Originally posted by lol101 So tell me why the MF didn't overtake the 35mm film format?
Medium format can be surprisingly small, I have a 6x10 camera that is approximately 2x smaller than my K10 + grip.
While medium format can be surprisingly small, it usually isn't. Especially for dSLR systems. Plus consider that the 35mm format allowed for more shots on a single roll. Simply 35mm has a convenience advantage over medium format, which APS-C does not have over "Full Frame".
Originally posted by lol101 You left out the most important side of it: price of a given lens for a given FoV.
One could argue for example that the DA*50-135 is 1/2 the bulk and cost than a 70-200f2.8 would be or compare a 50mmf1.4 to a 85f1.4...
And one could also point out that a decent 12-24mm costs a lot more than a decent 19-35mm did. Or wonder where is the equivalent to the fast 35mm and 50mm lenses we used on the 135 format. Yes the 50mm f/1.4 can be compared to an 85mm f/1.4... so where is our 35mm f/1.4 to replace the FOV the 50mm gave us!? Well I guess there's always the 31mm f/1.8 Limited... still want to talk about price?
My point being that with the APS-C format some lenses seem cheaper (longer ones), some not, and some seem more expensive (wider ones). I'm not seeing a huge advantage one way or the other.
Originally posted by lol101 Another thing is that the quality advantage we see in FF cameras might vanish as technology progresses.
It could go two ways: the APS-C could improve (we'll see about that in the next few month) or the FF quality could "decrease" (as in "cram" 22Mpix+ in a FF sensor and compare to a 10-12MP APS-C sensor: the pixel size is about the same so what you get is more resolution, everything else being the same, but how much more resolution can your optics resolve and how much more resolution do 99% of the photographers need?)
At one point, you'll reach a resolution limit (in close relation with the lens design) where the sole advantage with FF over APS-C will be to have the choice between a few more pixels or a slight increase in high ISO quality, both of which will be utterly unimportant for 99% of photographers because differences will be visible on 4x3m size prints when inspected with a magnifier, but you'll remain with the larger/more expensive FF lenses for a given field of view.
What will drive the market won't be size or weight, heck it won't even be IQ when differences will be so minute you'll need to go 100% pixel peeping to see them, it will be price and I don't see how FF is ever going to be cheaper than APS-C.
FF will not become cheaper than APS-C. But it will get cheaper than it is now; significantly cheaper in time (as will APS-C); and if it retains a noticeable advantage in "IQ" then a fair number of people will still consider it worthwhile spending the extra.
As for IQ, of course APS-C will improve, but what makes you so certain that APS-C quality can only get better while FF quality can only get worse? The issue of pixel "cramming" applies to both. As the technology of APS-C sensors improve, so will that of 35x24mm sensors.
I continue to use the APS-C format because it does most of what I want (but not 99%), and because I can't afford any current FF cameras. When FF cameras become available for the price of current APS-C cameras, then I will most likely buy a FF camera, not buy an APS-C one simply because it's even cheaper.
Of course, if Pentax can make an APS-C camera that is 99% as good as the then-current FF cameras,
including being 99% as good at high ISO performance, then I will certainly consider it... but currently the advantage FF cameras have in that area is more than 1%, and I expect that to continue. We will of course have to wait and see, but I have no reason to believe that APS-C technology will continue to improve yet FF technology will not.