Originally posted by Kunzite I don't "make you funny" - whatever that means; but your attacks are laughable.
Please read my posts carefully and don't ignore relevant parts; as I just said:
"According to Photozone, the Sigma Art 20mm and 24mm are quite weak in the corners, unless stopped down. That is understandable, as making fast ultra wide-angle SLR lenses is not easy. However, it should also help us realize that Sigma Art lenses are neither perfect, nor magical - they're simply high-end lenses, which is precisely what Pentax is targeting with the new D FA* line."
I also said that I hope the Pentax ultra-wide is not a huge, heavy f/1.4 - so why are you asking me if I'm shooting landscapes at 20mm or 24mm at f/1.4-2? OTOH you were saying there will be no DFA20/1.4 and DFA24/1.4 - then ignoring the Sigmas' performance at those apertures.
I proved quite well that at least some Sigma Art lenses are not "close to perfect". While there are reasons for that, perfect means perfect and such weak corners, heavy vignetting etc. aren't "close to perfect".
It would be interesting to see Pentax tackling these challenges. But, I have every intention of buying... while you, from what I see, are interested in putting Pentax down.
Photozone tested both these lenses on the 50 MP 5DsR, and they are known for being towards the harsher side when reviewing lenses from all manufacturers. Look at the commentary on Canon's 24-70mm f/2.8 II, considered to be one of, if not the best 24-70 f/2.8 available. They only gave it 3.5 stars for optical quality. It's also telling of the decline in Pentax popularity that none of the DFA lenses have been tested by any of the major photoreview sites. Unfortunately it makes quantifying their performance more difficult.
While their 20mm and 24mm lenses aren't as optically "perfect" as their 35mm, 50mm, and 85mm, they are definitely at the top of the class compared to similar primes. Like you said, it's not easy to make those lenses. Every other 24mm f/1.4 suffers from even worse vignetting. The corners are very tough to make. So I think it's very reasonable to say that Sigma's Art primes are some of the best available, considering optical performance and price. Of course they are heavy, but that's the price you pay with the modern fast primes.
So Pentax has a high standard to surpass if they're gunning to beat Sigma's Art primes. Especially since the 50mm, 85mm, and 35mm (next rumored pentax lenses) are considered to be the best in the Art series.
Originally posted by normhead
There's been lots of discussion, lots of folks who prefer one lens or the other. I'd suggest the biggest difference between the two lenses is weight. And the Sigma seems to have been able to make their lens cheaper by adding a lot of weight. That's great if you're looking at a framing hammer instead of a claw hammer but in photography weight serves no practical purpose, and folks , whatever the medium should expect to pay a premium for light weight practical gear over gear that's so heavy, you really don't want to use it. In canoeing I can buy a fibreglass pig for $1000 or an ultra-light easy to carry boat for $4000, so with other outdoor gear, people pay ridiculous prices for lightweight gear. I like my Sigma 70, but it rarely gets used as I have the FA 50 macro and Tamron 90 macro. It's great lens, but most of the time it's a shelf ornamaent.
So my moto remains, use sigma if you can't afford the Pentax and are young enough to handle the extra weight. On occasion I can afford the Pentax, and every year the weight becomes harder and harder to manage. So Sigma loses on both of the critical criteria.
Of my 3 Sigma lenses, I have nothing I want to keep, long term.
The Otus line is $4000 and has similar performance/weight characteristics to Sigma's art line, with a similar design philosophy. So it's not about paying for a cheaper lens in terms of weight. It's probably getting rid of that last bit of aberrations and getting to the f/1.4 aperture that you pay for with that huge increase in size and weight. The 31mm also shows more light falloff even despite being at f/1.8. I personally would like to have both lenses. One for the best performance, regardless of weight, and the other for an optimal mix of weight and performance.