Originally posted by Sandy Hancock No. No, no NO!
Can we please put this to bed? If you put an appropriately adapted medium format 80mm f/1.9 lens on the K-1 it will produce images somewhere between those of the FA 77/1.8 and the FA* 85/1.4 with respect to angle of view, with about the same and slightly more depth of field respectively wide open. A full frame 135mm lens will give a considerably tighter field of view.
The size of the image circle is irrelevant - what matters is how much of that circle is recorded by a given size sensor.
If I wasn't in an airpot lounge about to fly to Seattle I'd do some test shots to demonstrate it. I have a P645 to PK adaptor, and unless I'm seriously mistaken (and please correct me if I'm wrong), my adapted DFA645 35/3.5 should give the same field of view on the K-1 as my Sigma 35/1.4 Art. Likewise with my DFA645 55/2.8 and my DA* 55/1.4, and almost with my FA645 75/2.8 and FA 77/1.8
Anyway, back to the thread; I really wish I still had my Mamiya 80/1.9 - it was a gorgeous lens.
Yes, I love my Mamiya 80mm f 1.9, and actually I am pleased that it demonstrably yields an approximate 80/85mm FOV on the K-1, as per the three attached shots.
Any way, here is the same subject taken from the same distance with the Mamiya 645 80mm, an Auto Sears 135mm, and the Pentax-FA* 85mm f 1.4.
It seems as you said that the portion of the M80/1.9 image circle recorded on the K-1 sensor is almost exactly the same as the portion of the PK 85 FA*/1.4 image circle recorded on that same sensor, while the Sears 135mm lens is much tighter. This is a big surprise to me as I had been thinking that using the M80 on the K-1 was yielding a tighter image than it would yield on a 645 sensor.
Later I will give the M645-35 and some Pentax 35mm a try. I will also try the DFA645 55mm f 2.8 and one of my K-mount 55mm lenses.