test pictures for you to judge:
50mm, f/2.8

36mm, f/4

39mm, f/4

16mm, f/8

28mm, f/4

50mm, f/8

50mm, f/5.6

50mm, f/2.8

16mm, f/2.8