Originally posted by dakotapix If I've followed this discussion correctly, the OP asserted that the APS-C format had caught up with FF in the ultra-wide realm due to the availability of K-mount APS-C lenses with equal or greater FOV than those available for FF.
I suspect the OP asserted a bit more than that. For a long time we've been hearing about the advantages of FF in terms of wide angle photography. Wide-angle lenses for FF tend to be cheaper (especially legacy WA's) and they will of course perform better (at least in terms of center sharpness). For example, you can purchase an old M 28 f3.5 for around $60. The closest you can come to that FOV on APS-C is the DA 21, which is considerably more expensive (used prices approach $300). Is the DA 21 a better lens? Yes. But on FF the M 28 will outresolve the DA 21 on APS-C.
Yet despite this seeming huge advantage for FF, right now (and at least for the immediate future) K-1 landscape photographers are really struggling to find viable wide angle solutions, especially once they wish to go wider than 28mm. If you wish for state of the art optics, there are only two options available, and both are heavy and expensive f2.8 zooms. And if you want filter rings on a lens wider than 24mm, there's really no credible options currently available. Hence the rather ironic situation for the K-Mount, where APS-C actually enjoys, at least in terms of options involving high-end modern optics, an advantage over FF.
Originally posted by dakotapix One factor that I didn't see addressed directly (apologies if someone did) is the fact that for the same FOV, a FF lens is going to be working at a greater magnification, therefore may be able to perform better in the realm of sharpness, perhaps even with a less high quality lens.
Yes, that's true
for the center of the image. But that's not necessarily true for the edges. I've been looking at some FF images taken with the FA 20-35, and while the center of the image is definitely sharper than what I could get with the DA-12-24 on APS-C, the edges are not as sharp. Outside the APS-C crop, the resolution of the FA 20-35 seems to fall off a cliff. If you're a landscape photographer, the primary reason you would migrate to FF would be for the added resolution. But if you can't improve resolution across the entire frame, what's the point?
Originally posted by Adam What Pentax needs in the short term, IMO, is an affordable 20mm, 24mm, and/or 28mm prime lineup such as those in Nikon's F1.8 series. These can deliver solid performance without breaking the bank.
I would argue there's a greater need for a WA zoom with filter rings. An HD DFA 18-35 f4-5.6 with similar optical performance to the DFA 28-105 and filter rings could be sold at half the price (and perhaps half the weight) of the expensive and heavy DFA 15-30. Most landscape photographers need filter rings more than they need f2.8!