Originally posted by photoptimist
Indeed! To get a decently sharp lens, 180/2.2 on 6x7 would probably end up requiring a 95 mm or 112 mm filter and weighing a solid 2,000-3,000 grams.
The 200/4 for 6x7 takes a 77mm filter and weighs 756 g. Scaling that design up to f/2.2 adds at least 31 mm to the filter size, makes all the glass elements 6X heavier, and probably requires a more complex optical design to make it decent.
Or look at the Canon 200/2. It's 2500 g and costs $5,700 but only covers a small image circle of 35mm cameras. Adapting that design to double image circle would make the lens even bigger and heavier.
Fast apertures in 6x7 make for massive, expensive lenses.
Yes, but why go for 6x7 if you can get the same light gathering ability with a 36x24mm frame and a high end lens? Thats why i proposed several lenses at 180mm (FF equivalent 85mm portrait lens). The 180/4 limited for lightweight, affordability and high resolution. The 180/4 macro because we need a macro lens in the line up and 180 is a propriate allround focal length for that and f/4 to keep the weight and size down. The 180/2,2 would be an extreme high end lens for those that already have a 100 foot yacht and want a lens with truly out of the ordinary light gathering ability. Its 85mm f/1,0 equivalent.
@tuco: I believe the 180mm lenses would do the job for the 165mm ones. Pentax cant have 100 lenses for that system. I had to cut down on something. I believe the list of 14 lenses are more then long enough, I just couldnt figure out where to cut more. The launch plan are also quite optimistic. I gave them something to streatch for.

180mm (85mm eqv) are on the wide end of portrait lenses. A 165mm (77mm eqv) are on the very vide end. Some prefer 135mm eqv for portraits and thats what the D-6x7 300/3,5 are for. (140mm f/1,6 eqv)
Maybe I should add a portrait zoom for the lineup? A lens for head, half and full body, with shallow enough depth of field. Some prefer a 70-200 f/2,8 for portraits and allround use on 36x24mm frame. A 150-400mm f/5,6 would do the same job on a D-6x7. Maybe even push it til f/5,0.