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05-13-2010, 10:07 PM   #1
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Pentax vs Sigma 17-70mm

I had a big search but couldn't find a thread especially for this so here goes.
Im looking at buying a K7 and can save about $100-$150 (AUS-US) if I go with the Sigma.
My understanding is the Pentax is better built and constant F4 which is better at the 70mm end and also works with the built in lens correction of the K7.
Has anyone tried these two lenses together or have either to lend some sagely advice?
At the moment I'm leaning toward the Sigma as a K7 with the Pentax is abit out of budget for me - I still have a tripod/eyefi card and possibly flash to buy aswell.
However if I can be conviced the Pentax is $100-$150 better than the Sigma I can be persuaded! I'm a sucker for build quality.

05-13-2010, 11:12 PM   #2
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I have the Sigma 17-70 f2.8-4.5 for my K20D, its a pretty good lens. There is nothing wrong with the build quality either, the lens weighs over 500 grams so its not just light weight plastic crap.
I have had mine for nearly 2 years and have not had a single problem and it still looks close to new. The Pentax may be constant f4 but the Sigma has a better range overall, and the new updated version is f2.8-f4 anyway and also has HSM and OS. From what I had read about the Pentax version, it only has very slightly better IQ than the old Sigma version like mine. For the money, the Sigma is a better purchase.
05-13-2010, 11:42 PM   #3
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I cannot speak to the Sigma, as I have never used the 17-70. One thing to keep in mind is the variability of Sigma's quality control - and whether you get a "good" copy.

However, I have extensively used the Pentax 17-70. I think it is a terrific lens. Read the review at Photozone. It pretty much sums up what I think of the lens - super sharp, good bokeh, good build quality.

Only downsides for the Pentax are the distortion is pretty bad at 17mm and it is only f/4. If you would use the f/2.8 of the Sigma a lot then that may be the way to go (although the aperture switches rather quick I believe). I am not sure how distortion compares with the Sigma. Also, the Sigma has closer focusing abilities I believe (but the Pentax can focus fairly close).

IMO the IQ, bokeh and build quality of the Pentax are excellent. Not sure if it is worth the money to you though...
05-14-2010, 03:43 AM   #4
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Good to hear about the build of the Sigma-I have a suspicion the one I am looking at is the older one but its not like I need OS anyway
Still want to hear from more Sigma 17-70 owners though!

05-14-2010, 05:31 AM   #5
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I own the Sigma, as do MANY around here. It is an EXCELLENT lens. I think, even though I love Pentax lenses, that the Sigma is a better purchase. It has better close focusing capabilities (my first "macro" shot accepted in the Pentax Photo Gallery was with the Sigma), it's very, very well built, focuses fast, and it's extremely reliable.

The Sigma is the lens mounted by default on my K20D.

That being said, the Pentax is also a nice lens, it has SDM which is nice. I would have purchased it if it had been cheaper and/or wheather sealed.

The faster aperture of the Pentax is only true at the extreme tele end, and only compared to the older Sigma 17-70. The newer version is f4 at 70 mm. And the Sigma is faster over the rest of the range, which includes f2.8 at 17 mm... really not bad

Long story short, I suggest getting the Sigma.
05-16-2010, 05:43 PM   #6
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The "old" Sigma goes to f4.5 at 70mm, but only changes from f4 to f4.5 right at the end. The new Sigma stops at f4 and has OS.

So you can more or less think of the Sigma as the same as the Pentax, for apertures, except it has the bonus of being faster at wider angles.

The old Sigma got great write-ups everywhere I looked.
05-16-2010, 11:41 PM   #7
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I bought an early copy of the Sigma 17~70 three months ago. To be sure, it's a nice lens, very sharp but doesn't focus as fast as I would like. So I'm switching over to primes which is getting to be quite costly in comparison... (Tamron 90 2.8 for macro, an FA 50 1.4, a DA 40, a Sigma 30 1.4 for starters. I might let it rest at that as I do have a 10~20 also.)

The point is for the money the Sigma 17~70 is very good value, expecially in view of the convenience, not to mention macro capabilities with very good IQ.
05-17-2010, 09:51 AM   #8
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Regardless of whether a search brought up anything, this topic seems so constant that it should almost be a sticky thread. You will find advocates of the Sigma, the Pentax 17-70 and the Tamron 17-50 in almost equal numbers. They are all fine performers.

Want quiet? Get the Pentax
Need to save a few bucks? Get the Sigma
Need F2.8? Get the Tamron

Want real snap to your photos and price/convenience is no object? Get primes.

05-17-2010, 09:07 PM   #9
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Hey Tonto!

I was in your shoes a couple fo monts back. I went for the Sigma and have been happy with it so far. 17-70 is a good all around range. Very well built. I am now looking for a complement to go 70-300mm and am having to choose between the sigma 70-300 or the pentax 55-300..Déja-vu!
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