Originally posted by Nicolas06 In case of 18-35, it is insanely sharp and as also a very fast aperture while remaining sharp. It still has a flare problem through and from the samples I have seen you doesn't have the color rendition you have typically with high end pentax glass (DA*, even zooms, DA/FA ltd).
Sigma choosed the 18-35 f/1.8 route instead of the 17-50 f/1.8, not only for price; a 18-50 f/1.8 would have trouble to be of same quality as of a 18-35 f/1.8. 3X is a little too much while a such short focal at the begining of the range doesn't help. 24-70 f/1.8 might be easier to design (and something similar already exist in FF with at least f/2 I think).
Zoom vs Prime is not absolute. There focals that zooms handle better than others. A 50-135 or 70-200 tend to give very satisfory results. Transtandard tend to be not that good, in particular wide open, begining of the range. If the sigma change the game it is because of it's 2X range.
I completely agree on all points (although I'll just take your word for it on the sharpness - haven't examined that aspect yet, but if it's anything like my Sigma 8-16 it's sharp!).
No one's truly created a great 16/17/18-50/2.8 yet - how could we possibly expect a great f/1.8 lens with that range?!!
Originally posted by starjedi At the prime side, Pentax for sure can deliver some fast APS-C lens such as 24mm F1.2/35mm F1.2/50mm F1.2/85 F1.2 (their size will still be smaller than FF lenses as 85 F1.2 APS-C only lens will surely be smaller than a FF 85 F1.2). The price will also be lower and at the $1000-$1500 level instead of $2000+ level.
However, it is just a dream as Pentax apparently sticks with the portability on APS-C region and does not have strong motivation to challenge itself due to small market share. And as far as we know, lot of pentax prime lens are in fact ff compatible lens, which simply means that they are lazy to design as a lot of lights are wasted!
As for these primes, however, it may be technically feasible. In a photography culture where people fawn over the recent Fuji X systems, Sony A7 and A7r, and the Sigma 18-35/1.8, it actually
pays to make such attention-grabbing products. So if it could easily be done, I would expect someone might be doing it!
But it's not going to be Canon or Nikon, and probably not Sony. A $200 35mm f/1.8 APS-C only lens doesn't necessarily undermine FF when a FF f/1.4 version is available. But an APS-C f/1.2 lens could - especially when in theory it would cost less. And even Pentax doesn't want to go down that road now, with a FF likely coming out. So that leaves only third parties, and Sigma probably doesn't want to undermine sales of it's new 35/1.4 FF Art lens, for example. So who would do it?