[MadMathMind]

I'm in the early stages of considering purchasing one of these fantastic primes. I've read reviews and FA seemingly has better bokeh, an important attribute in a lens like this for me. There's a couple of major pluses for each lens:

Sigma Art

• Price (almost $400 less)
• Able to use my existing filters with step-down ring. The FA's built-in hood means I can't use my collection of 72mm filters with a step-down ring. I have an ND Grad and a Variable ND filter I think could be useful with a fast prime. Otherwise, using wide apertures for "trick shots" in bright light may not work out well.

Pentax FA:

• Legendary image quality
• Compact, metal-build quality
• 31 mm is probably a better focal length than 35mm on APS-C

The small different in speed is not a big deal, as I would most likely use the Sigma stopped down slightly anyway. Pretty sure the FA could be used from 1.8 on, although it's likely I will also be at 2.0 or 2.2 (do these modes exist?). As a side bonus to the Sigma, I already have the 17-70 Contemporary, so once the USB dock is released for K mount, it might be a good purchase.

The slight difference in focal length is one I'm undecided on. I plan to use this lens in two contexts, mostly: for low-light shots when things are moving (candid shots at gatherings, aquariums, other animals) and for artsy bokeh shots--the ones where the 17-70 just cannot go because its too slow. It's always possible to crop too wide but not always possible to back up, like when backing up involves falling off a cliff or standing on an exhibit. Can anyone chime in on problems with a 35?

The price is something I can get over, but the filters...I don't want to purchase a second set of these filters, both for cost (they were about $120 each) and because I don't want to carry more stuff in the bag. The ND filters aren't used a lot, but obviously I have them for a reason, and it seems poor to be limited on what would be my "best" lens. So...my question is: is the FA's image quality THAT much better? I've read the reviews and they seem to be pretty close, although the FA has an edge. But if I have to get new filters for it, is it $600-700 better?

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Last edited by MadMathMind; 01-12-2014 at 05:40 PM. Reason: Make shorter

[Na Horuk]

Can you go to a store and maybe touch, hold both lenses? Maybe even take a snap or two with each? I think that might be your trigger moment - where you will know which lens is for you
If you don't have a store with these lenses available, then look at sample photographs. The two lenses should be quite different in rendering.

[stevebrot]

31 mm is probably a better focal length than 35mm on APS-C

I guess if 31mm works well for you, it is a "better" focal length. I have both 28mm (supposedly close to the ideal normal for APS-C) and 35mm lenses and prefer the 35mm for general shooting. It is all a matter of preference and one that you might want to explore carefully before committing big money for a lens.


Steve

[Adam]

The two lenses are very close to each other, but I think the Sigma 35mm is superior optically, arguably being the sharpest lens available for Pentax at the moment. I personally prefer its bokeh and I've been able to capture some fantastic portraits with it.

The main thing to consider IMO is the size. The Sigma is huge and it feels really over-dimensional on just about any Pentax body. The 31mm, on the other hand, is elegant and compact. But then again, it doesn't have silent AF.

The slight difference in focal length is one I'm undecided on.

The difference isn't big at all, but if you're planning to do close-ups and artsy bokeh shots most of the time, I'd go with the Sigma. It focuses closer and it feels like a fifty on film.

Adam
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[Apapukas]

I've used both of these lenses and it is really hard to say which is better.

I will try to explain why.

Image quality:

Even though, sharpness is very good on both lenses, bokeh is better on Sigma.
Color rendition. Well, both lenses render colors really nice, but I prefer the colder look that Sigma produces that the warmer from 31.
CA - Sigma is miles away, 31 suffers from CA pretty badly.

I give a point to Sigma here.

Build quality:

31 is all metal, looks like a jewel. Even though usually suffers from wobbly front element which isn't acceptable for such an expensive lens. Also, there is a little movement in the focus ring when camera is in AF mode (no QS for the 31). Yes, these are small things, but for 1.3K $ lens, they are hardly acceptable (IMO).
Sigma is mostly plastic, but has a metal mount. No wobble or anything, feels very solid. Features internal focusing, quick-shift which makes the lens feel high quality and very well build.

Hard to say which is better. I'd say it is a draw.

Auto focus:

31 is screwdrive, Sigma - HSM. Both focuses very fast and both lenses didn't need any AF adjustments (on K5IIs).

Win for Sigma (for silent focus)

Joy of use:

Sigma is a very large lens compared to Pentax. Heavy too. Grip is necessary for comfortable use (IMO). So, it is a little tiring to use it for two or more hours. The biggest drawback for the Sigma is that you may not have it when you need it.
Pentax 31 is small and light. It will fit in any camera bag, there is really no problem having it always with you.

Win for Pentax. Quite subjective, but I enjoyed using the 31Ltd a bit more.

Conclusion:

So, even though the overall score is Sigma 3, Pentax - 2, I'd say there is no real winner here. Both lenses are very good and you should get the one that suits your priorities better

Hope it helps

P.S. information written above is 100% subjective, based on my semi-pro use and it is absolutely normal if it varies from yours

[Paul the Sunman]

The rumour is that the FA's will be refreshed soon, presumably with HD rather than SMC, hopefully with better CA control and quick shift, and possibly with DC and WR. The last two seem unlikely. Anyway, I've decided to wait to see what these changes bring before making a decision on this question.

[skyer]

I think that 31's IS one of the strongest points of the lens. These CAs give a unique and very pleasant color rendition that the lens is so much famous for.

[LeRolls]

I've only been using the 31 for a little over a month now but I love it. My choice to go with the 31 over the Sigma was mostly because I preferred the classic and unique rendering that it offered over the 35 which to me comes off as a bit sterile and lacking in character when compared directly. The 35 seems a bit sharper but the 31 is considerably smaller/lighter and IMO has better build quality. The price difference really isn't that drastic if you can find the 31 on sale or used. Both lenses are great either way though.

[azerak]

I can see that you want a quality outcome. If that is what you want, then Sigma it is, since you did not mention anything about weight.

[Kozlok]

If you are willing to lug around a monster of a lens, the upcoming Sigma 18-35 may be just the thing. Appears to nearly rival the 35 at 35, and just gets even better at the shorter end. Every review I've seen for it says it will be a peach. We should get it in K mount before the end of Q1 2014.

[Rondec]

There was a comparison of these two lenses. I think they are pretty close on APS-C. On full frame, I imagine the Sigma would have a lot stronger corners.

I happen to like the rendering of the FA limited better, although it is a lot more prone to PF and CA.

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/228193-boke...igma-35-a.html

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/226388-quic...1-limited.html

[jeffshaddix]

Not to feed the fire, but I recently had the same decision to make, and went an entirely different direction: Zeiss 35/2 ZK. It's around ~$700 on ebay new, as sharp (or almost) as the Sigma, very sharp wide open at f/2. Great bokeh, perfect build quality, smaller than the Sigma, but larger than the Pentax. The one drawback (that doesn't bother me: manual focus (but it *does* have auto-aperture).

As for your two choices - I'd go with the Pentax for the slightly better bokeh and size.

[MadMathMind]

Thanks for all the great input, everyone! I'm not ready to make a decision yet, but this is definitely giving me the right things to think about!

My wife told me to get "the better one if [I] really want it." I was kinda hoping she would say "$1200 for a lens?!? are you kidding?!" but she wholly endorses whichever one I think is better. If there was any doubt she's a keeper up to this point, there now isn't. Still, it would make it simpler if she made the decision for me.

Can you go to a store and maybe touch, hold both lenses?

This is a great idea, but unfortunately, it's incredibly hard to find Pentax...anywhere in the USA that is not New York. I do get to travel a bit for business, so I can look for stores in the places I visit! Plus, if I make a trip back to Japan, there's always Yodobashi camera, although the hit from exchange rate and foreign transaction fees are pretty painful (but not worse than sales tax, I guess).

I can see that you want a quality outcome. If that is what you want, then Sigma it is, since you did not mention anything about weight.

No, I don't plan to use these lenses as walk arounds, so the weight isn't a big concern. But in light of what has been said here, it's probably a good idea to do what Na Horuk says.

If you are willing to lug around a monster of a lens, the upcoming Sigma 18-35 may be just the thing. Appears to nearly rival the 35 at 35, and just gets even better at the shorter end. Every review I've seen for it says it will be a peach. We should get it in K mount before the end of Q1 2014.

I thought about this. On the plus, it's also a 72mm filter ring, so that works nicely. It's also slightly less expensive than the 35 although the issue is...it's monstrous. I don't think I want to haul it around.

The rumour is that the FA's will be refreshed soon, presumably with HD rather than SMC, hopefully with better CA control and quick shift, and possibly with DC and WR. The last two seem unlikely. Anyway, I've decided to wait to see what these changes bring before making a decision on this question.

I was kinda hoping that if this happens, we can get the FAs on sale!

Not to feed the fire, but I recently had the same decision to make, and went an entirely different direction: Zeiss 35/2 ZK. It's around ~$700 on ebay new, as sharp (or almost) as the Sigma, very sharp wide open at f/2. Great bokeh, perfect build quality, smaller than the Sigma, but larger than the Pentax. The one drawback (that doesn't bother me: manual focus (but it *does* have auto-aperture).

I'm not willing to expand to manual focus. If I were, there's a lot of options in legacy Pentax glass. I have a few manual focus lenses only and it can be a real pain to focus them, especially if you want candid shots. It doesn't really work well to focus on a spot during a family gathering, as there's just not enough people moving through a particular spot.

[Adam]

I've used both of these lenses and it is really hard to say which is better.

I will try to explain why.

Image quality:

Even though, sharpness is very good on both lenses, bokeh is better on Sigma.
Color rendition. Well, both lenses render colors really nice, but I prefer the colder look that Sigma produces that the warmer from 31.
CA - Sigma is miles away, 31 suffers from CA pretty badly.

I give a point to Sigma here.

Build quality:

31 is all metal, looks like a jewel. Even though usually suffers from wobbly front element which isn't acceptable for such an expensive lens. Also, there is a little movement in the focus ring when camera is in AF mode (no QS for the 31). Yes, these are small things, but for 1.3K $ lens, they are hardly acceptable (IMO).
Sigma is mostly plastic, but has a metal mount. No wobble or anything, feels very solid. Features internal focusing, quick-shift which makes the lens feel high quality and very well build.

Hard to say which is better. I'd say it is a draw.

Auto focus:

31 is screwdrive, Sigma - HSM. Both focuses very fast and both lenses didn't need any AF adjustments (on K5IIs).

Win for Sigma (for silent focus)

Joy of use:

Sigma is a very large lens compared to Pentax. Heavy too. Grip is necessary for comfortable use (IMO). So, it is a little tiring to use it for two or more hours. The biggest drawback for the Sigma is that you may not have it when you need it.
Pentax 31 is small and light. It will fit in any camera bag, there is really no problem having it always with you.

Win for Pentax. Quite subjective, but I enjoyed using the 31Ltd a bit more.

Conclusion:

So, even though the overall score is Sigma 3, Pentax - 2, I'd say there is no real winner here. Both lenses are very good and you should get the one that suits your priorities better

Hope it helps

P.S. information written above is 100% subjective, based on my semi-pro use and it is absolutely normal if it varies from yours

Isn't the Sigma's barrel made of metal? I seem to remember that it felt much better than the 17-70 that I happened to be testing at the time.

[Apapukas]

Isn't the Sigma's barrel made of metal? I seem to remember that it felt much better than the 17-70 that I happened to be testing at the time.

Yes, I was a little wrong here. It is made partly from metal.
I'll post a pic showing that later