One "all-in-one" lens for beginner

Also take a look at Sigma Lenses. They are just as good as Pentax lenses

I don't think they render colours as nicely.

And they turn the wrong way.

Can I second the Pentax/Tamron 18-250 - I personally find it a very useful and surprisingly competent all-rounder. New, the Tamron 18-270 replaces and has an ultrasonic motor and image stabilization (not that the latter is much of a selling point for Pentax users) - it has had good reviews compared to others in its class. However it is not cheap at about £400. Sigma ultrazooms tend to fare less well than others in tests.

A much cheaper option is to pick up an old 28-200 of a few years ago. (Pentax did one but it was a re-badged Tamron so you may as well go for the cheaper option of getting a Tamron in the first place) A bit limiting at the wide end (42mm equivalent) you could always make sure you had the 18-55 available.

While I agree that using a prime is very instructive, I would not advise one for the purposes you mention

The Tamron 18-270 is not available in Pentax fit, nor is it likely to be.

I have a Sigma 18-250, bought from Aliengrove. It is a good lens, but I am thinking of selling it again to free up some cash for other things.

Orly?

Got a figure in mind?

Despite what's been suggested about various lenses (all very good in their way) I would suggest that you first experiment with the 18-55m which comes with the camera.

I don't think anyone would mark this lens down and after say 3 months you will be in a much better position to descide what its limitations are for you and expand your lens aquisitions based on 'need' rather than 'might need'.

I started with a 50mm lens and it was probably 10 years before I bought a 200mm and 28mm (zooms were not generally available then)

Regards
Bernard

I'm not so sure about it. It may apear soon with Pentax badge on it. There is such kind of lens planned...

Colours are fine on the Sigma lenses I have. . I probably shoot 50:50 Sigmaentax and I've never once thought about colours being different.


Rotation of the barrel(s) has never bothered me either.

each to their own though.

I don't agree with the above at all. You still have to walk around a subject with a Zoom so that argument doesn't make sense. If anything the extra capability if a zoom will allow more possibilities and thus give more variations to teach you what works for you and what doesn't

18-250 pentax or tamron or my favourite f35-70 a cracker for no money

Lenses with huge zoom ranges look tempting, but I would rather go for better quality or speed rather than range. The kit lens paired with the 55-300 would be a great start. Some of the old manual glass is really good too and often faster than the least expensive new lenses.

There we have it, In a nutshell!
All of this advise shows that there is not an easy answer. Sorry but until you try a lens out you can't know for sure which you will find most useful. If you buy one lens, then you will use it and almost certainly like it. You will also find it's limitations as you develop your technique and ideas. One of the causes of LBA!
We all take different pictures, we all have have different ideas of how we want to take those pictures. That is why there are so many options.

Going back to your original question, A single lens for most situations there are several options from Pentax.
1. 18-250. I have not used this so have no experience. Lots of people like it but it is only available second hand.
2. 18-135. I bought one of these a few months ago and find I use it a lot. Normally kept on the camera now as it is a general purpose, compact, silent, fast focusing zoom that gives good quality pictures. The range is where I find a lot of my pictures need to be. I found that using a 55-300 or 50-200, I was often using them at around the 70-135 focal length. Previously I would be swapping lenses a lot but I find I don't need to with this one, allows me to get pictures I would otherwise miss while changing the lens and keeps the dust danger down. The range it covers, for me, is just right. The fact that it is WR also means it is dust proof. Of course the range is not as great as some of the others.
3. 17-70. Looks a nice lens, constant aperture, quiet, but for me the range was a bit short for a one lens option. I haven't tried it but it has many adherents.
4. 60-250. Nice lens I'm sure but expensive, big, heavy. Haven't tried it and unlikely to, due to the above.

You may have noticed I am happy with my 18-135. I do also have a collection of primes that allow me better quality and larger apertures when I want them but for the criteria you set in your initial thread I don't think you would be disappointed with the 18-135.

Good point - I now recall I researched it for a Canon user (my sister in law has defected - sorry!). The 18-200 XR is still around and quite cheap. Not quite as good but decent nonetheless. And it is very small and light for its class.

My only Sigmas are a 10-20 (earlier version) and a recent 50-500.

I'd say the colours render a little cooler on both of them than on my Pentax lenses.

It's not a huge effect, and I do find it surprising that it's even noticeable. The lenses are supposed to be transparent, after all

There's a new DA coming this year in the region of an 18-220 approx on the Pentax Road Map for release this year.

As to an "all-in-one" lens for beginner, it depends on what one's interests are and whether one is going for top quality or versatility.
For traditional 35mm photography the recommendation would undoubtedly have been for a good starters kit a standard prime (50mm) a wide angle (28mm / 35mm) and a telephoto (100mm / 135mm.) The 50mm would have come with the camera and the other two would not have been overly expensive to add.
With an APS-C this equates to 35mm being the standard lens equivalent, then an 18mm or 24mm being the wide angle equivalent and something between 66mm and 90mm for the equivalent telephoto; the DA limited 70 and 77mm lenses seem nearest to that. So those would be the 'quality' selection, or a zoom that covers 18-70 being the convenient solution.
So sensible choices other than the 18-55 which is itself pretty close to being ideal, would be the 17-70 or the 18-135mm.
Pentax's twin kit lens option is a good deal too offering 18-55 and 50-200 in two lenses, both much superior optically to the similar offerings from the likes of Canikon, or even better, replace the 50-200 with an 55-300. Another bargain of a lens!

John