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09-27-2012, 06:14 AM   #1
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SMC Pentax-DA 18-135mm F3.5-5.6 VS Sigma AF 17-50mm f/2.8 EX DC HSM OS

Sorry if this subject has been covered already, but I'm trying to find photo comparisons between the Pentax 18-135mm and the Sigma 17-50mm, and advice from anyone who has experience of both.

I've owned the 18-135mm for a while now and I'm pretty happy with it. However, there have been times when I've felt that it's IQ has been a bit of a letdown. I've read plenty of comparisons between the Pentax 16-50mm, the Tamron 17-50mm and the Sigma 17-50mm, (and between all of those and the various 17-70mm options) with the Sigma 17-50mm often winning the votes for overall build quality and IQ etc vs price.

But I haven't read any good conclusive comparisons between the Sigma 17-50mm and the Pentax 18-135mm. If the Sigma's IQ is consistently and clearly better than the Pentax, I'll contemplated swapping. If it's only marginally better, I'll stick with what I've got.

Any thoughts welcome....

Thanks, Andy (Bristol, UK)
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Pentax K5 + Pentax 18-135mm / Pentax DA 35mm f2.8 / Takumar 50mm f1.4 / Takumar 28mm f3.5 / CZJ 135mm f3.5

09-27-2012, 06:35 AM   #2
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Well, because we don't normally compare a professional normal zoom (for APS-C) to a walk-around zoom with WR.

The Sigma is going to have better IQ throughout the entire range. It also is faster, and sharp (enough) wide open, so it's good for low-light situations. It's AF is also likely a little bit quicker than the DA 18-135.

As for a question of how much better IQ, the DA 18-135 is often compared to the kit lens for the same range. The DA 16-45 is often considered sharper than the kit lens - especially wide open. The Sigma 17-50 and the Tamron 17-50 are often considered sharper than the DA 16-45, and 1 stop faster.
09-27-2012, 07:30 AM   #3
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these really are apples and oranges comparison because it comes down to: (1) the DA 18-135mm's extra reach (going out to 135mm) (2) the DA 18-135's WR, (3) the Sigma 17-50's 17mm extra width, (4) the Sigma 17-50's f/2.8, and (5) the Sigma 17-50's better IQ. And the DA 18-135 is cheaper than the Sigma 17-50, especially if gotten in a K-30 kit.

So:
Sigma 17-50 is better IQ and much better in low light, a little wider, more expensive, and not WR.
DA 18-135 is longer zoom, cheaper, and WR.

What is your priority?
09-27-2012, 11:38 AM   #4
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I think it'll depend on the situation. If I want to go walking in the Welsh hills for a day and think I might take a few pics along the way, the 18-135mm will probably remain the perfect partner. But if I go on a journalistic assignment somewhere (I'm a writer), and am required to bring back good enough pics for publication, from situations where the light might be v. low (concerts, indoor meetings etc) them the Sigma 17-50mm sounds like it would be ideal. Feels like I might have to get both...



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Pentax K5 + Pentax 18-135mm / Pentax DA 35mm f2.8 / Takumar 50mm f1.4 / Takumar 28mm f3.5 / CZJ 135mm f3.5

09-27-2012, 11:41 AM   #5
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It's not a bad thing - a walkaround zoom for leisure, and a professional zoom for work.
09-27-2012, 02:54 PM   #6
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Funnily enough I plan on getting the Sigma 17-50 in the next month...

I have the 18-135mm WR but I'm going to be taking the company Christmas photos in December and I need a better indoor lens in the normal zoom range. The 18-135 is good for an all-purpose walkabout but it's not quite sharp enough in the center and the corners/edges can be pretty bad.

Looking at the reviews of the 17-50 makes it perfect for event photography.
09-28-2012, 01:02 AM   #7
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Thanks Vylen, I'd be interested to know just how much better the IQ of the Sigma lens is when compared to the 18-135mm...
10-01-2012, 11:52 PM   #8
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hhmmm is Sigma 17-50 f2.8 really clearly better lens than Tamron 17-50 and DA* 16-50 f2.8? I remember there is comparision in this site and all 3 lenses did get about equal value.

10-02-2012, 03:44 AM   #9
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QuoteOriginally posted by 123jippo Quote
hhmmm is Sigma 17-50 f2.8 really clearly better lens than Tamron 17-50 and DA* 16-50 f2.8? I remember there is comparision in this site and all 3 lenses did get about equal value.
They might be of equal value, but thats only when weighed up against the pro's and con's. According to the comparison review, the Sigma isn't so good with flare, but is sharp wide open. The Tamron on the other hand is the opposite - good flare resistance but not so sharp wide open. It all comes down to what you want to use it for. My purposes is events and indoor stuff, I won't be taking particularly artsy photos involving bright light sources! And since it's sharp wide open, perfect for indoor low light. I'm not even considering the DA* though cause it's poor value for money and just way too expensive :P
10-02-2012, 03:50 AM   #10
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I use both the DA18-135WR for holidays and the DA*16-50 for work. The DA18-135 is a good walk around lens.
10-02-2012, 09:03 PM   #11
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DA 18-135 WR is ok for image quality and their focal range is really good indeed. IMHO, save your money and looking for other LTD prime lens is gonna be better.
10-05-2012, 10:05 PM   #12
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This is why I have both. For light travel and single lens general use, I take the 18-135 for the light weight, extra reach and WR. For sharpness, speed in lower light and for shallow DOF, I take the Sigma but then often feel I have to take another, longer lens "just in case." YMMV.
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