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10-31-2011, 06:33 AM   #16
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QuoteOriginally posted by pop4 Quote
I've now got the Sigma 17-50/2.8 and comparatively, I find it sharper than the 17-70/2.8-4.5, however, the extra 20mm range was a little bit more versatile at times. On it's own, the 17-70 is still quite sharp and I think it would be a step up from a kit lens (not that I've ever had any experience with any kit lenses). And as for the DA* 16-50/2.8, I personally wouldn't touch it with a 100ft pole.
Thanks for your feedback. 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, 09:42 AM   #17
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QuoteOriginally posted by dr_romix Quote
".. now I'm even more confused..what do you guys think?
It's very simple. Which is more important to you / your style of shooting, the fixed f2.8 aperture or the extra range between 50 & 70mm focal length?
For me, 17-70 wins over fixed 2.8.
10-31-2011, 10:38 AM   #18
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QuoteOriginally posted by calicojack Quote
It's very simple. Which is more important to you / your style of shooting, the fixed f2.8 aperture or the extra range between 50 & 70mm focal length?
For me, 17-70 wins over fixed 2.8.
well, I have tamron 28-75 f2.8 if wanna do portrait and also I'm planning to buy Pentax 50-135 later to add to my portrait family collection.

I feel like sometime for walk around and street shooting, 50 would be a little short....
Since I mostly shoot outdoor and usually with higher f# 8 ( street, landscape ) during the day, I am not sure if I would get the same IQ on either lens.

As far as indoor shooting, how about if I set the aperture to 8 and use external flash, would there be any difference on IQ with either lens?

I think the only time I would lose a bit a sharpness compare to 17-50 would be take photos at night ( outdoor ) as I would need to raise the ISO on my K-5. even with that the f at 50mm is 4 which I don't know if that's a big difference with 2.8 anyway... please correct me if I'm wrong.

Thanks
10-31-2011, 03:55 PM   #19
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The 50-135 is a stellar performer. You'll love it (IMO).
I don't have and have never used the 17-50 or the 28-75. I love my 17-70 2.8-4.5.
Indoor under flash at f8 you'll get very similar results, I imagine.
I run into problems outdoors at night with my K10D, but if I work at it and keep the ISO down (400 or below, absolute max at 800), I can get some excellent results.

11-02-2011, 07:13 AM   #20
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QuoteOriginally posted by calicojack Quote
The 50-135 is a stellar performer. You'll love it (IMO).
I don't have and have never used the 17-50 or the 28-75. I love my 17-70 2.8-4.5.
Indoor under flash at f8 you'll get very similar results, I imagine.
I run into problems outdoors at night with my K10D, but if I work at it and keep the ISO down (400 or below, absolute max at 800), I can get some excellent results.
thanks. I think I'm going to go with 17-70.
11-24-2011, 02:02 AM   #21
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Some quick and recent crops with some basic editing.
Slight sharpening.
K10D.



12-22-2011, 10:08 PM   #22
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Do we put the F2.8-4 version in here too, or should we create a new thread for that one?

12-23-2011, 12:03 AM   #23
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I have ambivalent feelings about this lens. Yes, it's about 2/3rd faster than the kit lens, has a greater zoom range, and is relatively cheap, but there are problems at the wide end with vignetting, distortion, softness & particularly CA. These can be corrected in PP, but it would be nice if the design was sophisticated enough not to need that much help.

The lens should not really have the f/2.8. It's very soft at the edges. Here are 3 comparison shots, all taken at 17mm FL & f/2.8.




The first comparison shot shows:

Top: the uncorrected shot

Bottom: CA, vignetting & distortion correction preset I created for this aperture & FL combination in Silkypix Pro 4.

You can see that the distortion is very obvious. The top is a little darker (shaded by the overhand of the roof more), but it looks a different shade too.






The second comparison compares the centre uncorrected area, with the uncorrected top right & the corrected top right.

1. The corner softness is very obvious
2. So is the CA. This is easy to notice even in the shop - I tried 2 copies of this lens and they both have obvious CA.
3. The vignetting can be seen, but I think the roof shading makes a difference here too.


Finally, the bottom right corner. Again, the centre uncorrected area, with the uncorrected bottom right & the corrected bottom right.




The lens is still soft, but not as soft as the top right.

Dan.

Last edited by dosdan; 04-25-2012 at 02:59 AM.
12-23-2011, 06:27 AM   #24
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QuoteOriginally posted by dosdan Quote
I have ambivalent feelings about this lens. Yes, it's about 2/3rd faster than the kit lens, has a greater zoom range, and is relatively cheap, but there are problems at the wide end with vignetting, distortion, softness & particularly CA. These can be corrected in PP, but it would be nice if the design was sophisticated enough not to need that much help.

The lens should not really have the f/2.8. It's very soft at the edges. Here are 3 comparison shots, all taken at 17mm FL & f/2.8.
<snip>
Dan.
If you really want to take pictures of a brick wall, you'll need a special "Flat Field" lens.
01-06-2012, 02:38 PM   #25
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01-06-2012, 02:39 PM   #26
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10-10-2013, 01:24 PM   #27
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There are also samples posted here which was a duplicate thread not in the archive index
https://www.pentaxforums.com/forums/lens-sample-photo-archive/239280-sigma-17...ens-1-2-a.html

I will not be putting theirs thread into the archive
10-11-2013, 01:34 AM   #28
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Pentax K5 + Sigma 17-70 ( +4 Close focus filter also fitted )
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