18-250mm lens. Is this good please?

I have the Sigma and it's OK but much beyond 150mm and quality really drops.
Much better is the Pentax 16-135mm bit more expensive but much better quality znd weather sealed.

I can't comment on the Sigma one as I haven't used one but I do have both the Pentax and Tamron versions which aren't bad for what they offer. Go and try the Sigma again, take some photos and see if it suits your needs.
On a miserable day it will save some lens swapping, and you'll more likely have a useful lens on should that once in a lifetime scoop appear in front of you. so don't dismiss it out of hand.

[quote="ephotozine.com"]Being priced at around £400, this lens is cheaper than 18-200mm alternatives from most camera manufacturers, plus it delivers decent quality and an extra 50mm of reach at the telephoto end. I believe this represents good value, plus as this lens is newly released, I imagine the street price may drop in time too[/quote]https://www.ephotozine.com/article/sigma-18-250mm-f-3-5-6-3-dc-macro-os-hsm-lens...

It's a very useful one lens fits all to take on holiday where perhaps luggage is limited.

When the 18-135 came out the general consensus was it didn't offer much in terms of image quality over the Pentax 18-250 other that it was weather sealed. But this is the Sigma one. Perhaps read a few more reviews?

If it's OK, see if you can negotiate a bit off and go for it.

Really only Louise can make the decision herself and something has tempted her. I have quite a few lenses covering the standard lens range in both zooms and primes. Variety is the spice of life!
It's what becomes LBA. The fact one doesn't really need it doesn't mean it shouldn't be purchased unless one is in debt.
Things to really consider are how close it can focus, maximum apertures, image quality at various f stops, whether the zoom creeps (my Pentax branded one does) and how important weather sealing, or lack of it, is to you. How comfortable it is to hold / balance on the camera. What suits one doesn't necessarily suit someone else.
If someone has one of the lenses in question and suggests it is either brilliant or a pig to use that would be useful info for Louise. But whether she should purchase one is really a personal thing only the person can decide themselves. Everyone might slate it but that doesn't mean to say she shouldn't buy it if she wants. It is what it is.
The bottom line to my input is that I have found it (my Pentax one) a useful lens to have on occasions.

I guess both Nigel and John are right.
Its ultimately your decision Louise sometimes it's great just having one lens covering all but I guess your two lenses aren't too cumbersome so the odd lens change isn't a problem.
When I go in the mountains I like just one lens same on extended travelling and there are many conditions where you really don't want to be changing lenses (dusty windy raining ) and also the chance that you might miss the shot when changing.
Price you mention is a little high but you can always pick one up on ebay for around £100 and if you don't like it sell it on again for the same.
Image quality won't improve as Nigel says and for a lot of things you'll hardly notice the slight drop in quality but t is also an acceptable macro lens.
Like John says lens buying syndrome can strike at anytime but for me trying differant lenses is one of the benefits of the PK bayonet fitting.

If I were in your position and starting out again I would not put my money in a lens that more or less does nothing different than those you already have. For a lot less you could buy a DA 50mm f/1.8 which would open up new photo opportunities such as shallow depth of field to isolate you subjects or photos with available light, even if there is low light.

Norfolk Broads: Is that on a boat or just general sightseeing. Either way there's plenty to photograph. Birds, Windmills, bridges, other boats and so on.

Sigma lens: Is this an eBay purchase, local dealer or private sale from newspaper ad or similar?
eBay is difficult unless the lens hasn't sold and you approach the seller afterwards to give you a deal.
A local dealer/private sale, just say how much you would like the lens, but can you do it for £xxx ? Always worth a try. Suggest a bit less than you're prepared to pay and hopefully end up with a compromise. Mind, if the lens is a bargain already there might not be much room to negotiate. Just watch a few episodes of the Apprentice for haggling ideas! Sure you've seen those?
Dishonest eBay sellers? Not as common as you might think with camera bits and bobs. If there's an issue you can report the item as not as described and arrange to return it to the seller. I must say many sellers are amazingly honest.

The web price at Castle Cameras looks to be £279 (perhaps a different shop with the same name or an alternative lens?)
http://www.castlecameras.co.uk/sigma-18-250mm-f35-63-dc-macro-hsm-lens-for-penta...
That's a lot more than the price you gave in the original post.

I'd have thought around £149 for a used 18-150 would be a reasonable price, be it a Sigma, Tamron or Pentax. The price you said is in that ball park. (I paid around that for my mint and boxed Tamron version.)

As others have said you might not need the lens, but if you want it it's a free country!
If it's a bit more reach you're after for the bird life, what about a Pentax 55-300?

I agree with Nigel; don't trade quality for convenience, especially as the range you'd end up with would be pretty much the same. A little story: a friend of mine had his K10D kit including two Sigma zooms stolen while on holiday in Italy, so he bought a Nikon D7200 and the Nikon 18-300 superzoom to replace it so that he didn't have to change the lens. Apart from the discussion on why have an ILC if you're only going to use one lens, the issue he's recognised is that this particular superzoom has so many optical compromises to achieve the wide range, that it's not outstanding anywhere. Compare that with the quality of what you already have, and I don't see why you need to change. My kit finds the 20-40 on the camera as a walkaround, with the 55-300 and 50/1.8 available when I need them - but the 20-40 is on the camera for the bulk of the time.

You should be able to get some really nice atmospheric shots on the Broads - maybe a tripod would be more useful in setting up for that special shot.