[mills]

Well, I've read tonnes of reviews and threads, but am about to pull the trigger and find myself waffling. There's things I like about each of the two fast 30ish lenses and I cant make up my mind, so I'm rambling on the internet...

I want a fast 30mm. Indoors, low light... my 50's are too long, but when I do use them its generally f2-2.8, but I do dip below that now and then. I'm pushing my k10d as high in the ISO department as will look acceptable. I know that in theory I wouldnt miss much with the difference between f1.4 and 1.8, but somehow the 1.4 appeals to me. I could upgrade to a K5, but id still have a use for a fastish 30mm, and my k10 gets the job done most of the time. The upgrade is in the near future, but I'd rather go with the lense for now.


in terms of comfort, I prefer short and wide (30mm) to longer and thin (31mm), but the one 30mm ive found to try in person just didnt feel smooth/right when focusing manually and was really loud on auto. Havent used a 31mm but I assume its at least close in feel to my other pentax primes (15ltd, 30ltd, some k 50mms) which is amazing and quieter.

I probably wouldnt be using it for anything that needs razor sharp edge to edge, so those arguments are less important.

Cost difference isnt really a show stopper I just know that I like my sigma 10-20 and honestly would probably be fairly happy with either lens... At various points I've "decided" that each lens was the right answer and that I wouldnt think about it anymore, but that never lasts.

I dunno, not really much of a definate question, but is the 31mm close in feel to the da ltds? are both lenses about equally useable wide open? Is there any other advantage/disadvantage that I've left out and should think about? Do people actually shoot much in low light at 1.4 or does the small dof couteract any gains in shutter speed?

Thanks if anyone bothered to read my rambling. Theres a good chance I'll just go with a 31mm and get it over with though.

[Nuff]

The reasons why I chose 31mm over 30mm is because of weight and sharpness. 31mm is much sharper at edges, not to mention the smooth bokeh and the way it renders images.
It is by far my favourite all round lens.

[TOUGEFC]

I choose the Sigma 30mm because of sharpness and the way it isolates subjects.
The 30mm is much sharper in the center (where it counts the most)and its very sharp right from the get go at f/1.4 and it renders with a very distinct "3D" look, more than what the 31 can. Plus its faster.

Before I bought mine, I spent alot of time looking images from both lenses....and ended up choosing the Sigma.

[DogLover]

I choose the Sigma 30mm because of sharpness and the way it isolates subjects.
The 30mm is much sharper in the center (where it counts the most) and it renders with a very distinct "3D" look, more than what the 31 can. Plus its faster.

I've had both and Simon makes excellent points. The 31 is a wonderful lens, but honestly, if I had it to do over again and for the difference in cost, I would have kept my 30 and passed on the 31. Heresy, I know.

[civiletti]

As stated previously, the DA31 is sharp across the field, while the Sigma 30mm is soft at the edges. If you shoot wide open with a centered subject, the Sigma will work fine. If you want everything sharp, as in landscape photography, the DA31 is superior.

[yusuf]

I would chose Sigma 30mm for creative possibilities that f1.4 offers. To share my experience, I was planning to buy FA31 because of slightly wider focal length and especially due to very very high reputation it enjoys. Last week I got an opportunity to perform comparison between my FA35 and FA31. It turned out that FA35 is as good as FA31 including color rendition and bokeh, the only obvious difference is focal length. I still have to resize those pics and if someone interested, I can post it here. So for now, I've changed my mind and will be looking for Sigma 30mm instead of FA31mm

[Nuff]

Like civiletti has mentioned, the 30mm at f4 (the sharpest f-stop for both lenses) is sharper by ~100LW/PH in the centre, at other f-stops it's around 50LW/PH. That's according to photozone.
On the other hand on the border the 31mm at f4 is sharper by ~420LW/PH. Since 31mm isn't a portrait lens, but my general walk around lens, I want the whole frame to be sharp, from edge to edge. After all, it's a 48mm equivalent FF lens. It stays on my k5 about 60% of the time, so I also appreciate that it's also lighter. The weight of primes and other gear adds up in camera bag.

By the way, my portrait lens, 77mm is also sharper across the frame than Sigma 30mm. I guess the important this is, what do you want to use it for?
By the way, the 30mm CAs a lot worse than 31mm, that was another big reason why I didn't choose it. A lot of my photos are in snow or bright sun and correcting CA in PS becomes a pain after a while.

[twitch]

Another point of difference is that the FA31 is FF compatible and has an aperture ring, something of value if you want to shoot film or if a FF DSLR ever gets released.

[RickyFromVegas]

If you've got the dough, and you want the corner to corner sharpness, Go for 31mmLTD.
But Sigma 30mm is not to be underestimated either.

I chose Sigma30. It costs half as much as 31LTD, and I mainly use it for portrait, so corner resolution didn't interest me much.
I still haven't used it much, but color rendering, blur characteristics, sharpness open wide is much better than I initially thought when comparing against 31LTD.

[Eagle_Friends]

I would choose a FA 31mm every single time, given I can afford one... =[

[Tonto]

I was 90% ready to buy a Sigma before my Overseas trip earlier in the year but wasn't anywhere in stock and I was running out of time - FA31s at B&H dipped below US 1000 dollar mark when the Australian dollar was high and delivery from the US was quicker than any orders for the Sigma locally.
Anyway to the point, I WAS going to be using the 30/31 as a low light portrait lens for shooting across the dinner table when we were catching up with friends over a few drinks. For this both would be excellent and the FA31 was. What I found though was I used it for more wide shots than typical isolation type photos. Although it wasn't a true wide angle it was "Wide Enough" so when I was walking around it was a great compromise length for when I just wanted to carry around something small. For this reason the smaller size and the overall sharpness was perfect. I often carry two lenses this one and the 55-300 for everything else. Also my wife usually shoots strait to JPEG so having the lens correct in camera is nice too (I turn it off on my K7 though).
If I had my time again I MAY have still got the Sigma 30mm and paired it up with a FA43/DA40 as sometimes I feel 40mm is a more natural view for me on APSC.
One more thing though, the FA31 kicks ass on film!

[paperbag846]

Another point of difference is that the FA31 is FF compatible and has an aperture ring, something of value if you want to shoot film or if a FF DSLR ever gets released.

I would suggest that this is the major value. I have never tried the 31, but the 77 did not blow me away on digital as much as it did on film. The best lens I ever tried... but I feel like the k20d crippled it in a sense. The 31 is likely to be just as special, but I would only invest in it if it was going to see serious film time.

[elho_cid]

The answer is here:
http://s215846244.online.de/wsb4627126001/Testberichte/Normalbrennweitentest.pdf

In german, but very detailed comparison.

[Macario]

other things that the Ltd is better at than the Sigma
Less CAS, better vignetting charasteristics, and less distortion

[Rondec]

I personally chose the Sigma 30, mainly due to cost. The biggest areas which the FA limited are stronger: better out of focus areas and sharper edges, just aren't that important to me. Truthfully, having an f1.4 lens that is usable at f1.4 comes in handy, particularly when shooting in doors.