[tcwilson]

Hi.
I'm just wondering if anyone has compared the Sigma 18-35 Art lens to the Pentax 31mm Limited for image quality.

[normhead]

The 31 wins, Digitalis has a great post on it, if you can find it, and when Digitalis tests lenses against each other, you aren't going to find a better test. He's the man.

[tcwilson]

The 31 wins, Digitalis has a great post on it, if you can find it, and when Digitalis tests lenses against each other, you aren't going to find a better test. He's the man.

I don't suppose you have a link? :-)

[normhead]

I'd have to do a search like everyone else.

I have this one though if you want to know more about the 31.
http://luminous-landscape.com/sm-02-05-02/

[Conqueror]

The Sigma 18-35 is also big and heavy

FA 31mm devastatingly beautiful lens... every aspect... infinity works too

The FA 31 is also the type of lens that cannot just be measured by lab output

Sigma 18-35 might be good for Astro (due to low coma).. but there are other good options for Astro too

[normhead]

Here you go.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/270250-pent...m-f-1-8-a.html

[tcwilson]

Thank you to everyone for your quick replies! they are very much appreciated. In many respects, they are different lenses, of course; zoom vs prime, the size difference, full frame vs apc-c, etc. But I think the bottom line for most of us here is the IQ. I am wondering if Pentax will update the 31mm with the new HD coating. It would seem like a pretty straight forward upgrade in light of the new K-1.

[kraigg007]

I have them both and find myself using the 18-35mm more due to flexibility. The bokeh on the 31m is better, but the 18-35 is slightly sharper. Color reproduction is very close. Usually a Pentax lens separates itself via color and contrast, but Sigma stepped up their game with this Art lens.

I haven't sold my 31mm because I plan to purchase the K-1, but I can't let my K5-IIs go.

[Blacknight659]

I want both lenses, have neither

Personally, I have been a bit put off by the focusing problems reported by some users with the Sigma. But EVERYONE thinks the Sigma is great. Primes are awesome, but if you got them on a job where the focal length doesn't work for you, then you will be really put out. I personally can't do with out a zoom lens... YET....

[Fenwoodian]

I have them both and find myself using the 18-35mm more due to flexibility. The bokeh on the 31m is better, but the 18-35 is slightly sharper. Color reproduction is very close. Usually a Pentax lens separates itself via color and contrast, but Sigma stepped up their game with this Art lens.

I haven't sold my 31mm because I plan to purchase the K-1, but I can't let my K5-IIs go.

From someone else who's owned both, I could not agree more with your above statement.

Of course the auto focus accuracy varies a lot with the Sigma from lens to lens. While the Pentax 31mm seems to have accurate auto focus on most of these limited lenses.

If accurate and reliable auto-focus, beautiful bokeh, and durability are important to you get the Pentax 31mm lens.

But if you value flexibility more get the Sigma.

[tcwilson]

Thank you again for all your insights! From a flexibility point of view, I am fairly well covered at at the wider end of focal lengths, although not with fast glass. I have the Sigma 10-20mm 4-5.6, Sigma 17-70 contemporary (It is on the camera most of the time. It is a very nice lens. Perhaps the other question is how much better is the 18-35 than the 17-70. I suspect the point of diminishing returns is fast approaching in that arena.) I also have the Pentax 18-135 (Which I bought especially for when conditions were going to be iffy), and the FA-50 1.4 (Which I love). Yes, its a legitimate question about do I really need another lens. But I suspect people here will understand. :-) So I am really hunting for fast glass and amazing IQ. But from the comments, it sounds like both the 31mm and the Sigma Art offer that, although with slightly different strengths and weakness. So it seems to come down to the benefits of the much smaller Pentax and the fact its a FF, compared to the benefits of a zoom provided by the Sigma. In the scheme of things, its a nice problem to have. In case anyone wonders, I am shooting with a K-3.

[normhead]

Perhaps the other question is how much better is the 18-35 than the 17-70.

This type of lens is almost always a saw off. As you increase the focal length the difficulty of keeping the lens excellent through out it's whole range increase. the 17-70 is 1: 4.1, the 18-135 is 1:7.5. As a general rule you can expect the lower ratio to be better. IN this case, you can fit the 18-135 into some systems or you can justify it by it's flexibility.. but if you look at overall average IQ, low man after the 1: wins, most of the time. The 18-135, is a great walk around lens, very flexible, and has it's strong points, but it doesn't break the general rule, although phtozone charts that shouldn't be used for any final judgement, suggest the 18-135 is better from 18mm to maybe 60mm, with the 17-70 being better after 60mm.

[kraigg007]

Thank you again for all your insights! From a flexibility point of view, I am fairly well covered at at the wider end of focal lengths, although not with fast glass. I have the Sigma 10-20mm 4-5.6, Sigma 17-70 contemporary (It is on the camera most of the time. It is a very nice lens. Perhaps the other question is how much better is the 18-35 than the 17-70. I suspect the point of diminishing returns is fast approaching in that arena.) I also have the Pentax 18-135 (Which I bought especially for when conditions were going to be iffy), and the FA-50 1.4 (Which I love). Yes, its a legitimate question about do I really need another lens. But I suspect people here will understand. :-) So I am really hunting for fast glass and amazing IQ. But from the comments, it sounds like both the 31mm and the Sigma Art offer that, although with slightly different strengths and weakness. So it seems to come down to the benefits of the much smaller Pentax and the fact its a FF, compared to the benefits of a zoom provided by the Sigma. In the scheme of things, its a nice problem to have. In case anyone wonders, I am shooting with a K-3.

Okay, I own the Sigma 17-70 Contemporary lens too and it is outclassed by both the 31mm and the 18-30mm. They are not even playing the same game. I can't even remember the last time I took my 17-70mm Sigma out to shoot. I typically take my 18-35mm 1.8, 50mm 1.7, 77mm 1.8 L, and 70-200mm 2.8 OS Sigma. If I and other lenses the next ones in the bag are 8-16mm Sigma, 31mm 1.8 limited, and 100mm Macro 2.8.

The 17-70 is one of the best kit lenses / walk around lens options available, but I prefer the lenses above due to the image quality and consistent fast aperture delivered. I stopped using my 17-70 Contemporary the day I purchase the 18-35mm and I haven't looked back. BTW, I haven't had any focusing issues with my 18-35mm but many owners apparently have.

[normhead]

None of that is WR. That wouldn't work for a lot of us.

[pres589]

Now I'm hoping for an in-depth review, from Digitalis, on that 24mm f2.8 he used for a size comparison in that comparison thread.