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12-09-2018, 01:14 PM   #1
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Sigma DC 17-50 mm 2.8 VS Pentax 20-40 mm 2.8-4.0

I have a wonderfull copy of Sigma 17-50 Dc HSM 2.8 ,


and recently I have driven to buy Pentax Limited 20-40 mm; 2.8-4.0.

If anybody here have (or had ) both of these lenses, I would love to hear, read from the first hand - how can this two can compare in terms of overall pic quality - and specially I'm interested in bokeh,


because Pentax 20-40 have only 4.0 at 40 mm - and Sigma have 2.8 at 50 mm - so for the bokeh - it's obvious Sigma should be better.


Then again, I'm reading about Pentax 20-40 mm limited - and bokeh - as many reviewers mentioned is also extra beatifull.


--

Sigma is wonderfull lens, but a bit heavy, and for portraiture I have Pentax 50 mm FA 1.7 (wonderfull at 1.7 ) - which came later in my collection - and squeezed out Sigma 2.8 because I have now two bodies - to avoid lens change with more serious work.


On the other hand - Sigma 17-50 2.8 - is more capable when you need ONe Lens - for shoots. Is Pentax 20-40 mm capable with 4.0 to beat 2.8 in portraiture ?



thank you all !

12-09-2018, 02:55 PM - 3 Likes   #2
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I have both. The Sigma is a different category lens - a pro standard f2.8 job.

The 20-40 is not as wide, as long, as fast or as sharp - but is light, WR and extremely well made. A better travel lens, like all the Limiteds. Mine is a beautiful silver example. I also do use it on my K-1 as a wide angle, since it works between 24mm and 40mm.
12-09-2018, 03:22 PM - 2 Likes   #3
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I have both too, and I agree withe @clackers re the Sigma. It's outstanding across the frame, even at f/2.8, and renders well in most situations. Personally, I don't find a huge amount of "character" in its rendering, but that could be due to my preferences for older film era lenses. Technically, though, the Sigma is excellent.

The DA20-40 was, for a time, the only Limited I disliked. Mine - and several others I've read about - demonstrated significant field curvature at the long end, especially when focused on distant subjects. Some have described it as "runway-style" field curvature, and my own experience confirms that. Each side and the top and bottom of the frame will be in focus at a much closer distance than the centre. Not everyone notices this, but I find it difficult to believe that it's due to copy variation. That said, I recently started to shoot with this lens with a view to accepting, rather than rebelling against, this optical quirk... and I'm growing to like it. It's very sharp (at the points where it's in focus) and produces excellent detail. You just need to use it to its strengths...

Last edited by BigMackCam; 12-09-2018 at 03:29 PM.
12-09-2018, 03:41 PM - 1 Like   #4
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While my own personal Sigma 17-50 2.8 is good for closeups including low light closeups and photos where I want to isolate something at close focus at a low f-stop, it is simply terrible at landscapes which is my bread and butter in Newfoundland. Everything in the distance just goes to a pointillist mush.

While I do not have the Pentax 20-40, the examples I have seen do not suffer from the defect my own personal Sigma does. I bought a Pentax 16-85 and even though Newfoundland has low light conditions very often from latitude and climate, for landscapes I find it FAR superior.


Last edited by jgnfld; 12-09-2018 at 03:51 PM.
12-09-2018, 05:59 PM - 1 Like   #5
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QuoteOriginally posted by jgnfld Quote
While my own personal Sigma 17-50 2.8 is good for closeups including low light closeups and photos where I want to isolate something at close focus at a low f-stop, it is simply terrible at landscapes which is my bread and butter in Newfoundland. Everything in the distance just goes to a pointillist mush.
I think just your copy, Jgnfld, so as long as Panonski buys somebody else's he'll be okay.
12-09-2018, 06:37 PM   #6
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QuoteOriginally posted by clackers Quote
I also do use it on my K-1 as a wide angle, since it works between 24mm and 40mm.
I have been wanting the 20-40 for a long time but I have sold my APS-c bodies in favor of the K1. Does it really work from 24-40 without vignetting? I have tried them in trade shows a few times. It seems like a well built lens and pretty light. Hard to believe that its is WR and all metal given the weight.

Thank you for your feedback.
12-09-2018, 08:59 PM - 3 Likes   #7
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Yeah, I'd stick to the 24mm to 35mm region to play safe. But it's a solution straight away for a modern twenty something focal length for the K-1 without going for all of the DFA 15-30. And it's light - about the size and weight of the FA31, WR and in lens motor so better than the FA31 in both those regards, and also has nine rounded aperture blades. A lot to like about it.








12-09-2018, 09:48 PM - 3 Likes   #8
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QuoteOriginally posted by panonski Quote
I have a wonderfull copy of Sigma 17-50 Dc HSM 2.8 ,


and recently I have driven to buy Pentax Limited 20-40 mm; 2.8-4.0.

If anybody here have (or had ) both of these lenses, I would love to hear, read from the first hand - how can this two can compare in terms of overall pic quality - and specially I'm interested in bokeh,


because Pentax 20-40 have only 4.0 at 40 mm - and Sigma have 2.8 at 50 mm - so for the bokeh - it's obvious Sigma should be better.


Then again, I'm reading about Pentax 20-40 mm limited - and bokeh - as many reviewers mentioned is also extra beatifull.


--

Sigma is wonderfull lens, but a bit heavy, and for portraiture I have Pentax 50 mm FA 1.7 (wonderfull at 1.7 ) - which came later in my collection - and squeezed out Sigma 2.8 because I have now two bodies - to avoid lens change with more serious work.


On the other hand - Sigma 17-50 2.8 - is more capable when you need ONe Lens - for shoots. Is Pentax 20-40 mm capable with 4.0 to beat 2.8 in portraiture ?



thank you all !
I also have both. The DA 20-40mm is a great little lens for all-around use. I bought mine specifically for its fine imaging properties, its small build but with excellent construction including WR, for use on my smaller camera bodies- the K-S2 and KP. It is good in low light also being faster than average in aperture. I agree with clackers and Big Mack, although I've never yet noticed the effects of field curvature in the shots I've taken with it.

The Sigma 17-50mm f/2.8 is an excellent choice. Just as good as clackers and Big Mack indicate. Its main lack is in not having WR. But it has better zoom range, and 50mm is a better FL than 40mm for closer portraits. Its f/2.8 will produce more background blur than f/4 can do, but its sharpness wide open at its long end of 50mm is not going to be at its sharpest. This is typical, a slight loss of sharpness at the longest FL of a zoom lens when wide open. Yet ultimate sharpness is not necessarily the goal for portrait. But we do like to see sharpness in the eyes. The DA 20-40mm LTD shows better sharpness at its long end in the Imaging Resource still-life test shot, but I think the Sigma 17-50mm could do as well at f/4 and 50mm.

For use with larger body cameras like the K-3, I would just keep using the very fine Sigma 17-50mm f/2.8. It is a great choice.
For portrait and other uses, and for very good bokeh, I would suggest you consider the wonderful DA 70mm f/2.4, which in its current HD version has upgraded to rounded blades for enhanced bokeh, and well as the superior HD coatings. That is an excellent portrait lens. You might also consider the DA 18-135mm for all around use when you don't need the speed of f/2.8 availability, and for having WR construction.


Last edited by mikesbike; 12-09-2018 at 09:54 PM.
12-10-2018, 01:22 AM - 3 Likes   #9
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QuoteOriginally posted by clackers Quote
And it's light - about the size and weight of the FA31, WR and in lens motor so better than the FA31 in both those regards, and also has nine rounded aperture blades. A lot to like about it.
And those lovely Pentax colours. It's the only DA Ltd I have but the images I see from the DA Ltd primes seem to show a family resemblance.









Never used the Sigma so I can't compare.
12-11-2018, 01:19 AM - 1 Like   #10
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The Sigma 17-50mm f/2.8 was shown in test reviews to have exceptionally low field curvature, especially for a zoom lens. But you can see how well the DA 20-40mm Limited can do wide open on the still life shot by Imaging Resource also. On the KP it is a killer. They are both very fine lenses. I love them both!
12-11-2018, 06:55 AM   #11
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QuoteOriginally posted by mikesbike Quote
You might also consider the DA 18-135mm for all around use when you don't need the speed of f/2.8 availability, and for having WR construction.
Or the 16-85
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