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10-31-2011, 06:10 PM   #16
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QuoteOriginally posted by dr_romix Quote
He also said if I have external flash for indoor photos and set my aperture to f8, again the IQ on 17-50 and 17-70 would be the same... do you agree with him?
Yep. I've done f/5.6 indoors at iso400 w/ the 17-70 and it's sharp.
It'll focus slightly slower than the 17-50 since lenses focus wide open....the 17-50 is faster so it'll focus faster generally...but the 17-70 isn't slow...

10-31-2011, 10:06 PM   #17
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QuoteOriginally posted by dr_romix Quote
Hello there,

I'm debating between either of these lenses for general purpose. IQ is very important. Extra 20mm on Sigma and Penatx would also be helpful in some situations. I have K-5 so not having fixed 2.8 is not a big issue..

which one do you recommend? again sharpness is important.

thanks,
I had both the Pentax 17-70 and Sigma 17-50 and I can say that the Sigma is much sharper than the Pentax. It is tack sharp by f3.5 and extremenly good at f2.8. Have never used the Tamron 17-50 nor Sigma 17-70 so can't comment on them.

Some other differences between the Sigma and Pentax:

- Pentax autofocus is a little bit quicker but Sigma is good enough
- Autofocus on both Pentax and Sigma are silent
- Pentax has a weather seal on the mount which is nice.
- Sigma is a bit heavier and bulkier but ok for me.
- Colour rendition is good for both lenses (at least to my eyes)
- Sigma for some reason overexposes slightly but that is easily corrected by the camera.

I returned the Pentax and kept the Sigma. I find that I do miss the 50-70 occassionally especially for portraits but I guess you can't have everything!

BTW I found the f2.8 really useful despite the low light capabilities of the K5. It is great for shallow DOF pictures. The problem with the Pentax was that it wasn't sharp enough at f4 (at least to me) and you often had to stop down to f5.6 or more for decent IQ but that meant you couldnt get any good DOF pictures...
06-30-2012, 08:35 PM   #18
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Greetings! I too, have a similar dilemma...I own a K-5 with some nice Pentax glass, i.e., DA*55, FA43 Ltd, DA16-45, DA50-200, and DA70 Ltd. I'm planning a trip to San Francisco, and want the following for specific scenes: Pentax 17-70, and Sigma 8-16. Does anyone have experience with these 2 lenses? I'm particularly wanting to know if the 17-70 is appreciably sharper than the 16-45, in general. If you check my site (totalqualityphoto), you'll see that I'm very much into sharpness and detail. My problem is that I must sell either the DA*55 and/or the 16-45 to help finance the 17-70 and 8-16. (I really don't want to part with any of these lenses.) Thank you for any advice!
06-30-2012, 11:18 PM   #19
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Here you go
SMC Pentax-DA 17-70mm F4 AL [IF] SDM Reviews - DA Zoom Lenses - Pentax Lens Reviews & Lens Database
Sigma 8-16mm F4.5-5.6 DC HSM Lens Reviews - Sigma Lenses - Pentax Lens Review Database

I can understand that you feel the need for an UWA although I'm personally not an UWA person and I would happily do your trip with DA16-45 and DA70Ltd; optionally add the FA43Ltd for low light.

07-01-2012, 10:15 PM   #20
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Thanks for your links and comments! That's an interesting choice of lenses, the 16-45 and the 70. Of course, I really think the Sigma 8-16 would be fantastic for such a venue! I obviously have to think on this a bit more before making a decision
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