Pentax 17-70 v Sigma 17-70

I am looking at getting an improved "standard" zoom to replace my much loved but battered 16-45mm zoom. Now I would love the DA* 16-50 F2.8, but the current cost means it is out of reach.
So, the options are either the Pentax 17-70mm F4 or the Sigma 17-70mm F2.8-F4 (now before you start John, I like Sigma lenses as I have a small number of lovely ones..:wink

So, firstly looking at the specs
Aperture - Sigma is faster at 17mm and matches the Pentax at 70mm
minimum focal distance - Sigma goes slightly closer at 0.22m as opposed to 0.28m. This could be useful.
Size - Sigma has a wider diameter (79mm) as opposed to the Pentax (75mm), but is shorter (88.9mm) as opposed to 93.5mm for the Pentax.
Weight - the Pentax is lighter by 35grammes (485g)
Filter - the Pentax is the same as my 16-45mm at 67mm, which means it will take my poloriser. The Sigma is 72mm.
Both have motor AF, which is a need (I want it quiet)
The Pentax has semi-sealing, having a rubber ring around the mount, the Sigma does not.

Both have pluses and minuses.
Pentax is lighter, slightly smaller, and will take my existing polorisor.
Sigma is faster (at 17mm), closer focusing, and cheaper (by £50)

Now I know a dedicated polorisor for 72mm would cost a lot more than £50, but I DO have a polorisor for my Cokin filter holder too, so it is not necessarily a need.

So, the questions are:-

1. Of those who have used either or both, what is the IQ like? (flickr shots show both are excellent), important are edge, contrast, centre and CA.
2. What is the distortion like at 17mm on either? The 16-45mm is pretty well controlled, so I want something similar or better.
3. which has the faster AF? the Siggy or the Pentax?

I have seen a thread of 2009, but 2 years is a long time, so people my now have either of these lenses

I am erring towards the Pentax, but you can't escape the Sigma's Price, speed and minimal focus distance.

Thoughts please

Personally I would recommend getting another 16-45

I have both the 16-45 and the 17-70 (but not the Sigma). The IQ seems similar and the extra range is handy but the frustrating thing for me is that my 17-70 often fails to lock focus in AFS mode even in average lighting. Works fine in AFC though. Yes the focussing is lovely and quiet but I would prefer noisy and reliable myself.

John (sorry for off-topic).

How come people who don't vote can't get to see the poll voting on PU without logging off ? This is very frustrating and could lead to spurious votes (someone even admitted as much on another poll recently) as people may not have anything to contribute (I've not used either of these lenses - though held the Pentax 17-70 yesterday - I was surprised at how heavy it is) but would like to see the general opinion and therefore the quickest way to do so (and let's be honest, many people would do this rather than take the time to log off/in again).

There should be a button next to the poll to see the results, for everyone not just non-members !

FWIW, I've read that the optical stabilization on the new version of the Sigma cannot be switched off and runs continuously with the result, some claim, that the lens is a battery-drainer. Worth checking, or perhaps an owner of this lens could comment?

Hi Iain,

I dont know about the Sigma but I have the Pentax- the image quality is good and it is the one lens I'd be reluctant to sell.

The comments about focussing issues are fair enough though, from 50mm onward it can struggle to lock on , there is a work around (a light touch on the focus ring sorts it)but it isnt a cheap lens so that maybe a problem for you.

I bought mine from a member on here for £280 and am very happy with it.

The Sigma maybe equally as good, or even better- I always go Pentax if I can- but some may think thats not always the best route. I am looking forward to some new PentaxRicoh glass soon.

The Tamron 17-50 2.8 also comes highly recommended on the forum and it is under £300 I think- renowned for its sharpness.

I vote for the Pentax because I really like it.

I have no experience of the Sigma, but my Pentax 17-70 is a keeper. It is the one lens I have I would not consider selling.

It does hunt occasionally, but I can live with that.
I have had it out in all weathers from heavy rain to snow and ice well below freezing when dog sledding in February and it survived it all intact.
Although not officially WR I do believe it has some sealing to it.

I have no problem with it being an F4 lens either.

Does it do it often enough for you to get a sense of what pattern of use causes it?

I've just acquired one, and I'm starting to get used to its handling, though I haven't got anything decent to show for it yet. I've noticed it fail to lock once or twice, when the field of view has been very busy, and with the lens towards the short end.

Interestingly, it happened when I was first trying it out, and it hasn't happened since.

It doesn't happen often enough for me to say for sure when, or why it does it tbh. I have never missed a shot because of it, and it certainly isn't bad enough for me to consider getting rid of it. As I said it is the one lens I would hang on to if I had to sell all the rest (though getting rid of the 60-250* would do me real pain :wink.

I have the Pentax 16-45 and Sigma 17-70 (original version).

I bought the 17-70 for the extra range at the 'long end' and have not been disappointed by its optical performance when used with the K20D. It is a little prone to flare but this can often be compensated for by slight repositioning of the camera in relation to the light source and/or use of the hand or a small piece of black card. In common with many Sigma lenses, the colour balance can be a little on the cool side of neutral for some users, but this is easily corrected for at the PP stage, as is the, IMHO, modest distortion produced by the lens; especially if one uses LR. It is a fairly weighty lens, but this is to my liking and, ergonomically, I have found it it a good partner for the K20D with grip. Overall, and not having resorted to protracted pixel-peeping, I have not noticed any deficiencies in the performance of the 17-70 when compared with the 16-45.

I have no direct experience of the Pentax 17-70mm, but, having read many reviews and user's comments, and viewed many images produced using it, have often wondered what it is that justifies its premium price tag when compared with the Sigma: perhaps it has been my good fortune to have obtained a 'good example' of the latter

Jon

I'm certainly starting to like it, but as luck would have it, I've just found a very repeatable situation where it fails to focus almost every time.

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/IMGP0742-sm.jpg[/IMG]

At 70mm, it won't focus on the red spot, but it never misses on the green spot. If I manually focus on the red spot, sometimes it locks, but mostly it hunts.

At the wide end, it doesn't have any problem with either.

It's just one of those low contrast subjects that AF sometimes has trouble with, maybe. A little disappointing perhaps, that it can't see the cross between the tiles where the red spot is, but not worth getting too worried about, I suspect.

I guess it depends on how often you want to photograph your bathroom tiles.

I shall stick it on the camera tomorrow and have a play and see if I can work out when mine hunts.

My 17-70 f4 only hunts at 50mm + and does so on a fairly regular basis. A little feather on the focus ring locks the focus and this has worked every time so far.

I think it can be had new for around £380- for me this is not a lot of money for this type of lens when you consider the silent and fast focusing- the WR sealing (not designated as such but certainly has a gasket around the lens mount at the very least) and the superior build quality.

I have a feeling that you are unlikley to be disappointed by any of the suggested lenses.

Thanks all for your comments and voting.
It seems that the Pentax is the better lens when it comes to IQ, but most of you who have it say in lower light it does hunt more than expected at 50mm and beyond. The third option of the Tamron 17-50mm seems an interesting option, although it does not have the reach of the others, it could be a better option to replace my 16-45mm. So I will look into this.

Once again, thanks all for your input.