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10-29-2011, 10:10 AM   #1
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I just got a Sigma 17-50 OS!

Hi everyone! Well I finally got a walk around lens that I like, and that is a great copy! This lens is incredibly sharp, even over most of the frame at f2.8. More important to me, it is constructed correctly, with a nice symmetric image(IE the center is sharp, then it tapers evenly to the edges) at all settings and focusses correctly around 95% of the time. I did notice something to tell everyone here: Try out your micro adjust on this lens at f2.8: it made a very noticeable difference on the edges of the image, more so than the center. I had set it to +3 after some images, and the center was sharp at 2.8, but it took until f8 for the edges to catch up. Then I tried 0 and the center was equally sharp at f2.8, but the edges were much better by f4. So I tried -1, and the center is just a little(my imagination?) less sharp than 0 and f2.8, but the edges are darn near as sharp from f2.8! Made a huge difference. So play around with this lens and the micro focus to see what it does for you. Also another note: I had tried 4 copies of the Pentax 16-50 DA*, a lens I really wanted for it's feature set. None of the copies was centered properly, and the last copy even had an AF that was never consistent. I even got banned from my usual vendor over 'excessive' returns because of that lens. The Sigma blows the Pentax lens out of the water at any setting. Just no contest. I will use the 18-55 WR for rainy days, and the sigma for everything else. Another note: I use macs with Aperture 3, and the Sigma lens has almost no color fringing, it's kinda spooky. I did not see any lateral or longitudinal fringing...kinda remarkable. And the AF is fast and quiet. I think it's an incredible buy so YMMV!

David

10-29-2011, 11:09 AM   #2
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That is a very tempting lens, glad you're happy with it. Thanks for the write up of your experience. Pentaxforums picked it as the winner of the three between the DA16-50, Tamron 17-50 and the Sigma.
10-29-2011, 11:56 AM   #3
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Congrats!

Glad to hear some of you liked the review, btw
10-29-2011, 01:03 PM   #4
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Thanks for posting! I've seriously had my eye on that lens ever since it was announced, since I think it would be a perfect partner to my Sigma 50-150mm f/2.8. I expect I'll get it eventually, but probably not until after I get the Sigma 85mm 1.4.

Don't forget to share pics when you get some good ones!

10-29-2011, 01:40 PM   #5
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QuoteOriginally posted by Edgar_in_Indy Quote
...but probably not until after I get the Sigma 85mm 1.4.
Such a beautiful piece of kit that is. My friend has one for his Canon and it's so well built, with wonderful optics.
10-29-2011, 01:59 PM   #6
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anyone recommend this over Pentax 16-50?
10-29-2011, 02:42 PM   #7
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See the comparative review:
DA* 16-50mm vs. Sigma and Tamron 17-50mm Comparison - Introduction
10-29-2011, 05:50 PM   #8
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QuoteOriginally posted by Adam Quote
Thanks Adam. I read that and it seems like Sigma is a way to go but not from the Lens review here tho.

Sigma 17-50mm F2.8 EX DC OS HSM Lens Reviews - Sigma Lenses - Pentax Lens Review Database

Please share any of your experience working with sigma vs Pentax 16-50.

Thanks,

10-29-2011, 07:21 PM   #9
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Congrats to the OP on the purchase. I've had my Sigma 17-50/2.8 for about a year now, and it's a good workhorse lens.
10-29-2011, 09:56 PM   #10
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I do recommend this over the Pentax 16-50 DA* lenses that I received because it works to spec and actually delivers what the spec sheet says it will. Maybe an in spec DA* is as good, but i've never seen one. As usual, YMMV!

David
10-31-2011, 06:37 AM   #11
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I just got off the phone with Sigma Technical support and they guy said if I have K-5 and not worried about low light high ISO, I should stick to 17-70. Both 17-70 and 17-50 use the same optics..The only difference is EX lenses have fixed 2.8 aperture and 4 year warranty vs DC lenses don't have fixed aperture and only 3 year warranty. He also said " As much as I would want to sell you 17-50 , if you have 17-70, I would hold on to that. I have the same lens and extra 20mm comes handy quite sometime. and in our lab test, I didn't notice a difference between the two".. now I'm even more confused..what do you guys think?
10-31-2011, 09:21 AM   #12
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Even with the K-5, I still wouldn't want to give up f/2.8. Faster shutter speeds and lower ISO are always a good thing, as well as having more control over DOF. So I, personally, would take the constant f/2.8 over the extra 20mm.

That's an interesting bit of information that the 17-50mm and the 17-70mm use the same optical formula. Looking at the two lenses on Sigma's website, I see that they both specify 17 elements in 13 groups. Although the 17-50mm says it uses FLD glass, while the 17-70mm uses ELD glass. FLD is supposed to be superior to ELD, so it appears that the optical formula is not EXACTLY the same, but may be very similar. This is from Sigma's website:
FLD ("F" Low Dispersion) glass is the highest level low dispersion glass available with extremely high light transmission. This glass has a performance equal to flourite glass which has a low refractive index and low dispersion compared to current optical glass. FLD glass offers superior optical performance, equal to flourite, at an affordable price.

ELD (Extraordinary Low Dispersion) glass has lower dispersion characteristics than SLD (Special Low Dispersion) glass, which Sigma has been using in its APO lenses (and some non-APO lenses as well) for many years now. It has other advantageous properties as well
.
My only question is, when I can buy a Sigma 17-70mm f/2.8 HSM?

That would take care of the constant inner conflict I have about selling my Tamron 28-75mm f/2.8 to replace it with the Sigma 17-50mm f/2.8.
10-31-2011, 10:22 AM   #13
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QuoteOriginally posted by Edgar_in_Indy Quote
Even with the K-5, I still wouldn't want to give up f/2.8. Faster shutter speeds and lower ISO are always a good thing, as well as having more control over DOF. So I, personally, would take the constant f/2.8 over the extra 20mm.

That's an interesting bit of information that the 17-50mm and the 17-70mm use the same optical formula. Looking at the two lenses on Sigma's website, I see that they both specify 17 elements in 13 groups. Although the 17-50mm says it uses FLD glass, while the 17-70mm uses ELD glass. FLD is supposed to be superior to ELD, so it appears that the optical formula is not EXACTLY the same, but may be very similar. This is from Sigma's website:
FLD ("F" Low Dispersion) glass is the highest level low dispersion glass available with extremely high light transmission. This glass has a performance equal to flourite glass which has a low refractive index and low dispersion compared to current optical glass. FLD glass offers superior optical performance, equal to flourite, at an affordable price.

ELD (Extraordinary Low Dispersion) glass has lower dispersion characteristics than SLD (Special Low Dispersion) glass, which Sigma has been using in its APO lenses (and some non-APO lenses as well) for many years now. It has other advantageous properties as well
.
My only question is, when I can buy a Sigma 17-70mm f/2.8 HSM?

That would take care of the constant inner conflict I have about selling my Tamron 28-75mm f/2.8 to replace it with the Sigma 17-50mm f/2.8.
oh well, the tech gentleman said there is not much noticeable difference between ELD and FLD glass in terms of sharpness as we do test in Sigma lab. I even called back again at the later time to talk to another tech and she pretty much said the same thing. They both said EX lenses pretty much use the same optics as DC lenses and the only advantage is constant aperture...

Since I mostly shoot outdoor and usually with higher f# ( street, landscape ) during the day, he said there won't be any difference in IQ on either lens. As far as indoor or studio shooting, he said as long as I have external flash or soft box etc, which I do, and set the aperture to 8, again there won't be any difference on IQ with either lens. The only time I would notice the difference is if I want to shoot indoors ( house, church etc ) without the flash and raise the ISO with 17-70 vs keep the ISO low with 17-50 because of f2.8;then, there will be significant difference.

He also highly praised 17-70's macro capability compare to 17-50 which is not macro.

Since you have lot more experience in the field, for general walk around, Landscape, street photo with K-5 what do you recommend my friend ? ( I also got Tamron 28-75 for portrait as you recommended )

Thanks,
10-31-2011, 02:33 PM   #14
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Sigma 17-50mm f/2.8 EX DC OS HSM Lens Image Quality

-to me it seems like sigma 17-70 is as sharp as 17-50 in the center at f4 and above ... also I did the comparison with Tamron 17-50 which appears to have more CA at the corner compare to Sigma.

Let me know what you guys think.
11-01-2011, 12:30 AM   #15
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Karen had the Sigma 17-70 OS last spring and we found it was a bad copy(mis centered) and that it had an amazing amount of field curvature at 70mm and lots more lateral color than the 17-50 OS. I cna't believe that those 2 lenses are similar/same optical formula.

David
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