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07-05-2010, 11:32 AM   #1
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17-70mm vs 18-55mm AL II

Hi,

I currently own two lenses
1. DA 18-55mm AL II
2. FA 1.4 50mm
my camera is K20D

I am very pleased with the 50mm results, and not so much pleased with the 18-55 AL II.
I have an opportunity to buy a used 17-70 for around 250$
in my country a new 17-70 costs around 800$

my questions are:
1. Approximately how much sharper will the 17-70 be over the 18-55 AL II (percent will be great)
2. How is the 17-70 compared to the FA 50mm 1.4
3. what should I check when buying a used 17-70

Any other info regarding the 17-70 would be great
Thanks,
Amir

07-05-2010, 12:05 PM   #2
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are you talking about the pentax da 17-70mm or sigma 17-70mm?

not counting the different focal lengths, for me the biggest difference between the pentax 18-55 and the 17-70 is the constant f4 apeture. the image quality should be better on the 17-70 wide open as well as at the widest and longest ends. if you want very technical comparisons i'm sure they are out there.

as for a comparison to the 50mm it's an apples-to-oranges comparison. one is an f1.4 prime the other is an f4 zoom. nuff said.

the thing to check is whether or not SMD works (the biggest point of failure) and things like scratches and heavy dust in the lens.

good luck!
07-05-2010, 01:39 PM   #3
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Honestly, comparing prime lenses to Zoom lenses, is a pointless exercise. To begin with the primes are typically faster. Second, they are optimized for their specific focal length. Zooms on the other hand, while good or even great in many cases, always will have a weak spot.

That said, whether Pentax OR Sigma, the 17-70 is going to outperform the kit lens, hands down.

07-05-2010, 06:10 PM   #4
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At that price, you should get the lens if it's in good shape. You can resell it for more if you don't lie it.

You will gain a lens that's sharper, bette with aberrations, lets more light through, has a silent AF motor, covers a wider range.

For comparisons, visit Welcome to Photozone! and read the reviews.

07-05-2010, 06:18 PM   #5
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so that means the 17--70 sdm is a worthy upgrade?

my 2 cents: between 50--70mm the DA SDM gives soft results, and between 17--50, it provides slightly better image than the 18--55 kit, f/4 is not that an improvement compared to f3.5--5.6.
07-05-2010, 06:23 PM   #6
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for that price, the 17-70mm is a steal if the lens is in good condition - no fungus, scratches or other problems. The zoom lens is more versatile and I would think the 17-70mm is good even wide-open. By all counts, it is better than the kit lens, however, compare to the FA50 1.4, which is for different application such as low light situation.

To check out whether a used lens is good, I would suggest you take your camera with you to try to mount the lens and take some test shots. Check for any visible defects, and also if you can take a small flash light with you - to check for fungus etc. Check also the zoom ring and focus ring operations.
07-06-2010, 01:34 AM   #7
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QuoteOriginally posted by shang Quote
my 2 cents: between 50--70mm the DA SDM gives soft results, and between 17--50, it provides slightly better image than the 18--55 kit
Doesn't match my experience at all.
07-06-2010, 05:46 AM   #8
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Pentax's 17-70 is a great lens! 250 is kind of a surprisingly low price for it though, be careful and check it out before buying! In addition to what others have said, check whether AF and SDM work all right - see if it squeaks when focusing, if it locks focus reliably at all focal lengths and such...

07-06-2010, 07:07 AM   #9
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QuoteOriginally posted by pbo Quote
Pentax's 17-70 is a great lens! 250 is kind of a surprisingly low price for it though, be careful and check it out before buying! In addition to what others have said, check whether AF and SDM work all right - see if it squeaks when focusing, if it locks focus reliably at all focal lengths and such...
+1

I really loved my DA 17-70. I thought it has great IQ throughout the range. But $250 (assuming we're talking USD) does sound a bit low so as pbo said make sure to check the AF throughout the focal length range. My copy had issues focusing above 50mm and it turned out the SDM motor had to be replaced.
07-06-2010, 07:40 AM   #10
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QuoteOriginally posted by shang Quote
so that means the 17--70 sdm is a worthy upgrade?

my 2 cents: between 50--70mm the DA SDM gives soft results, and between 17--50, it provides slightly better image than the 18--55 kit, f/4 is not that an improvement compared to f3.5--5.6.
f5.6 as the maximum aperture at 55mm is extremely slow for the classical 'normal' focal length. Even the old F 35-70mm was f4.5 at 70mm. In my opinion, that is the biggest weakness of the DA 18-55mm II. However, assuming there are no issues with the SDM, the DA 17-70mm is better optically. The kit lens can't even be compared to it at 55mm and f4.
07-06-2010, 05:00 PM   #11
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If the lens is working, $250 is a great price for the DA 17-70.

The main advantage to the DA 17-70 is that not only does it have a constant aperture of F4, it takes a nice photo at that aperture. Stop the DA 18-55 down to around F8, and it hangs with the DA17-70, but at F5.6 or wider, the DA18-55 is challenged. The DA17-70 is also dead quiet. All round, it is a nicer indoor lens.

Besides being dirt cheap, the DA 18-55 is one of the smallest, lightest zooms you'll find. I enjoy using it for street photography, where F8 is the norm for me anyway, and the small, light, inconspicuous form factor is a big plus.
07-06-2010, 06:57 PM   #12
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Original Poster
Hi

thanks for all the replies, it was very helpful
I think I will go for it

Amir
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