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08-06-2013, 01:56 PM   #1
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Deciding between Sigma 17-50/f2.8 and 17-70/f2.8-4.0 Contemporary

Hi!
I'm looking for an upgrade of my DA 18-55 kit lens (WR); with my K-7 I use mostly the DA21/f3.2 since it is tack sharp and reasonable fast and wide enough to my likings, and, its small and light. I know going into the 17-50 or 17-70 zoom range, asking for fast and sharp glass, it will be much heavier than the kit lens or the DA21. Due to performance and price consideration, I have landed on the two Sigmas listed in the thread title. (I have read the nice reviews of the lenses in Pentaxforums, thanks, great review!) Actually, in Norway the 17-50/f2.8 is since July cheaper then the f2.8-4.0 lens, about 12% cheaper. I do not know if it will last, though. Since the 17-50/f2.8 introduction price, this is half the price!

What I want to ask the audience is which one is really the sharpest? According to the test results in DxOmark, the 17-50 lens drops in sharpness wide open in the midlle zoom range, while the opposite is the case for the 17-70 lens. Many users complains further on the loss of sharpness, or is it focus, of the 17-70 lens at 17mm, focused at infinity.

Questions:
* Is it true that the focus can be manually corrected with focus switch in AF position of the 17-70 lens, but not on the 17-50 lens?
* How os the weight balance of the two lenses on a K-7/K-5 body?
* Flare: is the flare really bad on the 17-50 lens compared to the 17-70?
* How is the built quality in comparison?
* If the 17-50 lens can be bought cheaper than the 17-70, is the situation perhaps a no-brainer?

I hope someone find the time to answer some of my questions.

best regards
/Arne

08-06-2013, 02:05 PM - 1 Like   #2
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The Sigma 17-50 is bound to be sharper than the new 17-70.

Sigma 17-50 mm f/2.8 EX DC OS HSM review - Image resolution - Lenstip.com
Sigma C 17-70 mm f/2.8-4.0 DC Macro OS HSM review - Image resolution - Lenstip.com

When reviewing Lenstip's charts (which are not the final word, there are sample variations, test inconsistencies, etc - but is still reasonable to use) - The 17-50 outperforms the 17-70 at 17mm F2.8+, 30mm F4 is comparable, and the 17-50 is much better at 50mm F4.
08-06-2013, 02:06 PM - 1 Like   #3
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Should be pretty simple, do you need 2.8 more or 70 more? 2.8 for low light/shallow DOF, 70 for more telephoto reach.
08-06-2013, 02:32 PM - 1 Like   #4
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Another consideration between these two lenses, which may not concern you-- 17-70 is lighter and more compact than the 17-50.

Compare:
17-50: 77mm front element diameter, dimensions: 84mm x 98.5mm, weight: 565 grams
17-70: 72mm front element diameter, dimensions: 79mm x 82mm, weight: 465 grams

Also, 17-70 can focus a bit closer than 17-50 (22cm versus 28cm)

08-06-2013, 03:01 PM   #5
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Consider the older 17-70/2.8-4.5 as well. That lens focuses to about 2-3 inches from lens tip.
08-06-2013, 05:35 PM   #6
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Not sure if the price range is the same, but I used (and really liked) the DA17-70 when I moved from the 18-55 kit lens. Gives very nice IQ at f/4.5, and performs better than many "faster" third party lenses, which need to be stopped down significantly to get good IQ. It's also great to be able to simply set the aperture at f/4.5 in AV mode, then know that you'll get quality images no matter what focal length you zoom to. In contrast, with a f/2.8-4.0 zoom for example, you might determine that f/3.5 gives nice images when wide, but then you zoom long and it automatically switches you to the widest aperture at f/4, yielding poor IQ (because e.g. you really need f/5 at the long end).

I think you're better off with a constant f/4 aperture. Every Pentax f/4 zoom I've ever used gives nice IQ stopped down by only 1/3 stop - a hallmark of a quality lens, in my experience.

Last edited by DSims; 08-06-2013 at 05:40 PM.
08-06-2013, 11:51 PM   #7
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Weight

QuoteOriginally posted by seventysixersfan Quote
Another consideration between these two lenses, which may not concern you-- 17-70 is lighter and more compact than the 17-50.

Compare:
17-50: 77mm front element diameter, dimensions: 84mm x 98.5mm, weight: 565 grams
17-70: 72mm front element diameter, dimensions: 79mm x 82mm, weight: 465 grams

Also, 17-70 can focus a bit closer than 17-50 (22cm versus 28cm)
Yes, I am aware of the weight difference, and also size, I am a bit worried about 565 grams...
08-07-2013, 12:08 AM   #8
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QuoteOriginally posted by JinDesu Quote
The Sigma 17-50 is bound to be sharper than the new 17-70.

Sigma 17-50 mm f/2.8 EX DC OS HSM review - Image resolution - Lenstip.com
Sigma C 17-70 mm f/2.8-4.0 DC Macro OS HSM review - Image resolution - Lenstip.com

When reviewing Lenstip's charts (which are not the final word, there are sample variations, test inconsistencies, etc - but is still reasonable to use) - The 17-50 outperforms the 17-70 at 17mm F2.8+, 30mm F4 is comparable, and the 17-50 is much better at 50mm F4.
Thanks a lot for these reviews, I did not find these myself. Yes, the corner resolution is really a different cathegory, I agree. Hm, perhaps I am reaching a decision here...

08-07-2013, 12:17 AM   #9
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Optical Stabilization and Focus adjust

Hi all,
Thanks for all answers to my request on Sigma normal zoom. Some final questions from me, if anybody can comment on them:
1. It seems that the 17-50/f2.8 for Pentax mount is having its OS capability in place, while in the 17-70 lens with Pentax mount it is removed. What are the pros and cons of this? (e.g., is it possible that the 17-70 without OS actually perform better resolution wise than the tested samples with Canon and Nikon mount?)
2. I see some complaints about the short manual focus movement in the 17-50 lens, and that its has low friction, making it difficult to focus manually. Is the 17-70 lens much better in this respect? And, is it true that the 17-70 lets you "quick-shift" the focus manually when AF switch is set to AF?

best regards
Arne
08-07-2013, 02:08 PM   #10
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QuoteOriginally posted by JinDesu Quote
The Sigma 17-50 is bound to be sharper than the new 17-70.

Sigma 17-50 mm f/2.8 EX DC OS HSM review - Image resolution - Lenstip.com
Sigma C 17-70 mm f/2.8-4.0 DC Macro OS HSM review - Image resolution - Lenstip.com

When reviewing Lenstip's charts (which are not the final word, there are sample variations, test inconsistencies, etc - but is still reasonable to use) - The 17-50 outperforms the 17-70 at 17mm F2.8+, 30mm F4 is comparable, and the 17-50 is much better at 50mm F4.
I had the tamron 16-50 and it was a great lens and very sharp. I just found I was always needing that 50-70mm zone so I gave it up. My sigma 17-70 is sharp when stopped down but not quite as sharp... not enough difference to trade in my 17-70 for the 16-50mm

good luck

randy
08-08-2013, 08:58 AM   #11
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Went with the 17-50/f2.8

Actually, a local store had it on shelf with the amazing price of 2990,- NOK (should be around 499 USD). Did some testing with my K-7 and found it was backfocusing. Did AF adjustment in body at +5 and it seems to be spot on at whole range now, but I guess a little early still to fix that setting. It will be tried thoroghly in a wedding next weekend, so hopefully I am as excided also after that time. Thanks for all input to my questionare Will post some images if I am satisfied with them!

b.r. Arne
08-08-2013, 09:39 AM   #12
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Congrats on the new lens, enjoy it!!
08-09-2013, 12:10 AM   #13
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QuoteOriginally posted by seventysixersfan Quote
Congrats on the new lens, enjoy it!!
Thanks a lot! I found it is rather shorter in the long end than my FA50mm/f1.4, but I guess, this is normal, I was somewhat expecting it.

Took some test images last evening, and compared shots with both DA21/f3.2, FA50/f1.4, and kit lens DA18-55/f3.5-5.6WR. To be honest, the Sigma sharpness took my K-7 to new dimensions: the kit lens was left in the dust by the Sigma beast. It competes with the primes either on par or even better. Yes, I miss somewhat the ability to quick shift focus (while in AF, as DA21 and DA18-55 have), but I can live with that. The short throw of the manual focus I actually find ok, perhaps a plus, a long throw would have been much worse I think; no problem with focus ring dampening either. The lens weight and size I find balances well on the K-7 body, and it looks very nice, too.
b.r. Arne
08-12-2013, 12:13 AM - 1 Like   #14
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QuoteOriginally posted by norArn Quote
Thanks a lot! I found it is rather shorter in the long end than my FA50mm/f1.4, but I guess, this is normal, I was somewhat expecting it.
Just for the records: googling the issue with shorter max focal length than expected gained me the knowledge that zoom lenses (most of them) tend to become shorter (in focal length) the more narrow you focus: this is due to design issues. Primes do not in general have this behavior. So, zoom lenses in general have the stated focal length (+/- 5%) only when focussed at infinite. And here the Sigma 17-50/f2.8 seems to fit well (just a tiny more wide than the FA50/f1.4 at infinite). I'm quite happy with these findings.
b.r. Arne
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